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Ultracompact H II regions. II. New high-resolution radio images
Abstract
Radio continuum observations were made of 59 IRAS sources that have 100 μm flux densities ≥ 1000 Jy and far-infrared colors identified with ultracompact (UC) H II regions. Eighty percent were found to have associated compact radio sources. Seventy-five sources were detected at ≲1″ resolution at 3.6 and 2 cm wavelengths, for which we provide contour plots and flux density distributions ranging from the radio to the near-infrared. Over half are unresolved and their morphologies undetermined. The remaining sources can be described by only five morphological classes, whose frequency of occurrence is consistent with that of the Wood and Churchwell survey. We calculate physical properties of the nebulae and show that they are consistent with UC photoionized regions. Alternative explanations are explored and found to be unlikely. The correlation of UC H II region positions with proposed spiral arms is examined and found to be well correlated only for the local spiral arm or "spur." No obvious enhancement of UC H II regions is apparent along the proposed Sagittarius and Scutum arms, probably because of inaccuracies in the kinematic distances. We find the latitude distribution of UC H II regions to lie in the range 0°.5 ≤ |bFWHM| ≤ 0°.8. No correlation between size and density of cometary and core-halo UC H II regions is found, consistent with the bow shock interpretation of these morphologies. Spherical and unresolved UC H II regions, however, appear to show a trend toward lower densities with increasing size, as expected for expanding H II regions. The observed ratios of far-infrared to radio flux densities of UC H II regions lie in the range 103 to ≳ 105. By applying the results of model atmospheres, it is shown that this ratio depends on spectral type, ranging from ∼ 103 for an O4 star to ≳ 105 for a B3 star. We find that many of the UC H II regions in our sample must be excited by a cluster of stars, and most probably contain significant amounts of dust.
... QUIROGA-GONZÁLEZ ET AL. ∼ > 10 2 -10 3 5-10 3 5 Extended Emission a Adapted from Kurtz & Franco (2002); de la Fuente et al. (2020b). b 1.-Sewi lo et al. (2008,2004), 2. -Wood & Churchwell (1989), 3.- Kurtz et al. (1994), 4.- Lumsden et al. (2013), 5.-(de la Fuente et al. 2020a, and references therein). ...
... pure hydrogen and a canonical value for the electronic temperature of 10 4 K. The electronic density (n e ), emission measure (EM ), the mass of the ionized gas (M HII ), and the total rate of Lyman continuum photons of the ionizing star (N ′ c ) were calculated in the standard way using equations 1 to 4 (Schraml & Mezger 1969;Kurtz et al. 1994): -5, -3, 3, 5, 7, 9, 12, 15, 18;IRAS 07427-2400: -5, 5, 10, 20, 40, 60, 80;IRAS 07528-3441: -5, -3, 3, 5, 7, 9, 12, 15, 20, 25, 30, 35, 40, 45;IRAS 08189-3602: -4, -3, 3, 4, 5, 7, 9, 11, 13;IRAS 18094-1823: -5, -3, 3, 5, 7, 10, 15, 20, 30, 45;IRAS 19120+1103: -5, -3, 3, 5, 7, 10, 15, 20, 30, 40, 60, 80, 100, 150, 200, 250;IRAS 21306+5540: -5, -3, 3, 5, 7, 9, 12, 15, 18, 21;IRAS 21334+5039: -5, -3, 3, 5, 7, 9, 12, 15, 20, 25, 35, 45, 55, 65, 75, 85;IRAS 21413+5442: -5, -3, 3, 5, 7, 9, 12, 15, 20, 30, 40, 60, 80, 100, 120, 140, 160, 180;IRAS 22134+5834: -5, -3, 3, 5, 7, 9, 12, 15, 18;IRAS 22308+5812: -5, -3, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, and IRAS 23030+5958: -5, -3, 3, 5, 7, 9, 12, 15, 18 times the respective rms listed in Table 5. The beam size is shown at bottom left and given in Table 5. ...
... The physical parameters calculated from the 3.6 cm flux density are listed in Table 6. Most of the calculated parameters for the continuum sources meet the definition of the UC H II region according to Wood & Churchwell (1989); Kurtz et al. (1994). Although the determination of the physical parameters using the flux density at 3.6 cm is an acceptable approximation, a better characterization requires observations in at least two wavelengths to estimate their spectral index. ...
We present results from a sample of 106 high-luminosity IRAS sources observed with the Very Large Array in the B and C configurations. 96 sources were observed in the X-band and 52 in the K-band, with 42 of them observed at both wavelengths. We also used previously published observations in the C-band for 14 of them. The detection rate of sources with 3.6 cm continuum emission was ≈ 25%, while only 10% have emission at 1.3 cm. In order to investigate the nature of these sources, their physical parameters were calculated mainly using the 3.6 cm continuum emission, and for sources detected at two wavelengths, we used the best fit of three H iiregion models with different geometries. As a final result, we present a catalog of the detected sources, which includes their basic physical parameters for further analysis. The catalog contains 17 ultracompact H II regions and 3 compact H II regions.
... Indeed, Odenwald & Schwartz (1993) showed that there are three arms in projection in the Cygnus X region; the Local Arm with sources at <5 kpc, the Perseus Arm from 7-9.5 kpc, and the Outer Arm, from 10-12 kpc. Nonetheless, there does seem to be confusion in the literature with several papers after these results claiming that DR7 is as close as 1.5 kpc (Kurtz et al. 1994), which would place it at a distance consistent with that derived for the Cyg OB 2 cluster (1.7 kpc; Knödlseder 2000). Though they measure the H110α recombination line at −41 km s −1 , Du et al. (2011) assigned DR7 to the tangent position at 1.56 kpc. ...
... LyC 0.18 0.14 photons s −1 to account for its radio flux. Kurtz et al. (1994) were the first to make subarcsecond radio continuum images of DR7 with the VLA, taking data that had an image resolution of 0 5 at 2 cm and 0 9 at 3.6 cm. Kurtz et al. (1994) identified two compact sources in the region. ...
... Kurtz et al. (1994) were the first to make subarcsecond radio continuum images of DR7 with the VLA, taking data that had an image resolution of 0 5 at 2 cm and 0 9 at 3.6 cm. Kurtz et al. (1994) identified two compact sources in the region. The first, named G79.321+1.291, is considered to be an irregular compact H II region with an integrated 3.6 cm flux density of 6.4 mJy. ...
We present our fifth set of results from our mid-infrared imaging survey of Milky Way Giant H ii (GH ii ) regions with our detailed analysis of DR7 and K3-50. We obtained 20/25 and 37 μ m imaging maps of both regions using the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy. We investigate the multiscale properties of DR7 and K3-50 using our data in conjunction with previous multiwavelength observations. Near- to far-infrared spectral energy distributions of individual compact infrared sources were constructed and fitted with massive young stellar object (MYSO) models. We find eight out of the ten (80%) compact sources in K3-50 and three out of the four (75%) sources in DR7 are likely to be MYSOs. We derived luminosity-to-mass ratios of the extended radio subregions of DR7 and K3-50 to estimate their relative ages. The large spread in evolutionary state for the subregions in K3-50 likely indicates that the star-forming complex has undergone multiple star-forming events separated more widely in time, whereas the smaller spread in DR7 likely indicates the star formation subregions are more co-eval. DR7 and K3-50 have Lyman continuum photon rates just above the formal threshold criterion for being categorized as a GH ii region (10 ⁵⁰ photons s ⁻¹ ) but with large enough errors that this classification is uncertain. By measuring other observational characteristics in the infrared, we find that K3-50 has properties more akin to previous bona fide GH ii regions we have studied, whereas DR7 has values more like those of the non-GH ii regions we have previously studied.
... Indeed, Odenwald & Schwartz (1993) show that there are three arms in projection in the Cygnus X region; the Local Arm with sources at <5 kpc, the Perseus Arm from 7 − 9.5 kpc, and the Outer Arm, from 10 − 12 kpc. Nonetheless, there does seem to be confusion in the literature with several papers after these results claiming that DR7 is as close as 1.5 kpc (Kurtz et al. 1994), which would place it at a distance consistent with that derived for the Cyg OB 2 cluster (1.7 kpc; Knödlseder 2000). Though they measure the H110α recombination line at −41 km/s, Du et al. (2011) assign DR7 to the tangent position at 1.56 kpc. ...
... +0.14 −0.18 photons/s to account for its radio flux. Kurtz et al. (1994) were the first to make subarcsecond radio continuum images of DR7 with the VLA, taking data which had an image resolution of 0. 5 at 2 cm and 0. 9 at 3.6 cm. Kurtz et al. (1994) identified two compact sources in the region. ...
... Kurtz et al. (1994) were the first to make subarcsecond radio continuum images of DR7 with the VLA, taking data which had an image resolution of 0. 5 at 2 cm and 0. 9 at 3.6 cm. Kurtz et al. (1994) identified two compact sources in the region. The first, named G79.321+1.291, is considered to be an irregular compact H II region with an integrated 3.6 cm flux density of 6.4 mJy. ...
We present our fifth set of results from our mid-infrared imaging survey of Milky Way Giant HII (GHII) regions with our detailed analysis of DR7 and K3-50. We obtained 20/25 and 37um imaging maps of both regions using the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). We investigate the multi-scale properties of DR7 and K3-50 using our data in conjunction with previous multi-wavelength observations. Near to far-infrared spectral energy distributions of individual compact infrared sources were constructed and fitted with massive young stellar object (MYSO) models. We find eight out of the ten (80%) compact sources in K3-50 and three out of the four (75%) sources in DR7 are likely to be MYSOs. We derived luminosity-to-mass ratios of the extended radio sub-regions of DR7 and K3-50 to estimate their relative ages. The large spread in evolutionary state for the sub-regions in K3-50 likely indicates that the star-forming complex has undergone multiple star-forming events separated more widely in time, whereas the smaller spread in DR7 likely indicates the star formation sub-regions are more co-eval. DR7 and K3-50 have Lyman continuum photon rates just above the formal threshold criterion for being categorized as a GHII region (10^50 photons/s) but with large enough errors that this classification is uncertain. By measuring other observational characteristics in the infrared, we find that K3-50 has properties more akin to previous bona fide GHII regions we have studied, whereas DR7 has values more like those of the non-GHII regions we have previously studied.
... Wink et al. (1982) carried out a pioneer single-dish radio continuum survey toward 85 UC H II regions. Wood & Churchwell (1989) and Kurtz et al. (1994) selected dozens of UC H II regions from the IRAS survey and performed high-resolution VLA observations toward these regions. Walsh et al. (1998) carried out a survey toward hundreds of UC H II regions with the ATCA. ...
... This approximation has larger uncertainties for MDCs at relatively late evolution stages, e.g., when a bright UC H II region has formed. Lyman continuum flux as a function of bolometric luminosity is shown in Figure 7, where we also plot the data of the UC H II regions obtained from Kurtz et al. (1994) and the expected Lyman continuum flux of a single ZAMS star (Thompson 1984). The ZAMS line is a theoretical upper limit of the Lyman continuum flux produced by photoionization. ...
... Following Cao19, we classify the sample into three categories as starless, IR quiet, and IR bright, a supposed Kurtz et al. (1994); the dots in other colors represent radio jets obtained from the literature. The green star marks the highest possible radio luminosity of a jet originating from a low-mass YSO (Shang et al. 2004). ...
We have carried out a high-sensitivity and high-resolution radio continuum study toward a sample of 47 massive dense cores (MDCs) in the Cygnus X star-forming complex using the Karl G. Jansky Very Large Array, aiming to detect and characterize the radio emission associated with star-forming activities down to ∼0.01 pc scales. We have detected 64 radio sources within or closely around the FWHMs of the MDCs, of which 37 are reported for the first time. The majority of the detected radio sources are associated with dust condensations embedded within the MDCs, and they are mostly weak and compact. We are able to build spectral energy distributions for eight sources. Two of them indicate nonthermal emission and the other six indicate thermal free–free emission. We have determined that most of the radio sources are ionized jets or winds originating from massive young stellar objects, whereas only a few sources are likely to be ultracompact H ii regions. Further quantitative analyses indicate that the radio luminosity of the detected radio sources increases along the evolution path of the MDCs.
... Observational studies targeting massive star formation are more challenging compared with their low-mass counterparts due to massive stars forming on short timescales and in clustered environments (Kratter & Matzner 2006). Because the massive star-forming regions are on average more distant compared with the areas forming low-mass stars, there are additional limitations of angular resolution and sensitivity of observing facilities (Kurtz et al. 1994;Churchwell 2002). Despite these difficulties, studies of the massive star formation are crucial, as they continuously influence the evolution of galaxies by emitting protostellar jets, ejecting stellar materials, accreting gas, and various other mechanisms. ...
... ± 0.4 km s −1 . Kurtz et al. (1994) estimated the lower limit of the Lyman-continuum photon rate in the region, based on which they assigned a spectral type of B0.5 to the central ionizing star. ...
... Our estimate of the Lyman-continuum photon rate is in good agreement with that of Zhang et al. (2017), who found log N Ly = 48.68 using the radio continuum data from the 1.4 GHz NRAO VLA Sky Survey (NVSS; Condon et al. 1998), but is significantly higher than that of Kurtz et al. (1994), who found log N Ly = 46.82 using observations of the region at 8.4 GHz with the VLA in the B-configuration. ...
We report the results obtained from a multiwavelength study of the H ii region G18.148−0.283 using the upgraded Giant Metrewave Radio Telescope at 1350 MHz, along with other archival data. In addition to the radio continuum emission, we have detected the H169 α and H170 α radio recombination lines toward G18.148−0.283 using a correlator bandwidth of 100 MHz. The moment-1 map of the ionized gas reveals a velocity gradient of approximately 10 km s ⁻¹ across the radio continuum peaks. The ¹² CO ( J = 3−2) molecular line data from the CO High-Resolution Survey (COHRS) also show the presence of two velocity components that are very close to the velocities detected in the ionized gas. The spectrum and position–velocity diagram from CO emission reveal molecular gas at an intermediate-velocity range bridging the velocity components. We see mid-infrared absorption and far-infrared emission establishing the presence of a filamentary infrared dark cloud, the extent of which includes the targeted H ii region. The magnetic field inferred from dust polarization is perpendicular to the filament within the H ii region. We have also identified two O9 stars and 30 young stellar objects toward the target using data from the Two Micron All Sky Survey (2MASS), UKIRT Infrared Deep Sky Survey (UKIDSS), and Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE). Cumulatively, this suggests that the region is the site of a cloud–cloud collision that has triggered massive star formation and subsequent formation of an H ii region.
... The main scientific driver of the project is to measure the Core Mass Function (CMF) in a statistically significant (> 500) sample of cores that spans the full range of gas masses, from sub-solar to ≳ 100 M ⊙ (e.g., Motte et al. 2018), something that can only be achieved by observing massive protocluster clumps at different evolutionary stages. The more evolved protocluster clumps in the sample have increasingly important feedback by ionisation from ultracompact (UC) and hypercompact (HC) Hii regions (e.g., Kurtz et al. 1994;Churchwell 2002;Hoare et al. 2007;Purcell et al. 2013;Klaassen et al. 2018). The corresponding free-free continuum emission can be an important "contaminant" for the otherwise dust-only ALMA millimeter continuum maps. ...
... However, there is no reason to think that all UC Hii regions will be ionized by stars of the same mass at the moment of observation, and to follow the same path on the n e vs D diagram as they expand and rarefy. A possible cause for our differing results with respect to previous surveys is that those have focused on the brightest UC Hii regions within rather evolved targets, selected from their mid-IR colors (e.g., Wood & Churchwell 1989;Kurtz et al. 1994). In contrast, the UC Hii regions in our sample are distributed in a broad range of protocluster evolutionary stages, and in different locations within a given protocluster. ...
We use the H recombination line to create templates of the millimeter free-free emission in the ALMA-IMF continuum maps, which allows to separate it from dust emission. This method complements spectral-index information and extrapolation from centimeter wavelength maps. We use the derived maps to estimate the properties of up to 34 HII regions across the ALMA-IMF protoclusters. The hydrogen ionizing-photon rate and spectral types follow the evolutionary trend proposed by Motte et al. The youngest protoclusters lack detectable ionized gas, followed by protoclusters with increasing numbers of OB stars. The total increases from s to s. We used the adjacent He line to measure the relative number abundances of helium, finding values consistent with the Galactic interstellar medium, although a few outliers are discussed. A search for sites of maser amplification of the H line returned negative results. We looked for possible correlations between the electron densities (), emission measures (EM), and with HII region size D. The latter are the better correlated, with . This favors interpretations where smaller ultracompact HII regions are not necessarily the less dynamically evolved versions of larger ones, but rather are ionized by less massive stars. Moderate correlations were found between dynamical width with D and . increases from about one to two times the ionized-gas sound speed. Finally, an outlier HII region south of W43-MM2 is discussed. We suggest that this source could harbor an embedded stellar or disk wind.
... The H II regions are seen in different morphologies, such as spherical, cometary, core-halo, shell, and irregular (Wood and Churchwell, 1989;Motte et al., 2018), which occur due to reasons such as the motion of the star through the natal molecular cloud, density gradient in the environment, the temperature gradient of the gas, etc. H II regions are classified based on their size and electron density, with regions with sizes ≤ 0.1 pc and densities ≥ 10 4 cm −3 being called ultracompact H II regions (UCHRs; Wood and Churchwell 1989;Kim and Koo 2001). Wood and Churchwell (1989) and Kurtz et al. (1994) noted that the Ly-photon rate inferred from the radio continuum emission of UCHRs was significantly lower (∼ 90%) than that inferred from far infrared fluxes measured by IRAS. This was suggested to be due to the absorption of Ly-photons by a large amount of dust in the H II region. ...
... meaning 78% of the intrinsic Ly-photons produced by the ionizing stars are not absorbed by the dust and contribute to maintaining the ionization of the H II region. Our estimation of f indicates that the fraction of Ly-photons absorbed by the dust is roughly 20% (compared to ∼ 90% before; Kurtz et al. 1994). Thus the detection of extended emission surrounding the UC core significantly reduces the requirement of a large amount of dust proposed in the earlier studies and provides an explanation for the Ly-photons that were missing in the combined studies using the radio and infrared wavelengths. ...
Studies of ultracompact H II regions have shown that the Lyman-continuum photon (hereafter, Ly-photon) rates inferred from the radio emission and values based on the infrared emission are inconsistent with a rate estimated from radio being up to 90% lower. One possible solution to this inconsistency is the presence of extended radio emission associated with the ultracompact core, which is undetected by most interferometric arrays, due to the lack of very short baselines. Since such extended emission would require a significantly higher rate of Ly-photons to keep its ionization state compared to the compact core, its existence would also resolve the “age problem of the ultracompact H II regions: the number of ultracompact H II regions observed in the Galaxy is much larger than what is expected based on their dynamical age (sound crossing time)”, as there is no need to confine the ionized gas within the ultracompact core. To test this hypothesis, we conducted a study of eight ultracompact H II regions with extended emission using radio data from the upgraded Giant Metrewave Radio Telescope (1.25–1.45 GHz) and the GLOSTAR survey (4–8 GHz), and infrared data from the UKIDSS, 2MASS, MIPSGAL, and Hi-GAL surveys. From our study, we found that the Ly-photon rate inferred from the radio emission is consistent with that inferred from the total infrared luminosity to within 20–30% when we include the extended emission. Furthermore, we identified the candidate ionizing stars and observed that, in some cases, multiple stars were responsible for ionizing the neutral gas in an ultracompact H II region. Here, we present the key results for one region (G19.68–0.13) out of the entire list of our targets.
... and G45.47 + 0.05 are about 10 3 -10 4 times more luminous than the shock-ionization model. A sample of ultracompact (UC) H II regions (Kurtz et al. 1994) have similarly elevated radio luminosities. ...
... The red dashed line shows radio emission from an optically thin H II region photoionized by zero-age main sequence stars (Thompson 1984), while the red solid line is the equivalent model for the fiducial TCA model protostar (initial core mass M c = 60 M e ; mass surface density of clump environment Σ cl = 1 g cm −2 ) (Tanaka et al. 2016). Yellow circles show a low-mass protostar (Anglada 1995) with a power-law fit of ( ) L 8 10 3 (Kurtz et al. 1994). up to ∼10 5 -10 7 K, with the maximum temperature reached increasing with increasing protostellar mass. ...
Massive protostars launch accretion-powered, magnetically collimated outflows, which play crucial roles in the dynamics and diagnostics of the star formation process. Here we calculate the shock heating and resulting free–free radio emission in numerical models of outflows of massive star formation within the framework of the Turbulent Core Accretion model. We postprocess 3D magnetohydrodynamic simulation snapshots of a protostellar disk wind interacting with an infalling core envelope, and calculate shock temperatures, ionization fractions, and radio free–free emission. We find heating up to ∼10 ⁷ K and near-complete ionization in shocks at the interface between the outflow cavity and infalling envelope. However, line-of-sight averaged ionization fractions peak around ∼10%, in agreement with values reported from observations of massive protostar G35.20-0.74N. By calculating radio-continuum fluxes and spectra, we compare our models with observed samples of massive protostars. We find our fiducial models produce radio luminosities similar to those seen from low- and intermediate-mass protostars that are thought to be powered by shock ionization. Comparing to more massive protostars, we find our model radio luminosities are ∼10–100 times less luminous. We discuss how this apparent discrepancy either reflects aspects of our modeling related to the treatment of cooling of the post-shock gas or a dominant contribution in the observed systems from photoionization. Finally, our models exhibit 10 yr radio flux variability of ∼5%, especially in the inner 1000 au region, comparable to observed levels in some hypercompact H ii regions.
... The distribution of the radio continuum emission is also shown in the figure. A UC H II region was previously detected in this region by Bally & Predmore (1983) and Kurtz et al. (1994). Even though the region has been studied from different perspectives and strong evidence of recent star formation activity has been found, no study has been conducted so far to probe the embedded filaments and their role in the star formation process associated with this H II region. ...
... The photogeometric distances of the point sources were obtained from Bailer-Jones et al. The UC H II region detected by Bally & Predmore (1983) and Kurtz et al. (1994) is also marked by a cyan hexagon. ...
We present a detailed study of the Sh2-87 H ii region using a multiwavelength data set in optical to radio bands. A Herschel column density map revealed that the host cloud is filamentary in nature, and together they formed a central dense hub. The extinction map generated using near-infrared photometric data also signifies the nonuniform distribution of the cloud and reveals its filamentary nature. We estimated a sizable variable extinction over the region up to A V = 34.4 mag, with an average value of A V = 3.4 mag. Using the various infrared color–color criteria, we identified 13 Class I and 202 Class II young stellar objects (YSOs) and 22 H α -emitting sources toward this region. Further analysis showed that the cluster is mainly composed of low-mass YSOs with a typical age of ∼3 Myr having masses in the range of 0.1–6.0 M ⊙ . The identified evolved YSOs (i.e., Class II YSOs) are primarily distributed along the filaments and in the outer parts of the cloud, while the recent star formation, inferred by the presence of Class I YSOs, ionized gas, and star-forming clumps, is observed in the hub region. The overall star formation scenario in the Sh2-87 region resembles the global hierarchical collapse model of star formation, where younger massive star formation activity is expected at the central hub along with the distribution of evolved low-mass YSOs in the filaments and the outer parts of the cloud.
... Hence, the disentanglement of dust and free-free contributions in the millimeter photometry of massive star-forming clouds is necessary to ensure a correct interpretation of observations. Therefore, in addition to studies of (dust-traced) cloud structure and fragmentation, it is important to quantify the presence of ionizing feedback from massive stars and their resulting H II regions (e.g., Kurtz et al. 1994;Purcell et al. 2013;Ginsburg et al. 2016). These feedback processes are also a key factor in the self-regulation of star formation, with implications for the overall structure and evolution of the interstellar medium (e.g., Peters et al. 2010;Dale et al. 2014). ...
... The amount of ionizing feedback is a potential way of tracing the evolution of massive star formation regions. This is usually done using as tracers the free-free continuum and hydrogen recombination line emission associated with compact and UC H II regions (e.g., Kurtz et al. 1994;Kalcheva et al. 2018;Rivera-Soto et al. 2020). For the ALMA-IMF sample, Motte et al. (2022) proposed an evolutionary sequence based on the far-IR emission and the surface density of H41α recombination line emission. ...
We present the combination of ALMA-IMF and single-dish continuum images from the MUSTANG-2 Galactic Plane Survey (MGPS90) at 3 mm and the Bolocam Galactic Plane Survey (BGPS) at 1 mm. Six and 10 out of the 15 ALMA-IMF fields are combined with MGPS90 and BGPS, respectively. The combination is made via the feathering technique. We used the dendrogram algorithm throughout the combined images, and performed further analysis in the six fields with the combination in both bands (G012.80, W43-MM1, W43-MM2, W43-MM3, W51-E, W51-IRS2). In these fields, we calculated spectral index maps and used them to separate regions dominated by dust or free–free emission, and then performed further structural analysis. We report the basic physical parameters of the dust-dominated (column densities, masses) and ionized (emission measures, hydrogen ionization photon rates) structures. We also searched for multiscale relations in the dust-dominated structures across the analyzed fields, finding that the fraction of mass in dendrogram leaves (which we label leaf mass efficiency (LME)) as a function of molecular gas column density follows a similar trend: a rapid, exponential-like growth, with maximum values approaching 100% in most cases. The observed behavior of the LME with the gas column is tentatively interpreted as an indicator of large star formation activity within the ALMA-IMF protoclusters. W51-E and G012.80 stand out as cases with comparatively large and reduced potential for further star formation, respectively.
... and G45.47+0.05 are about 10 3 to 10 4 times more luminous than the shockionization model. A sample of ultracompact (UC) HII regions (Kurtz et al. 1994) have similarly elevated radio luminosities. ...
... Large circles are eight protostars from the SOFIA Massive Star Formation Survey (De Buizer et al. 2017;Rosero et al. 2019) (see legend). Crosses are ultracompact HII regions (Kurtz et al. 1994). scale, they remain mostly optically thin, i.e., with flat radio spectral indices. ...
Massive protostars launch accretion-powered, magnetically-collimated outflows, which play crucial roles in the dynamics and diagnostics of the star formation process. Here we calculate the shock heating and resulting free-free radio emission in numerical models of outflows of massive star formation within the framework of the Turbulent Core Accretion model. We post-process 3D magneto-hydrodynamic simulation snapshots of a protostellar disk wind interacts with an infalling core envelope, and calculate shock temperatures, ionization fractions, and radio free-free emission. We find heating up to ~10^7 K and near complete ionization in shocks at the interface between the outflow cavity and infalling envelope. However, line-of-sight averaged ionization fractions peak around ~10%, in agreement with values reported from observations of massive protostar G35.20-0.74N. By calculating radio continuum fluxes and spectra, we compare our models with observed samples of massive protostars. We find our fiducial models produce radio luminosities similar to those seen from low and intermediate-mass protostars that are thought to be powered by shock ionization. Comparing to more massive protostars, we find our model radio luminosities are ~10 to 100 times less luminous. We discuss how this apparent discrepancy either reflects aspects of our modeling related to the treatment of cooling of the post-shock gas or a dominant contribution in the observed systems from photoionization. Finally, our models exhibit 10-year radio flux variability of ~5%, especially in the inner 1000 au region, comparable to observed levels in some hyper-compact HII regions.
... This source has been characterized as being a high luminosity (∼1.4-1.6 × 10 5 L e ) (Hernández-Hernández et al. 2014;Maud et al. 2015) shell-like hypercompact H II region and a hot molecular core (Walsh et al. 2003;Sewilo et al. 2004;Qin et al. 2008) at a near kinematic distance of d 5.7 kpc 0.8 0.5 = -+ (Fish et al. 2003), based on a systemic velocity of v sys = 95.6 ± 0.5 km s −1 (Qin et al. 2008), which is consistent with our observations of hot core line tracers in the source (see Section 3.3). We note that some previous studies adopted the far kinematic distance of 9.1 kpc (Kurtz et al. 1994;de la Fuente et al. 2020); however, as discussed later in Section 3.2, we are able to make a new astrometric confirmation of the near distance and so adopt d = 5.7 kpc throughout this work. ...
... c Sewiło et al. (2011), but the 1.3 cm flux has been rederived here. d Kurtz et al. (1994). e Walsh et al. (1998); uncertainties were not provided, so we adopt a fiducial value of 10%. ...
We report high-resolution 1.3 mm continuum and molecular line observations of the massive protostar G28.20-0.05 with Atacama Large Millimeter/submillimeter Array. The continuum image reveals a ring-like structure with 2000 au radius, similar to morphology seen in archival 1.3 cm Very Large Array observations. Based on its spectral index and associated H30 α emission, this structure mainly traces ionized gas. However, there is evidence for ∼30 M ⊙ of dusty gas near the main millimeter continuum peak on one side of the ring, as well as in adjacent regions within 3000 au. A virial analysis on scales of ∼2000 au from hot core line emission yields a dynamical mass of ∼80 M ⊙ . A strong velocity gradient in the H30 α emission is evidence for a rotating, ionized disk wind, which drives a larger-scale molecular outflow. An infrared spectral energy distribution (SED) analysis indicates a current protostellar mass of m * ∼ 40 M ⊙ forming from a core with initial mass M c ∼ 300 M ⊙ in a clump with mass surface density of Σ cl ∼ 0.8 g cm ⁻² . Thus the SED and other properties of the system can be understood in the context of core accretion models. A structure-finding analysis on the larger-scale continuum image indicates G28.20-0.05 is forming in a relatively isolated environment, with no other concentrated sources, i.e., protostellar cores, above ∼1 M ⊙ found from ∼0.1 to 0.4 pc around the source. This implies that a massive star can form in relative isolation, and the dearth of other protostellar companions within the ∼1 pc environs is a strong constraint on massive star formation theories that predict the presence of a surrounding protocluster.
... In the previous section, we presented the physical parameters for 26 compact Hii regions. In Table 6, we summarise the criteria for HC Hii, UC Hii regions, and the intermediate objects between these stages (e.g., Wood & Churchwell 1989;Kurtz et al. 1994;Gaume et al. 1995;Kurtz & Hofner 2005;Hoare et al. 2007;Yang et al. 2021). ...
In this study we present 18 to 24 GHz and high angular resolution radio wavelength Australia Telescope Compact Array follow up observations towards a sample of 39 HC HII region candidates. These objects, taken from a sample hosting 6.7 GHz methanol masers, were chosen due to the compact and optically thick nature of their continuum emission. We have detected 27 compact radio sources and constructed their spectral energy distributions over the 5 to 24 GHz range to determine the young HII regions physical properties, i.e., diameter, electron density ne, emission measure, Lyman continuum flux NLy and turnover frequency. The flux measurements are fitted for 20 objects assuming an ionisation bounded HII region with uniform density model. For the remaining 7 objects that lack constraints spanning both their optically thick and thin regimes, we utilise relations from the literature to determine their physical properties. Comparing these determined parameters with those of known hypercompact and ultracompact HII regions, we have identified 13 HC HII regions, 6 intermediate objects that fall between HC HII and UC HII regions, 6 UC HII regions and one radio jet candidate which increases the known population of HC HII regions by 50 per cent. All the young and compact HII regions are embedded in dusty and dense clumps and 80 percent of the HC HII regions identified in this work are associated with various maser species. Four of our radio sources remain optically thick at 24 GHz, we consider these to be amongst the youngest HC HII regions.
... These colour selected samples are not able to distinguish between MYSO and the more evolved Hii region stages, however, the latter stage is bright at radio wavelengths. Work by Wood & Churchwell (1989) and Kurtz et al. (1994) with the VLA was able to separate these two stages, resulting in the identification of ∼100 ultracompact (UC) Hii regions and allowing their physical properties to be characterised. Molinari et al. (1996) applied colour cuts to the IRAS PSC and identified 260 objects with properties consistent with being embedded high-mass protostars. ...
Over the past 20 years, the Galactic plane has been surveyed at high resolution at wavelengths from 1 micron through to 20 cm. The combination of these surveys has produced large samples of deeply embedded young stars located across the Galactic disc. These continuum surveys are complemented by spectral line surveys of thermal, radio recombination, and molecular maser (OH, H 2 O, CH 3 OH) lines. The identified sources cover the whole range of evolutionary stages in the star formation process, allowing the physical properties of these stages to be measured. This information has been used to calculate the star formation efficiency and star formation rate of the Milky Way and to evaluate the impact of environment and location within the disc. This review provides an overview of some of the most significant studies in recent years and discusses how the evolutionary sequence has been used to investigate the correlation of other star formation tracers and maser associations.
... We explored the excess VLA emission by measuring a brightness temperature for our C + X-band results at Component A to be 10 2.9 K. This is perhaps indicative of a region of star formation, such as in the H II regions studied in Kurtz et al. (1994) which showed brightness temperatures of 10 4 K (also see Figure 4 of Condon 1992). By contrast, the brightness temperature of 10 5.8 K for Component A from the VLBA measurements in FRAMEx III is consistent with a weak AGN (e.g., Ulvestad et al. 2005;Radcliffe et al. 2018) or perhaps strong star formation. ...
We present the first results from Karl G. Jansky Very Large Array (VLA) observations as a part of the Fundamental Reference Active Galactic Nucleus (AGN) Monitoring Experiment, a program to understand the relationship between AGN accretion physics and wavelength-dependent position as a function of time. With this VLA survey, we investigate the radio properties from a volume-complete sample of 25 hard X-ray-selected AGNs using the VLA in its wideband mode. We observed the targets in the A-array configuration at 4–12 GHz with all polarization products. In this work, we introduce our calibration and imaging methods for this survey, and we present our results and analysis for the radio-quiet AGN NGC 4388. We calibrated and imaged these data using the multiterm, multifrequency synthesis imaging algorithm to determine its spatial, spectral, and polarization structure across a continuous 4–12 GHz band. In the AGN, we measure a broken power law spectrum with α = − 0.06 below a break frequency of 7.3 GHz and α = − 0.34 above. We detect polarization at subarcsecond resolution across both the AGN and a secondary radio knot. We compare our results to ancillary data and find that the VLA radio continuum is likely due to AGN winds interacting with the local interstellar medium that gets resolved away at subparsec spatial scales as probed by the Very Long Baseline Array. A well-known ionization cone to the southwest of the AGN appears likely to be projected material onto the underside of the disk of the host galaxy.
... At millimeter wavelengths, we estimated a flat spectral index of −0.15 for this source, which is consistent with an optically thin emission from the UC H II region. The rate of ionizing photons needed to maintain such a UC H II region is ∼2.5 × 10 48 s −1 (Kurtz et al. 1994), which is compatible with a ZAMS star of spectral type O7.5-O8 (Panagia 1973;Martins et al. 2005). The position of this UC H II region is coincident with the dusty shell suggesting a probable relationship with the origin of the explosion as the sources Src I and BN in the Orion-KL region (Zapata et al. 2011). ...
In the last years there has been a substantial increase in the number of the reported massive and luminous star-forming regions with related explosive outflows thanks to the superb sensitivity and angular resolution provided by the new radio, infrared, and optical facilities. Here, we report one more explosive outflow related with the massive and bright star-forming region IRAS 12326−6245 using Band 6 sensitive and high-angular-resolution (∼0.″2) Atacama Large Millimeter/Submillimeter Array observations. We find over 10 molecular and collimated well-defined streamers, with Hubble–Lemaitre–like expansion motions, and pointing right to the center of a dusty and molecular shell (reported for the first time here) localized in the northern part of the UC H ii region known as G301.1A. The estimated kinematic age and energy for the explosion are ∼700 yr and 10 ⁴⁸ erg, respectively. Taking into account the recently reported explosive outflows together with IRAS 12326−6245, we estimate an event rate of once every 90 yr in our Galaxy, similar to the formation rate of massive stars.
... Thus, the feedback from M1 can in fact collapse the surrounding molecular cloud to create a new generation of stars. We have also found very young YSOs (class I, age < 0.5 Myr; Evans et al. 2009) and two UC H II regions (age < 0.1 Myr; Wood & Churchwell 1989;Kurtz et al. 1994;Meng et al. 2022) in the shell/ring around the massive star. The diffuse population of YSOs (age < 3 Myr) outside the E70 cluster might have formed independently, as it is not feasible to drift a few parsecs away from the cluster boundary in the short time span of their formation. ...
We present a comprehensive analysis of the Galactic mid-infrared bubble [HKS2019] E70 (E70) by adopting a multiwavelength approach to understand the physical environment and star formation scenario around it. We identified a small (radius ∼1.7 pc) stellar cluster inside the E70 bubble, and its distance is estimated as 3.26 ± 0.45 kpc. This cluster is embedded in the molecular cloud and hosts massive stars, as well as young stellar objects (YSOs), suggesting active star formation in the region. The spectral type of the brightest star (M1) of the E70 cluster is estimated as O9V, and a circular ring/shell of gas and dust is found around it. The diffuse radio emission inside this ring/shell, the excess pressure exerted by the massive star M1 at the YSO’s core, and the distribution of photodissociation regions, a class I YSO, and two ultracompact H ii regions on the rim of this ring/shell clearly suggest positive feedback of the massive star M1 in the region. We also found a low-density shell-like structure in the ¹² CO( J = 1–0) molecular emission along the perimeter of the E70 bubble. The velocity structure of the ¹² CO emission suggests that the feedback from the massive star appears to have expelled the molecular material, and the subsequent swept-up material is what appears as the E70 bubble.
... Thus, the feedback from M1 can in fact collapse the surrounding molecular cloud to create a new generation of stars. We have also found very young YSOs (Class i, age < 0.5 Mys, Evans et al. 2009) and two UC H ii region (age < 0.1 Myr, Wood & Churchwell 1989;Kurtz et al. 1994;Meng et al. 2022) in the shell/ring around the massive star. The diffuse population of the YSOs (age < 3 Myr) outside the E70 cluster might have formed independently as it is not feasible to drift out a few pc away from the cluster boundary in the short time span of their formation. ...
We present a comprehensive analysis of the Galactic mid-infrared (MIR) bubble [HKS2019] E70 (E70) by adopting a multi-wavelength approach to understand the physical environment and star formation scenario around it. We identified a small (radius ~1.7 pc) stellar clustering inside the E70 bubble and its distance is estimated as 3.26 +/- 0.45 kpc. This cluster is embedded in the molecular cloud and hosts massive stars as well as young stellar objects (YSOs), suggesting active star formation in the region. The spectral type of the brightest star 'M1' of the E70 cluster is estimated as O9V and a circular ring/shell of gas and dust is found around it. The diffuse radio emission inside this ring/shell, the excess pressure exerted by the massive star 'M1' at the YSOs core, and the distribution of photo-dissociation regions (PDRs), a Class I YSO, and two ultra-compact (UC) H II regions on the rim of this ring/shell, clearly suggest positive feedback of the massive star 'M1' in the region. We also found a low-density shell-like structure in 12 CO(J=1-0) molecular emission along the perimeter of the E70 bubble. The velocity structure of the 12 CO emission suggests that the feedback from the massive star appears to have expelled the molecular material and subsequent swept-up material is what appears as the E70 bubble.
... Using the NIR spectroscopic study, Vasyunina (2010) obtained a similar age of 1-3 Myr for T1. Previous results also suggested that T1 is younger than T2 (Kurtz et al. 1994;Ghosh et al. 2000). Using the James Clerk Maxwell Telescope (JCMT) 850 m dust continuum map, both the sites T1 and T2 were found to be connected by a filamentary feature (see Figure 1 around IRAS 06056+2131 and IRAS 06058+2138 in Klein et al. 2005). ...
We present a multi-scale and multi-wavelength study to unveil massive star formation (MSF) processes around sites AFGL 5180, and AFGL 6366S, both hosting a Class II 6.7 GHz methanol maser emission. The radio continuum map at 8.46 GHz reveals a small cluster of radio sources toward AFGL 5180. Signatures of the early stages of MSF in our target sites are spatially seen at the opposite edges of a filamentary cloud (length 5 pc), which is observed in the sub-millimeter dust continuum maps. Using the near-infrared photometric data, the spatial distribution of young stellar objects is found toward the entire filament, primarily clustered at its edges. The getsf utility on the Herschel far-infrared images reveals a hub-filament system (HFS) toward each target site. The analysis of the molecular line data, which benefits from large area coverage (1 degree 1 degree), detects two cloud components with a connection in both position and velocity space. This supports the scenario of a cloud-cloud collision (CCC) that occurred 1 Myr ago. The filamentary cloud, connecting AFGL 5180 and AFGL 6366S, seems spatially close to an HII region Sh2-247 excited by a massive O9.5 star. Based on the knowledge of various pressures exerted by the massive star on its surroundings, the impact of its energetic feedback on the filamentary cloud is found to be insignificant. Overall, our observational outcomes favor the possibility of the CCC scenario driving MSF and the formation of HFSs toward the target sites.
... Although still lacking accurate astrometric measurements, a much younger star-forming dense clump with an embedded stellar cluster and at least one compact H II region (named Sh2-157B) and associated water masers has been found to be associated with Sh2-157 (Chen et al. 2009 ). This is located less than 1 arcmin from the south-west (Kurtz, Churchwell & Wood 1994Chen et al. 2012 ) of the optical nebula. The evidence presented abo v e clearly indicates that Sh2-157A, Sh2-157B, IRAS 23139 + 5939, 2MASS 23161503 + 5954332, and probably also IRAS 23139 + 5943 (see Fig. 1 ) are all components of the same star formation complex that, as will be discussed in Section 4 , has had several recent episodes of star formation. ...
The far-infrared source IRAS 23139+5939 (G111.25-0.77) is a well-studied massive star-forming region at the centre of a dense molecular clump. It is associated with a low-luminosity and variable methanol maser, a number of water maser clusters, and several compact HII regions. We present new sub-arcsec resolution broad- and narrow-band near- and mid-infrared calibrated images. These were analysed together with WISE images and longer wavelength published data. We establish that IRAS 23139+5939 is a multiple massive young stellar object with a SED characteristic of a Class I object. Its deeply embedded (AV = 21) central young stellar objects have a total luminosity 3 × 104L⊙ and a mass of 16 M⊙. We find several small knots of H2 emission in its vicinity, bordering a large CO outflow driven by the protostar. Their distribution suggests the presence of several YSOs with jets. A young embedded stellar cluster of size ∼40″ (0.65 pc) is found around the massive protostar, with evidence of protoplanetary discs in more than 50 per cent of the likely members. We also report a large arc of H2 emission surrounding a nearby Hα emission star displaying a large infrared-excess, with a total luminosity of 1.5 × 103L⊙. Gaia DR3 and VLBI parallaxes indicate a common distance of 3.34 kpc to these two young stellar objects, a distance similar to that to Sh2-157, a nearby massive star-forming region, which appears connected to IRAS 23139+5939 by a warm dust filament.
... The youngest massive YSOs are thought to be embedded in the very small and dense H II regions, called ultra-compact H II regions with sizes smaller than 0.1 pc and densities greater than 10 4 cm −3 , and the hyper-compact H II regions with even smaller sizes ∼0.03 pc and higher densities ∼10 6 cm −3 . These ultra-and hyper-compact H II regions are so dense that the central YSOs cannot be detected optically (Wood & Churchwell 1989;Kurtz et al. 1994;Hoare et al. 2007). Roughly half of YSOs in our samples have compact H II regions smaller than 1 pc, but their densities estimated from the [S II] lines are not as high as those of ultra-compact H II regions. ...
We present low-resolution optical spectra and classifications of 92 blue objects with mid-infrared excesses in the Large Magellanic Cloud. The majority of these objects were selected with the criteria of U − B < 0 and V < 17 from the potential young stellar object (YSO) candidates in Gruendl & Chu (GC09), which were identified based on Spitzer Infrared Array Camera and Multiband Imaging Photometer for Spitzer observations in conjunction with optical photometry from the Magellanic Clouds Photometric Survey. Many of the sample objects have ambiguous classifications. We examined the properties of these 92 objects using low-resolution optical spectra obtained with the SOAR 4.1 m Telescope at Cerro Pachon and the Blanco 4 m Telescope at Cerro Tololo Inter-American Observatory, supplemented by available photometric and imaging observations. We estimated the spectral types, temperatures, and luminosities of these objects from the optical to near-IR spectral energy distributions based on the photometric data, and further examined stellar absorption line features in the optical spectra to verify the spectral types. The interstellar/circumstellar environments, assessed from nebular line imaging observations and nebular lines detected in the stellar spectra, further helped constrain the nature of stars. Among these 92 objects, we confirm 42 stars as YSOs, and the remaining 50 objects as protoplanetary nebulae, post-AGB/RGB stars, blue evolved massive stars, stars with dust in vicinity, or uncertain classifications. Our results show that the photometric criteria in GC09 are generally effective in the initial selection of YSO candidates, and the low-resolution spectroscopy combined with environment assessment can be useful to better constrain the classifications and ameliorate most ambiguities.
... Its structure and size indicate that this is likely an ultracompact (UC) H II region. Following the formulae in Kurtz et al. (1994) and the tabulation in Panagia (1973), we find that the ionizing star is consistent with a zero-age main sequence B3-type star. ...
We report Very Large Array observations in the Q band toward 10 ionized jet candidates to search for SiO emission, a well-known shocked gas tracer. We detected 7 mm continuum counterparts toward 90% of the jet candidates. In most cases, the jet candidate is located toward the center of the 7 mm core, and the high masses (≈100 M ⊙ ) and densities (≈10 ⁷ cm ⁻³ ) of the cores suggest that the central objects are very young high-mass protostars. We detected SiO J = 1–0 emission associated with six target sources. In all cases, the morphology and spectrum of the emission is consistent with what is expected for molecular jets along an outflow axis, thus confirming the jet nature of 60% of our sample. Our data suggest a positive correlation between the SiO luminosity L SiO , and both the bolometric luminosity L Bol and the radio luminosity S ν d ² of the driving sources.
... Its structure and size indicate that this is likely an Ultra-Compact (UC) H II region. Following the formulae in Kurtz et al. (1994) and the tabulation in Panagia (1973), we find that the ionizing star is consistent with a ZAMS B3 type star. ...
We report Very Large Array (VLA) observations in the Q-band toward 10 ionized jet candidates to search for SiO emission, a well-known shocked gas tracer. We detected 7 mm continuum counterparts toward 90% of the jet candidates. In most cases, the jet candidate is located toward the center of the 7 mm core, and the high masses () and densities () of the cores suggest that the central objects are very young high-mass protostars. We detected SiO emission associated with 6 target sources. In all cases, the morphology and spectrum of the emission is consistent with what is expected for molecular jets along an outflow axis, thus confirming the jet nature of 60% of our sample. Our data suggest a positive correlation between the SiO luminosity , and both the bolometric luminosity and the radio luminosity of the driving sources.
... They are identified accordingly. Kurtz et al. (1994) measured the ratio of 100 m to 2 cm (15 GHz) flux densities and found it lies in the range 1000-400000, with no UCH regions having 100 / 2cm < 1000. Following PIRXV we use this relation to put limits on the 15 GHz maximum flux densities that could be emitted by candidate UCH regions encountered in the apertures used for measuring the flux densities of our sample of sources. ...
The QUIJOTE-MFI Northern Hemisphere Wide-Survey has provided maps of the sky above declinations at 11, 13, 17 and 19GHz. These data are combined with ancillary data to produce Spectral Energy Distributions in intensity in the frequency range 0.4--3\,000GHz on a sample of 52 candidate compact sources harbouring anomalous microwave emission (AME). We apply a component separation analysis at 1 scale on the full sample from which we identify 44 sources with high AME significance. We explore correlations between different fitted parameters on this last sample. QUIJOTE-MFI data contribute to notably improve the characterisation of the AME spectrum, and its separation from the other components. In particular, ignoring the 10--20\,GHz data produces on average an underestimation of the AME amplitude, and an overestimation of the free-free component. We find an average AME peak frequency of 23.6 3.6GHz, about 4GHz lower than the value reported in previous studies. The strongest correlation is found between the peak flux density of the thermal dust and of the AME component. A mild correlation is found between the AME emissivity () and the interstellar radiation field. On the other hand no correlation is found between the AME emissivity and the free-free radiation Emission Measure. Our statistical results suggest that the interstellar radiation field could still be the main driver of the intensity of the AME as regards spinning dust excitation mechanisms. On the other hand, it is not clear whether spinning dust would be most likely associated with cold phases of the interstellar medium rather than with hot phases dominated by free-free radiation.
... Now, there is no standard way to extrapolate these flux densities to the peak frequency of our AME detection. Nonetheless, we can refer to the SEDs plotted in Kurtz et al. (1994) for several different UCHII regions, which were built using VLA integrated flux density measurements at 8.3 and 15 GHz in combination with IRAS flux densities and other ancillary data. The plots do not show any appreciable variation of the spectrum for frequencies 100 GHz. ...
We present new intensity and polarisation maps obtained with the QUIJOTE experiment towards the Galactic regions W49, W51 and IC443, covering the frequency range from 10 to 20 GHz at 1 deg angular resolution, with a sensitivity in the range 35-79 K/beam for total intensity and 13-23 K/beam for polarisation. For each region, we combine QUIJOTE maps with ancillary data at frequencies ranging from 0.4 to 3000 GHz, reconstruct the spectral energy distribution and model it with a combination of known foregrounds. We detect anomalous microwave emission (AME) in total intensity towards W49 at 4.7 and W51 at 4.0 with peak frequencies = (20.0 1.4) GHz and = (17.7 3.6) GHz respectively; this is the first detection of AME towards W51. The contamination from ultra-compact HII regions to the residual AME flux density is estimated at 10% in W49 and 5% in W51, and does not rule out the AME detection. The polarised SEDs reveal a synchrotron contribution with spectral indices = -0.67 0.10 in W49 and = -0.51 0.07 in W51, ascribed to the diffuse Galactic emission and to the local supernova remnant respectively. Towards IC443 in total intensity we measure a broken power-law synchrotron spectrum with cut-off frequency = (114 73) GHz, in agreement with previous studies; our analysis, however, rules out any AME contribution which had been previously claimed towards IC443. No evidence of polarised AME emission is detected in this study.
... They are identified accordingly. Kurtz et al. (1994) measured the ratio of 100 m to 2 cm (15 GHz) flux densities and found it lies in the range 1000-400000, with no UCH regions having 100 / 2cm < 1000. Following PIRXV we use this relation to put limits on the 15 GHz maximum flux densities that could be emitted by candidate UCH regions encountered in the apertures used for measuring the flux densities of our sample of sources. ...
The QUIJOTE-MFI Northern Hemisphere Wide Survey has provided maps of the sky above declinations −30° at 11, 13, 17, and 19 GHz. These data are combined with ancillary data to produce Spectral Energy Distributions in intensity in the frequency range 0.4–3 000 GHz on a sample of 52 candidate compact sources harbouring anomalous microwave emission (AME). We apply a component separation analysis at 1° scale on the full sample from which we identify 44 sources with high AME significance. We explore correlations between different fitted parameters on this last sample. QUIJOTE-MFI data contribute to notably improve the characterization of the AME spectrum, and its separation from the other components. In particular, ignoring the 10–20 GHz data produces on average an underestimation of the AME amplitude, and an overestimation of the free–free component. We find an average AME peak frequency of 23.6 ± 3.6 GHz, about 4 GHz lower than the value reported in previous studies. The strongest correlation is found between the peak flux density of the thermal dust and of the AME component. A mild correlation is found between the AME emissivity (AAME/τ250) and the interstellar radiation field. On the other hand no correlation is found between the AME emissivity and the free–free radiation Emission Measure. Our statistical results suggest that the interstellar radiation field could still be the main driver of the intensity of the AME as regards spinning dust excitation mechanisms. On the other hand, it is not clear whether spinning dust would be most likely associated with cold phases of the interstellar medium rather than with hot phases dominated by free–free radiation.
... Now, there is no standard way to extrapolate these flux densities to the peak frequency of our AME detection. Nonetheless, we can refer to the SEDs plotted in Kurtz et al. (1994) for several different UCHII regions, which were built using VLA integrated flux density measurements at 8.3 and 15 GHz in combination with IRAS flux densities and other ancillary data. The plots do not show any appreciable variation of the spectrum for frequencies 100 GHz. ...
We present new intensity and polarization maps obtained with the QUIJOTE experiment towards the Galactic regions W49, W51 and IC443, covering the frequency range from 10 to 20 GHz at angular resolution, with a sensitivity in the range 35–79 for total intensity and 13–23 for polarization. For each region, we combine QUIJOTE maps with ancillary data at frequencies ranging from 0.4 to 3000 GHz, reconstruct the spectral energy distribution and model it with a combination of known foregrounds. We detect anomalous microwave emission (AME) in total intensity towards W49 at 4.7σ and W51 at 4.0σ with peak frequencies and , respectively; this is the first detection of AME towards W51. The contamination from ultracompact H ii regions to the residual AME flux density is estimated at 10 per cent in W49 and 5 per cent in W51, and does not rule out the AME detection. The polarized SEDs reveal a synchrotron contribution with spectral indices αs = −0.67 ± 0.10 in W49 and αs = −0.51 ± 0.07 in W51, ascribed to the diffuse Galactic emission and to the local supernova remnant, respectively. Towards IC443 in total intensity we measure a broken power-law synchrotron spectrum with cut-off frequency , in agreement with previous studies; our analysis, however, rules out any AME contribution which had been previously claimed towards IC443. No evidence of polarized AME emission is detected in this study.
... Second, the relatively high frequency is ideal for quantifying star formation based on the level of freefree emission present (e.g., Murphy et al. 2010). At lower radio frequencies (∼1 GHz and below) ultracompact H II (UCHII) regions are optically thick and therefore go undetected, while at 30 GHz the majority of sources will be in the optically thin regime (e.g., Kurtz et al. 1994). Third, AME, which is thought to be primarily due to spinning dust emission , has a peaked spectrum near 30 GHz. ...
We present early results from the CO Mapping Array Project (COMAP) Galactic Plane Survey conducted between 2019 June and 2021 April, spanning 20° < ℓ < 40° in Galactic longitude and ∣ b ∣ < 1.°5 in Galactic latitude with an angular resolution of 4.′5. We present initial results from the first part of the survey, including the diffuse emission and spectral energy distributions of H ii regions and supernova remnants (SNRs). Using low- and high-frequency surveys to constrain free–free and thermal dust emission contributions, we find evidence of excess flux density at 30 GHz in six regions, which we interpret as anomalous microwave emission. Furthermore we model ultracompact H ii contributions using data from the 5 GHz CORNISH catalog and reject these as the cause of the 30 GHz excess. Six known SNRs are detected at 30 GHz, and we measure spectral indices consistent with the literature or show evidence of steepening. The flux density of the SNR W44 at 30 GHz is consistent with a power-law extrapolation from lower frequencies with no indication of spectral steepening in contrast with recent results from the Sardinia Radio Telescope. We also extract five hydrogen radio recombination lines (RRLs) to map the warm ionized gas, which can be used to estimate electron temperatures or to constrain continuum free–free emission. The full COMAP Galactic Plane Survey, to be released in 2023/2024, will span ℓ ∼ 20°–220° and will be the first large-scale radio continuum and RRL survey at 30 GHz with 4.′5 resolution.
... Multi-wavelength Very Large Array (VLA) observations identified nine radio continuum sources (denoted A-I) in this region (Garay et al. 1993 ;Testi et al. 2000 ). The extended H II region 'A', cometary-shaped H II region 'B', and compact H II region 'C' are three evolved H II regions (Kurtz, Churchwell & Wood 1994 ). James Clerk Maxwell Telescope (JCMT)/Submillimetre Common-User Bolometer Array (SCUBA) 450-μm observations found that new generations of high-mass young stellar objects ('G9.62 clump') are forming in the region located to the east of the evolved H II regions (Liu et al. 2011(Liu et al. , 2017. ...
Investigating the physical and chemical structures of massive star-forming regions is critical for understanding the formation and the early evolution of massive stars. We performed a detailed line survey toward six dense cores named as MM1, MM4, MM6, MM7, MM8, and MM11 in G9.62+0.19 star-forming region resolved in ALMA band 3 observations. Toward these cores, about 172 transitions have been identified and attributed to 16 species including organic Oxygen-, Nitrogen-, Sulfur-bearing molecules and their isotopologues. Four dense cores MM7, MM8, MM4, and MM11 are line rich sources. Modeling of these spectral lines reveals the rotational temperature in a range of 72−115 K, 100−163 K, 102−204 K, and 84−123 K for the MM7, MM8, MM4, and MM11, respectively. The molecular column densities are 1.6 × 1015–9.2 × 1017 cm−2 toward the four cores. The cores MM8 and MM4 show chemical difference between Oxygen- and Nitrogen-bearing species, i.e. MM4 is rich in oxygen-bearing molecules while nitrogen-bearing molecules especially vibrationally excited HC3N lines are mainly observed in MM8. The distinct initial temperature at accretion phase may lead to this N/O differentiation. Through analyzing column densities and spatial distributions of O-bearing Complex Organic Molecules (COMs), we found that C2H5OH and CH3OCH3 might have a common precursor, CH3OH. CH3OCHO and CH3OCH3 are likely chemically linked. In addition, the observed variation in HC3N and HC5N emission may indicate that their different formation mechanism at hot and cold regions.
... The source systemic velocity is v sys = 95.6 ± 0.5 km s −1 . We note that some previ-ous studies adopted a larger distance of 9.1 kpc (Kurtz et al. 1994;de la Fuente et al. 2020). Within a radius of 0.48 pc, G28.20-0.05 has been estimated to have a gas mass of 33 M , and thus a mass surface density of 9.52 × 10 −3 g cm −2 based on SMA 1.3 mm continuum data (Hernández-Hernández et al. 2014). ...
We report high-resolution 1.3mm continuum and molecular line observations of the massive protostar G28.20-0.05 with ALMA. The continuum image reveals a ring-like structure with 2,000 au radius, similar to morphology seen in archival 1.3cm VLA observations. Based on its spectral index and associated H30 emission, this structure mainly traces ionized gas. However, there is evidence for 30 M of dusty gas near the main mm continuum peak on one side of the ring, as well as in adjacent regions within 3,000 au. A virial analysis on scales of 2,000 au from hot core line emission yields a dynamical mass of 80M. A strong velocity gradient in the H30 emission is evidence for a rotating, ionized disk wind, which drives a larger-scale molecular outflow. An infrared SED analysis indicates a current protostellar mass of m24 M forming from a core with initial mass in a clump with mass surface density of . Thus the SED and other properties of the system can be understood in the context of core accretion models. Structure-finding analysis on the larger-scale continuum image indicates G28.20-0.05 is forming in a relatively isolated environment, with no other concentrated sources, i.e., protostellar cores, above 1 M found from 0.1 to 0.4 pc around the source. This implies that a massive star is able to form in relative isolation and the dearth of other protostellar companions within the 1 pc environs is a strong constraint on massive star formation theories that predict the presence of a surrounding protocluster.
Several powerful flare events have been recorded because of long-term monitoring on the RT-22 radio telescope (Simeiz) of the galactic source G25.65+1.05 from 2000 to 2024. The amplitude of the most powerful flare increased rapidly and reached a record level for this source of 130 kJy. The orbital (7.5 years) and precessional (60 years) periods in the binary system of massive O5 class stars responsible for the occurrence of flares based on monitoring data have been presumably determined. Individual short flares, lasting no more than a month, presumably belonged to a maser in an unsaturated state. The shape of the central part of the maser line, near the maximum phase, suggests a single-component source responsible for the bulk of the increase in flux density. Thus, the most powerful kilomaser G25.65+1.05 in the water vapor line at frequency 22.2 GHz has been registered in the Galaxy. The possibility of detecting gravitational waves (GWs) coming from the massive stellar binary system is considered.
The active galactic nucleus S 0528+134 was discovered in a search survey at a frequency of 8550 MHz in 1969 using the radio telescope RT-22 (Simeiz) at the Crimean Astrophysical Observatory—the study aimed to search for new active galactic nuclei (AGN). In this article, the goal was to determine the physical characteristics of the close binary system S 0528+134 for the subsequent assessment of the level of gravitational radiation coming from it. During long-term monitoring of the object at a frequency of 8 GHz, some powerful flares of flux density occurred, which made it possible to consider the source the most powerful emitter in the Universe. The presence of selected harmonic components in the flux density variations of S 0528+134 allowed obtaining the main physical characteristics of a binary system of supermassive black holes (SMBHs), which placed S 0528+134 in the rank of one of the most massive SMBHs. This AGN can also be considered the most powerful source for detecting GWs by using International Pulsar Timing Array gravitational wave detectors.
Context . H II regions are the signposts of massive ( M ≥ 8 M ⊙ ) star-forming sites in our Galaxy. It has been observed that the ionizing photon rate inferred from the radio continuum emission of H II regions is significantly lower (~90%) than that inferred from far-infrared fluxes measured by the Infrared Astronomical Satellite.
Aims . This discrepancy in the ionizing photon rates may arise due to there being significant amounts of dust within the H II regions or the presence of extended emission that is undetected by high-resolution radio interferometric observations. Here, we study a sample of eight compact and ultracompact H II regions with extended emission to explore its role in resolving the discrepancy.
Methods . We have used observations at the upgraded Giant Metrewave Radio Telescope (1.25–1.45 GHz) and data from the GLOSTAR survey (4–8 GHz) to estimate the ionizing photon rate from the radio continuum emission. We have also estimated the ionizing photon rate from the infrared luminosity by fitting a spectral energy distribution function to the infrared data from the Spitzer- GLIMPSE, MIPSGAL, and Hi-GAL surveys. The excellent sensitivity of the radio observations to extended emission allows us to investigate the actual fraction of ionizing photons that are absorbed by dust in compact and ultracompact H II regions.
Results . Barring one source, we find a direct association between the radio continuum emission from the compact and diffuse components of the H II region. Our study shows that the ionizing photon rates estimated using the radio and infrared data are within reasonable agreement (5–28%) if we include the extended emission. We also find multiple candidate ionizing stars in all our sources, and the ionizing photon rates from the radio observations and candidate stars are in reasonable agreement.
In this study we present 18-24 GHz and high-angular-resolution (0.5 arcsec) radio wavelength Australia Telescope Compact Array (ATCA) follow-up observations towards a sample of 39 HC H ii region candidates. These objects, taken from a sample hosting 6.7 GHz methanol masers, were chosen due to the compact and optically thick nature of their continuum emission. We have detected 27 compact radio sources and constructed their spectral energy distributions (SEDs) over the 5–24 GHz range to determine the young H ii region’s physical properties, i.e., diameter, electron density ne, emission measure, Lyman continuum flux NLy and turnover frequency νt. The flux measurements are fitted for 20 objects assuming an ionisation-bounded H ii region with uniform density model. For the remaining 7 objects that lack constraints spanning both their optically thick and thin regimes, we utilise relations from the literature to determine their physical properties. Comparing these determined parameters with those of known hypercompact (HC) and ultracompact (UC) H ii regions, we have identified 13 HC H ii regions, 6 intermediate objects that fall between HC H ii and UC H ii regions, 6 UC H ii regions and one radio jet candidate which increases the known population of HC H ii regions by ∼50 per cent. All the young and compact H ii regions are embedded in dusty and dense clumps and ∼80 per cent of the HC H ii regions identified in this work are associated with various maser species (CH3OH, H2O and OH). Four of our radio sources remain optically thick at 24 GHz; we consider these to be amongst the youngest HC H ii regions.
Aims. We aim to identify and characterize cores in the high-mass protocluster W49A, determine their evolutionary stages, and measure the associated lifetimes.
Methods. We built a catalog of 129 cores extracted from an ALMA 1.3 mm continuum image at 0.26″ (2900 au) angular resolution. The association between cores and hypercompact or ultracompact H II (H/UC H II ) regions was established from the analysis of VLA 3.3 cm continuum and H30 α line observations. We also looked for emission of hot molecular cores (HMCs) using the methyl formate doublet at 218.29 GHz.
Results. We identified 40 cores associated with an H/UC H II region and 19 HMCs over the ALMA mosaic. The 52 cores with an H/UC H II region and/or an HMC are assumed to be high-mass protostellar cores, while the rest of the core population likely consists of prestellar cores and low-mass protostellar cores. We found a good agreement between the two tracers of ionized gas, with 23 common detections and only four cores detected at 3.3 cm and not in H30 α . The spectral indexes from 3.3 cm to 1.3 mm range from 1, for the youngest cores with partially optically thick free-free emission, to about −0.1, which is for the optically thin free-free emission obtained for cores that are likely more evolved.
Conclusions. Using the H/UC H II regions as a reference, we found the statistical lifetimes of the HMC and massive protostellar phases in W49N to be about 6 × 10 ⁴ yr and 1.4 × 10 ⁵ yr, respectively. We also showed that HMCs can coexist with H/UC H II regions during a short fraction of the core lifetime, about 2 × 10 ⁴ yr. This indicates a rapid dispersal of the inner molecule envelope once the HC H II is formed.
We present results of the study of maser emission variability in the 1665 MHz OH line in the G43.8–0.1 star formation region based on observations (monitoring) in 2008–2022 at the Large Radio Telescope in Nancy (France). Variability of all polarization parameters of the majority of spectral features, which has a monotonic regular character, has been found. Spatial identification of the main spectral features of the OH 1665 MHz line with maser spots (condensations) on the VLA map has been carried out. For the Zeeman pair VLSR=44.15 km/s, a monotonic change of the splitting with time during 2008–2022 was found and, consequently, a change of the magnitude of the longitudinal magnetic field. According to our calculations, at the end of 2012, the direction of the magnetic field changed to the opposite. Сorrelated with H∥, there were changes in the angle χ and, as a consequence, changes in the direction of the vector of the transverse magnetic field H⊥0. For the maser feature at 44.5 km/s, a change of H⊥ by 180° was found. In 2016–2022, some reorientation of the global magnetic field (H⊥) in G43.8–0.1 occurred. The field became less chaotic: in the eastern part, the field in maser condensations is perpendicular to the arc, and in the western part, it is parallel to the arc. It is assumed that the global magnetic field in the entire U H II region of the G43.8–0.1 source has the same direction: along the axis (northeast)—(southwest).
Context . The fragmentation of high-mass star-forming regions depends on a variety of physical parameters, including density, the magnetic field, and turbulent gas properties.
Aims . We evaluate the importance of the density and magnetic field structures in relation to the fragmentation properties during high-mass star formation.
Methods . Observing the large parsec-scale Stokes I millimeter dust continuum emission with the IRAM 30 m telescope and the intermediate-scale (<0.1 pc) polarized submillimeter dust emission with the Submillimeter Array toward a sample of 20 high-mass star-forming regions allows us to quantify the dependence of the fragmentation behavior of these regions on the density and magnetic field structures.
Results . Based on the IRAM 30 m data, we infer density distributions n ∝ r − p of the regions with typical power-law slopes p around ~1.5. There is no obvious correlation between the power-law slopes of the density structures on larger clump scales (~1 pc) and the number of fragments on smaller core scales (<0.1 pc). Comparing the large-scale single-dish density profiles to those derived earlier from interferometric observations at smaller spatial scales, we find that the smaller-scale power-law slopes are steeper, typically around ~2.0. The flattening toward larger scales is consistent with the star-forming regions being embedded in larger cloud structures that do not decrease in density away from a particular core. The magnetic fields of several regions appear to be aligned with filamentary structures that lead toward the densest central cores. Furthermore, we find different polarization structures; some regions exhibit central polarization holes, whereas other regions show polarized emission also toward the central peak positions. Nevertheless, the polarized intensities are inversely related to the Stokes I intensities, following roughly a power-law slope of ∝ S I −0.62 . We estimate magnetic field strengths between ~0.2 and ~4.5 mG, and we find no clear correlation between magnetic field strength and the fragmentation level of the regions. A comparison of the turbulent to magnetic energies shows that they are of roughly equal importance in this sample. The mass-to-flux ratios range between ~2 and ~7, consistent with collapsing star-forming regions.
Conclusions . Finding no clear correlations between the present-day large-scale density structure, the magnetic field strength, and the smaller-scale fragmentation properties of the regions, indicates that the fragmentation of high-mass star-forming regions may not be affected strongly by the initial density profiles and magnetic field properties. However, considering the limited evolutionary range and spatial scales of the presented CORE analysis, future research directions should include density structure analysis of younger regions that better resemble the initial conditions, as well as connecting the observed intermediate-scale magnetic field structure with the larger-scale magnetic fields of the parental molecular clouds.
Context . The infrared dark cloud (IRDC) G14.225-0.506 is part of the extended and massive molecular cloud located to the southwest of the H II region M17. The cloud is associated with a network of filaments, which result in two different dense hubs, as well as with several signposts of star formation activity and a rich population of protostars and young stellar objects (YSOs).
Aims . The aim of this work is to study the centimeter continuum emission in order to characterize the stellar population in both regions, as well as to study the evolutionary sequence across the IRDC G14.225-0.506.
Methods . We performed deep (~ 1.5–3 μJy) radio continuum observations at 6 and 3.6 cm toward the IRDC G14.225-0.506 using the Karl G. Jansky Very Large Array (VLA) in its most extended A configuration (~0.3″). Data at both C and X bands were imaged using the same ( u,v ) range in order to derive spectral indices. We have also made use of observations taken during different days to study the presence of variability at short timescales toward the detected sources.
Results . We detected a total of 66 sources, 32 in the northern region G14.2-N and 34 in the southern region G14.2-S. Ten of the sources are found to be variable, with three located in G14.2-N and seven in G14.2-S. Based on their spectral index, the emission in G14.2-N is mainly dominated by nonthermal sources while G14.2-S contains more thermal emitters. Approximately 75% of the sources present a counterpart at other wavelengths. When considering the inner 0.4 pc region around the center of each hub, the number of infrared (IR) sources in G14.2-N is larger than in G14.2-S by a factor of 4. We also studied the relation between the radio luminosity and the bolometric luminosity, finding that the thermal emission of the studied sources is compatible with thermal radio jets. For our sources with X-ray counterparts, the nonthermal emitters follow a Güdel-Benz relation with κ = 0.03, as previously suggested for other similar regions.
Conclusions . We found similar levels of fragmentation between G14.2-N and G14.2-S, suggesting that both regions are most likely twin hubs. The nonthermal emission found in the less evolved objects, mainly coming from G14.2-N, suggests that G14.2-N may be composed of more massive YSOs as well as being in a more advanced evolutionary stage, consistent with the “filament-halo” gradient in age and mass from previous works. Overall, our results confirm a wider evolutionary sequence from the southwest to northeast starting in G14.2-S as the youngest part, followed by G14.2-N, and ending with the most evolved region M17.
Aims. The application of silicon monoxide (SiO) as a shock tracer arises from its propensity to occur in the gas phase as a result of shock-induced phenomena, including outflow activity and interactions between molecular clouds and expanding H II regions or supernova remnants. For this work, we searched for indications of shocks toward 366 massive star-forming regions by observing the ground rotational transition of SiO ( v = 0, J = 1-0) at 43 GHz with the Korean VLBI Network (KVN) 21 m telescopes to extend our understanding on the origins of SiO in star-forming regions.
Methods. We analyzed the thermal SiO 1-0 emission and compared the properties of SiO emission with the physical parameters of associated massive dense clumps as well as 22 GHz H 2 O and Class I 44 GHz CH 3 OH maser emission.
Results. We detected SiO emission toward 104 regions that consist of 57 IRDCs, 21 HMPOs, and 26 UCH II s. Out of 104 sources, 71 and 80 sources have 22 GHz H 2 O and 44 GHz Class I CH 3 OH maser counterparts, respectively. The determined median SiO column density, N (SiO), and abundance, X (SiO), relative to N (H 2 ) are 8.12 × 10 ¹² cm ⁻² and 1.28 × 10 ⁻¹⁰ , respectively. These values are similar to those obtained toward other star-forming regions and also consistent with predicted values from shock models with low-velocity shocks (≲ 10–15 km s ⁻¹ ). For sources with dust temperatures of ( T dust ) ≲ 20 K, we find that N (SiO) and X (SiO) derived with the J = 1–0 transition are a factor ~3 larger than those from the previous studies obtained with SiO 2–1. While the X (SiO) does not exhibit any strong correlation with the evolutionary stages of their host clumps, L SiO is highly correlated with dust clump mass, and L SiO / L bol also has a strong negative correlation with T dust . This shows that colder and younger clumps have high L SiO / L bol suggestive of an evolutionary trend. This trend is not due to excess emission at higher velocities, such as SiO wing features, as the colder sources with high L SiO / L bol ratios lack wing features. Comparing SiO emission with H 2 O and Class I CH 3 OH masers, we find a significant correlation between L SiO / L bol and {{{L_{{\rm{C}}{{\rm{H}}_3}{\rm{OH}}}}} \mathord{\left/ {\vphantom {{{L_{{\rm{C}}{{\rm{H}}_3}{\rm{OH}}}}} {{L_{{\rm{bol}}}}}}} \right. \kern-\nulldelimiterspace} {{L_{{\rm{bol}}}}}} ratios, whereas no similar correlation is seen for the H 2 O maser emission. This suggests a similar origin for the SiO and Class I CH 3 OH emission in these sources.
Conclusions. We demonstrate that in cold regions SiO J = 1–0 may be a better tracer of shocks than a higher J transition of SiO. Lower T dust (and so probably less globally evolved) sources appear to have higher L SiO relative to their L bol . The SiO 1–0 emission toward infrared dark sources ( T dust ≲ 20 K), which do not contain identified outflow sources, may be related to other mechanisms producing low-velocity shocks (5–15 km s ⁻¹ ) for example, arising from cloud-cloud collisions, shocks triggered by expanding H II regions, global infall, or converging flows.
Class II CH3OH masers are used as a convenient tracer of disc-like structures in high-mass star formation. However, more than half of them show a complex distribution in Very Long Baseline Interferometry (VLBI) maps. The origin of such a complex distribution is still unknown. We conducted VLBI monitoring observations to unveil the origin of a complex class II CH3OH maser in the high-mass star-forming region G59.783+0.065. We observed the CH3OH maser at 6.7 GHz and the H2O maser at 22 GHz to probe detailed circumstellar kinematics and structures by the Japanese VLBI network and the VLBI Exploration of Radio Astrometry. We found similar bipolar distributions in both masers, specifically two clusters located 2000 au apart along the East-West direction. We detected a linear distribution of CH3OH masers in the Western cluster. A position-velocity diagram shows that the Western CH3OH masers trace a rotating disc-wind or infalling component inside an edge-on disc-like structure. In contrast to the simple bipolar expanding motions of the H2O masers, the CH3OH masers exhibited complex motions despite their spatial coincidence. Some of the Eastern CH3OH masers showed bipolar expansions similar to the H2O masers, while others displayed random or even inward motions. Such complex kinematics and their close association with the H2O maser could occur at the boundary between outflow and inflow. We suggest that the complex distribution of class II CH3OH masers, like G59.783+0.065 arises from several distinct circumstellar structures that simultaneously achieve maser excitation.
Context. Cygnus X is one of the closest and most active high-mass star-forming regions in our Galaxy, making it one of the best laboratories for studying massive star formation.
Aims. We aim to investigate the properties of molecular gas structures on different linear scales with the 4.8 GHz formaldehyde (H 2 CO) absorption line in Cygnus X.
Methods. As part of the GLOSTAR Galactic plane survey, we performed large-scale (7º×3º) simultaneous H 2 CO (1 1,0 –1 1,1 ) spectral line and radio continuum imaging observations toward Cygnus X at λ ~6 cm with the Karl G. Jansky Very Large Array and the Effelsberg 100 m radio telescope. We used auxiliary HI, ¹³ CO (1–0), dust continuum, and dust polarization data for our analysis.
Results. Our Effelsberg observations reveal widespread H 2 CO (1 1,0 –1 1,1 ) absorption with a spatial extent of ≳50 pc in Cygnus X for the first time. On large scales of 4.4 pc, the relative orientation between the local velocity gradient and the magnetic field tends to be more parallel at H 2 column densities of ≳1.8×10 ²² cm ⁻² . On the smaller scale of 0.17 pc, our VLA+Effelsberg combined data reveal H 2 CO (1 1,0 –1 1,1 ) absorption only towards three bright H II regions. Our observations demonstrate that H 2 CO (1 1,0 –1 1,1 ) is optically thin in general. The kinematic analysis supports the assertion that molecular clouds generally exhibit supersonic motions on scales of 0.17−4.4 pc. We show a non-negligible contribution of the cosmic microwave background radiation to the extended absorption features in Cygnus X. Our observations suggest that H 2 CO (1 1,0 –1 1,1 ) can trace molecular gas with H 2 column densities of ≳5 × 10 ²¹ cm ⁻² (i.e., A V ≳ 5). The ortho-H 2 CO fractional abundance with respect to H 2 has a mean value of 7.0 × 10 ⁻¹⁰ . A comparison of the velocity dispersions on different linear scales suggests that the velocity dispersions of the dominant −3 km s ⁻¹ velocity component in the prominent DR21 region are nearly identical on scales of 0.17−4.4 pc, which deviates from the expected behavior of classic turbulence.
A H ii region is a kind of emission nebula, and more definite samples of H ii regions can help study the formation and evolution of galaxies. Hence, a systematic search for H ii regions is necessary. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) conducts medium-resolution spectroscopic surveys and provides abundant valuable spectra for unique and rare celestial body research. Therefore, the medium-resolution spectra of LAMOST are an ideal data source for searching for Galactic H ii regions. This study uses the LAMOST spectra to expand the current spectral sample of Galactic H ii regions through machine learning. Inspired by deep convolutional neural networks with wide first-layer kernels (WDCNN), a new spectral-screening method, multihead WDCNN, is proposed and implemented. Infrared criteria are further used for the identification of Galactic H ii region candidates. Experimental results show that the multihead WDCNN model is superior to other machine-learning methods and it can effectively extract spectral features and identify H ii regions from the massive spectral database. In the end, among all candidates, 57 H ii regions are identified and known in SIMBAD, and four objects are identified as “to be confirmed” Galactic H ii region candidates. The known H ii regions and H ii region candidates can be retrieved from the LAMOST website.
We present a multiscale and multiwavelength study to unveil massive star formation (MSF) processes around sites AFGL 5180 and AFGL 6366S, both hosting a Class ii 6.7 GHz methanol maser emission. The radio continuum map at 8.46 GHz reveals a small cluster of radio sources towards AFGL 5180. Signatures of the early stages of MSF in our target sites are spatially seen at the opposite edges of a filamentary cloud (length ∼5 pc), which is observed in the submillimetre dust continuum maps. Using the near-infrared photometric data, the spatial distribution of young stellar objects is found towards the entire filament, primarily clustered at its edges. The getsf utility on the Herschel far-infrared images reveals a hub–filament system (HFS) towards each target site. The analysis of the molecular line data, which benefits from large area coverage (∼1° × 1°), detects two cloud components with a connection in both position and velocity space. This supports the scenario of a cloud–cloud collision (CCC) that occurred ∼1 Myr ago. The filamentary cloud, connecting AFGL 5180 and AFGL 6366S, seems spatially close to an H ii region Sh 2−247 excited by a massive O9.5 star. Based on the knowledge of various pressures exerted by the massive star on its surroundings, the impact of its energetic feedback on the filamentary cloud is found to be insignificant. Overall, our observational outcomes favour the possibility of the CCC scenario driving MSF and the formation of HFSs towards the target sites.
Context. The G25.65+1.04 source is one of the few known ‘super-flare’ water masers in the Milky Way, but in contrast to other super-flare sources, it remains the least studied. In fact, even the nature of the source driving the water maser is still unclear.
Aims. With this project, we aim to clarify the composition and properties of the G25.65+1.04 region by means of examining the parameters of the continuum sources and establishing their association with masers of different types.
Methods. Our previous VLA ( Karl G. Jansky Very Large Array) observation detected four continuum peaks (VLA 1-4), three of which (VLA 1-3) were closely spaced and presented a linear orientation. However, the observation, which used the VLA B configuration, lacked the spatial resolution to resolve individual sources. A higher-resolution (A configuration) VLA observation of the continuum and spectral lines was conducted in 2019 using the L , S , C , and Ku bands.
Results. For the first time, the continuum source VLA 1 – associated with the flaring water maser – is resolved into two components: VLA 1A and 1B. The component VLA 1A and the water maser are found to spatially coincide and are thought to be powered by the same source, a protostar at an early stage of evolution showing active ejection. We argue that VLA 2 pinpoints an actively ejecting high-mass protostar, as it is associated with a 6.7 GHz methanol maser and a magnetised jet traced by a 22 GHz H 2 O maser. Highly polarised OH maser emission is detected in the vicinity of VLA 1-2, with the brightest OH maser found in VLA 2. The magnetic field, identified from the OH maser emission, ranges from ∼ + 0.4 mG in VLA 1A to ∼ − 8 mG in VLA 2.
Conclusions. The G25.65+1.04 region is found to consist of at least two young stellar objects: VLA 1A and VLA 2. Both sources are found to be at an active accretion and ejection stage of evolution.
Aims. Our main aims are to improve our understanding of the main properties of the radio source G316.8−0.1 (IRAS 14416−5937) where the DBS 89−90−91 embedded clusters are located, to identify the stellar population present in this region, and to study the interaction of these stars with the interstellar medium.
Methods. We analyzed some characteristics of the G316.8−0.1 radio source, consulting the SUMSS to study the radio continuum emission at 843 MHz and the H I SGPS at 21 cm. We also used photometric data at the JHK bands in the region of DBS 89−90−91 clusters obtained from the VVV survey and supplemented with the 2MASS catalogue. Our investigation of possible stars associated with the H II region was complemented with an astrometric analysis using the Gaia Early Data Release 3. To study the young stellar objects (YSOs), we consulted the mid-infrared photometric information from WISE, Spitzer −GLIMPSE Surveys, and the MSX point source catalog.
Results. The photometric and astrometric research carried out in the IRAS 14416−5937 region allowed us to improve our current understanding of the DBS 89−90−91 embedded clusters and their interaction with the interstellar medium. In the case of the cluster DBS 89, we identified 9 astrophotometric candidate members and 19 photometric candidate members, whereas for DBS 90−91 clusters we found 18 candidate photometric members. We obtained a distance value for DBS 89 linked to the radio source G316.8−0.1 of 2.9 ± 0.5 kpc. We also investigated 12 Class I YSO candidates, 35 Class II YSO candidates, 2 massive young stellar objects (MYSOs), and 1 compact ionized hydrogen (CHII) region distributed throughout the IRAS 14416−5937 region. Our analysis reveals that the G316.8−0.1 radio source is optically thin at frequencies ≥0.56 GHz. The H II regions G316.8−0.1−A and G316.8−0.1−B have similar radii and ionized hydrogen masses of ∼0.5 pc and ∼35 M ⊙ , respectively. The ionization parameter computed with the younger spectral types of adopted members of DBS 89 and DBS 90−91 clusters shows that they are able to generate the H II regions. The flux density of the H II region G316.8−0.1−B is lower than the flux density of the H II region G316.8−0.1−A.
Conclusions. We carried out a photometric and astrometric study, looking for members of the DBS 89−90−91 embedded clusters. We were able to identify the earliest stars of the clusters as the main exciting sources of the G316.8−0.1 radio source and have also estimated the main physical parameters of this source. We improve the current knowledge of the stellar components present in the Sagittarius-Carina arm of our Galaxy and its interaction with the interstellar medium.
The research of infall motion is a common means to study molecular cloud dynamics and the early process of star formation. Many works had been done in-depth research on infall. We searched the literature related to infall study of molecular cloud since 1994, summarized the infall sources identified by the authors. A total of 456 infall sources are catalogued. We classify them into high-mass and low-mass sources, in which the high-mass sources are divided into three evolutionary stages: prestellar, protostellar and {H\small II} region. \textbf{We divide the sources into clumps and cores according to their sizes.} The H column density values range from 1.21 10 to 9.75 10 cm, with a median value of 4.17 10 cm. The H column densities of high-mass and low-mass sources are significantly separated. % The H column density for low-mass stars is 10 cm, and for high-mass stars is about 10 cm 10 cm. The median value of infall velocity for high-mass \textbf{clumps} is \textbf{1.12} km s, and the infall velocities of low-mass \textbf{cores} are virtually all less than 0.5 km s. There is no obvious difference between different stages of evolution. The mass infall rates of low-mass \textbf{cores} are between 10 and 10 M, and those of high-mass \textbf{clumps} are between 10and 10M with only one exception. We do not find that the mass infall rates vary with evolutionary stages.
Context. Level population inversion of hydrogen atoms in ionized gas may lead to stimulated emission of hydrogen recombination lines, and the level populations can in turn be affected by powerful stimulated emissions.
Aims. In this work the interaction of the radiation fields and the level population inversion of hydrogen atoms is studied. The effect of the stimulated emissions on the line profiles is also investigated.
Methods. Our previous nl-model for calculating level populations of hydrogen atoms and hydrogen recombination lines is improved. The effects of line and continuum radiation fields on the level populations are considered in the improved model. By using this method the properties of simulated hydrogen recombination lines and level populations are used in analyses.
Results. The simulations show that hydrogen radio recombination lines are often emitted from the energy level with an inverted population. The widths of Hn α lines can be significantly narrowed by strong stimulated emissions to be even less than 10 km s ⁻¹ . The amplification of hydrogen recombination lines is more affected by the line optical depth than by the total optical depth. The influence of stimulated emission on the estimates of electron temperature and density of ionized gas is evaluated. We find that comparing multiple line-to-continuum ratios is a reliable method for estimating the electron temperature, while the effectiveness of the estimation of electron density is determined by the relative significance of stimulated emission.
Ultra-compact H ii (UC HII) regions are an important phase in the formation and early evolution of massive stars and a key component of the interstellar medium (ISM). The main objectives of this work are to study the young stellar population associated with the G45.07+0.13 and G45.12+0.13 UC HII regions, as well as the ISM in which they are embedded. We determined the distribution of the hydrogen column density (N( )) and dust temperature ( ) in the molecular cloud using Modified blackbody fitting on Herschel images obtained in four bands: 160, 250, 350, and 500\,\unicode{x03BC}\mathrm{m} . We used near-, mid-, and far-infrared photometric data to identify and classify the young stellar objects (YSOs). Their main parameters were determined by the radiation transfer models. We also constructed a colour-magnitude diagram and K luminosity functions (KLFs) to compare the parameters of stellar objects with the results of the radiative transfer models. We found that N( ) varies from to within the G45.07+0.13 and G45.12+0.13 regions, respectively. The maximum value is 35 K in G45.12+0.13 and 42 K in G45.07+0.13. then drops significantly from the centre to the periphery, reaching about 18–20 K at distances of and from InfraRed Astronomical Satellite (IRAS) 19110+1045 (G45.07+0.13) and IRAS 19111+1048 (G45.12+0.13), respectively. The gas plus dust mass value included in G45.12+0.13 is and in G45.07+0.13. The UC HII regions are connected through a cold ( ) bridge. The radial surface density distribution of the identified 518 YSOs exhibits dense clusters in the vicinity of both IRAS sources. The parameters of YSOs in the IRAS clusters (124 objects) and 394 non-cluster objects surrounding them show some differences. About 75% of the YSOs belonging to the IRAS clusters have an evolutionary age greater than yr. Their slope of the KLF agrees well with a Salpeter-type initial mass function (IMF) ( ) for a high mass range (O–F stars, ) at 1 Myr. The non-cluster objects are uniformly distributed in the molecular cloud, 80% of which are located to the right of the 0.1 Myr isochrone. The slope of the KLF of non-cluster objects is , corresponding better to a Salpeter-type IMF for low-mass objects (G–M stars, ). Our results show that two dense stellar clusters are embedded in these two physically connected UC HII regions. The clusters include several high- and intermediate-mass zero-age main sequence stellar objects. Based on the small age spread of the stellar objects, we suggest that the clusters originate from a single triggering shock. The extended emission observed in both UC HII regions is likely due to the stellar clusters.
The γ -ray spectrum of the source HAWC J1825-134 measured with the High Altitude Water Cherenkov (HAWC) observatory extends beyond 200 TeV without any evidence for a steepening or cutoff. There are some indications that the γ -rays detected with HAWC were produced by cosmic-ray protons or nuclei colliding with the ambient gas. Assuming primary protons, we inquire which shape of the primary proton spectrum is compatible with the HAWC measurements. We find that the primary proton spectrum with the power-law shape of γ p = 2.2 and the cutoff energy E c − p > 500 TeV describes the data well. However, much harder spectra with γ p down to 1.3 and E c − p as low as 200 TeV also do not contradict the HAWC measurements. The former option might be realized if the accelerator is inside or very near to the γ -ray production zone. The latter option is viable for the case of a cosmic-ray source that effectively confines low-energy ( E p < 10 TeV) accelerated protons. Using publicly available data of the Fermi-LAT space γ -ray telescope, we derive upper limits on the intensity of the HAWC J1825-134 source in the 1 GeV–1 TeV energy range. We show that the account of these upper limits drastically changes the interpretation: only hard ( γ p < 1.7) spectra describe the combined HAWC and Fermi-LAT data sets well.
Context. γ Cygni is a young supernova remnant located in the Cygnus region. MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes detected TeV emission (MAGIC J2019+408) to the north-west of this remnant, ~5’ from its border.
Aims. We want to identify the radio sources within the region encompassing γ Cygni and MAGIC J2019+408 to shed light on their nature and investigate if these radio sources could be potential contributors to gamma-ray emission.
Methods. We carried out a detailed study of the data we obtained with a survey of the Cygnus region at 325 and 610 MHz with the Giant Metrewave Radio Telescope.
Results. We detected several radio sources in the region where the radio and the TeV emission overlap, as well as several areas of enhanced radio emission. In particular, two of these areas of diffuse enhanced emission may correspond to the supernova remnant interacting with a high density region, which seems to be the best candidate for the MAGIC source. Another two radio sources, which may or may not contribute to the gamma rays, are also spatially coincident with the emission peak of the MAGIC TeV source. One of them displays a rather peculiar extended morphology whose nature is completely unknown.
Conclusions. We have identified the radio sources overlapping γ Cygni and MAGIC J2019+408 and have shown that their potential gamma-ray contribution is likely not dominant. In addition, some of the studied sources show peculiar physical characteristics that deserve deeper multi-wavelength observations.
The stellar content and physical properties of the molecular clouds associated with 21 bright far-IR sources in the outer Galaxy have been determined through C-12O, C-13O, 6-cm radio continuum, and IRAS observations. The molecular cloud masses range from 200 to about 10,000 solar masses. The far-IR luminosity-to-mass ratio for these clouds has a mean value of 6.8 solar luminosity/solar masses and shows no correlation with the cloud mass, a result similar to that found for more massive clouds in the inner Galaxy. The radio continuum survey of the 21 bright far-IR sources indicates that most of these regions probably have a single, massive star providing most of the ionization. The cloud masses derived from virial and LTE analyses are in agreement, supporting the assumptions commonly made in their calculations, and a tight, near-linear correlation is found between the C-12O luminosity and the cloud mass. The H2 column density and integrated C-12O intensity are also correlated on a point-by-point basis, although the scatter is larger than the C-12O luminosity-cloud mass relation. 61 refs.
Sources with (K)-(L) colors greater than 2 were found in a sample of 46
H2O masers using 3.6 micron photometric measurements. Many of these
sources have near infrared energy distributions similar to known
pre-main sequence objects; a number of infrared objects increases with
the H2O maser distance and the (K)-(L) color indicates that the infrared
and maser sources are related. Eleven of the infrared objects are
coincident with the H2O masers; however, a statistical analysis of the
observed angular separations shows that positional incidences may be
involved in a larger sample of 18 objects, and that a distribution of
the actual separations broader than a few arc-s is not likely.
Ninety-one sources that appeared to be point sources when observed with
the angular resolution of the 100-m telescope at 4.9 GHz, and that were
expected to be H II regions, were examined. Five sources were found to
be nonthermal, one source was a planetary nebula and the remaining 85
sources were H II regions. Distance estimates were obtained for 50 of
the 85 H II regions, and their physical parameters were determined.
Approximately 85% of 25 H II regions observed with the NRAO
interferometer appeared to contain one or more compact components, with
excitation parameters equal to or larger than that of an 09.5 star. Four
of the compact components have electron densities greater than 10,000/cu
cm, and thus, the sources belong to the class of the most compact H II
regions observed at radio frequencies so far.
This paper presents maps of the continuum emission from the H II regions
W3, NGC 1976, NGC 2024, Sgr B2, W43, W49 A, W51 A, K3-50/NGC 6857,
W75/DR21, and NGC 7538 at 3.5 mm and from M17 at 3.2 mm observed with
the 12 m millimeter-wave telescope of NRAO. Comparison of these maps
with similar maps at centimeter wavelengths shows the 3.5 mm emission to
be primarily bremsstrahlung.
VLA observations of the ON1 region in the (J, K) = (1, 1) line of NH3
and the H76-alpha recombination line are reported. Dense and cool NH3
condensations with size scales of 0.2-0.3 pc are found near the
ultracompact H II region, ON1. From the systematic shift in position
with velocity, some of the condensations are interpreted as parts of a
rapidly rotating structure with a large velocity gradient of 11 + or - 2
km/s/pc. This rapid rotation may be the 'spin-up' motion expected from
partial conservation of the angular momentum during the collapse
process. This type of rapid rotation at the 0.1 pc scale may be a key in
identifying a collapsing region. The H76-alpha recombination line has a
peak velocity of 5.1 + or - 2.5 km/s and is blueshifted with respect to
both the NH3 emission and the OH maser emission. From the morphology, it
is likely that the H II region has a peculiar velocity with respect to
the neutral molecular material, while the OH masers may still be falling
in toward the exciting star.
The authors present measurements of the velocity line width, size,
virial mass, and CO luminosity for 273 molecular clouds in the Galactic
disk between longitudes of 8° and 90°. These are obtained from
three-dimensional data in the Massachusetts-Stony Brook CO Galactic
Plane Survey. It is shown that the molecular clouds are in or near
virial equilibrium and are not confined by pressure equilibrium with a
warm or hot phase of interstellar matter. The velocity line width is
proportional to the 0.5 power of the size, σv ∝
S0.5. A tight relationship, over four orders of magnitude, is
found between the cloud dynamical mass, as measured by the virial
theorem, and the CO luminosity M ∝ (LCO)0.81.
The cloud CO luminosity is LCO∝
σv5.
By using the Haystack 37 m antenna, a discovery was made of maser
emission in the 7(-2)-8(-1)E, 6(2)-5(3)A(-), and 6(2)-5(3)A(+)
transitions of interstellar methanol. All three lines were detected
toward the compact H II regions W3(OH) and NGC 6334-F. Toward the latter
source intensities in excess of 100 Jy are observed in all three
transitions. Masers in the 7(-2)-8(-1)E line were detected in three
additional sources. All sources toward which maser action was found are
associated with compact H II regions and are known to show strong maser
emission in the 12.2 GHz 2(0)-3(-1)E line of methanol at similar
velocities. For this reason the newly detected masers are classified as
class B methanol masers. Toward Orion-KL, thermal emission is observed.
The 2.5 m antenna of the Observatoire de Bordeaux is used to map the
molecular gas complex associated with the Sharpless 247/252 H II regions
in the J = 1-0 transition of C(O-13). The data show the existence of a
bridge between the S 247 S 252 molecular clouds as well of a complex
kinematic structure. A search for OH masers at 18 cm was carried out in
the vicinity of the ionization front of the S 247 H II region and two OH
masers were found.
Results are presented from multifrequency-VLA continuum and
spectral-line observations for three compact H II regions: G31.28 +
0.06, G33.92 + 0.11, and G34.25 + 0.14. It is found that the continuum
images of G31.28 + 0.06 at 20 and 3.6 cm show a cometary morphology,
although the combination of resolution and sensitivity of the 6-cm image
shows that this region is actually a shell source where the continuum
emission from one part of the shell dominates the emission from the rest
of the shell. The high-resolution 20-cm continuum emission from G33.92 +
0.11 also shows a shell source whose continuum emission is dominated by
one side of the shell. The image of 34.25 + 0.14 shows a ring of
emission of a diameter equal to about 1 arcmin. This structure appears
to be a shell which is 75 percent complete.
The compact H II region W3 (OH) has been mapped at 31.4 GHz with
0.3-arcsec resolution. The emission is concentrated in an irregular ring
with a low central minimum, and an electron density in the shell of at
least 200,000/cu cm is implied. One group of OH maser sources lies near
a continuum peak, another is south of the source, and the remainder are
on the periphery of the ionized gas. No emission is detected in the
vicinity of the H2O masers.
The broad-band energy distributions of BN-type objects is investigated.
The IRAS color indices are within R(12/25) values between 0.0 and 1.0,
R(25/60) values between 0.0 and 0.6, and R(60/100) values between -0.2
and 0.2 and separate the BN-type objects from compact H II regions and
other IR sources. Also in the NIR two-color diagrams, this separation is
very clear. A relation between tan - Si and (K - L) is found which
resembles the interstellar extinction law. An averaged broad-band energy
distribution from 1 micron to 1300 microns for BN-type objects is given.
Bolometric luminosities of individual sources were calculated and appear
to be by about 30 percent higher than IRAS luminosities. Spectral
indices for the radio continuum emission were determined and used to
constrain the physical nature of the ionized regions.
Observations of the CO J = 1-0 and CS J = 2-1, 1-0 lines and 1.1 mm
continuum emissions around an infrared reflection nebula GGD 27 IRS are
presented. These observations revealed that this source is a
prototypical molecular bipolar flow which shows shell structure and
which is associated with a dense disk. The CO bipolar flow spatially
coincides with the infrared reflection nebula, suggesting that the
near-infrared light is scattered by the dust whose distribution is
conducted by the flow. A spatial coincidence of the expected cavity of
the molecular flow with the ionized gas is also noticed, which supports
a stellar wind-driven model of the outflow. The density and the mass of
the disk are deduced to be 1 x 10 to the 5th/cu cm and 120 solar masses,
respectively, from an LVG model calculated for the two transitions of
the CS molecule, and greater than 1.2 x 10 to the 5th/cu cm and 400
solar masses from the optical thickness of the cold dust at 1.1 mm.
Dust/gas envelope stars (DGE-stars), thought to be situated at the top
of the Asymptotic Giant Branch, are studied using IRAS two-color
diagrams. Consideration is given to the hypothesis that IRAS two-color
diagrams, together with data from the LRS catalog and information on the
IR variability, make it possible to distinguish stars with oxygen-rich
circumstellar shells from carbon-rich ones and to order stars according
to their mass loss rate. It has been suggested that carbon-rich material
is dredged up during a thermal pulse and this can cause the
trransformation of an oxygen-rich circumstellar shell into a carbon-rich
one.
Spectroscopic observations in the Br-alpha, Br-gamma, and Pf-gamma
hydrogen-recombination lines of 11 compact objects near H2O masers,
obtained during 1981 and 1982 using an InSb detector equipped with
continuously variable filters on the 3.6-m telescope at ESO, are
reported and analyzed. The derived correction factors are explained, and
the continuum and recombination-line data are presented in tables and
graphs and interpreted for each object. The objects G309.9+0.5,
G328.3+0.43, G351.41+0.64, and G5.9-0.4 are found to be ultracompact H
II regions (r at 10 microns less than or equal to 8 x 10 to the 16th
cm), whereas G324.2+00.12 is a compact H II region, and the nature of
the other objects remains unclear. A log-log plot IR luminosity versus
(ne squared) (V) for a 25-object sample drawn from these data
and from published data on other compact objects near H20 masers
suggests that all of them are OB stars with incompletely developed
ionization-bounded H II regions. A rough proportionality between H2O and
integrated IR fluxes is demonstrated, and the evolutionary relationships
implied are discussed.
Observations of the compact H II region W3 (OH), one of the youngest H
II regions in the Galaxy, made with the VLA at 2 and 1.3 cm with an
angular resolution of approximately 0.2 arcsec are reported. Maps
obtained reveal the ultracompact H II region to be a dense shell which
only starts to become optically thin at 1.3 cm, with outer diameter 5.9
x 10 to the 16th cm, thickness approximately 0.9 x 10 to the 16th cm,
mean electron density approximately 220,000/cu cm and electron
temperature approximately 9400 K. Accurate positions are also obtained
for the nearby water vapor masers, which were determined to have
continuum upper limits of 4.2 and 10.5 mJy at 2 and 1.3 cm,
respectively. The far infrared and radio luminosities indicate that the
H II region is excited by a main sequence O7 star, and is surrounded by
a cold dust cloud of central UV optical depth of 100, radius 1.7 x 10 to
the 18th cm and mass 100 solar masses. The shell is interpreted as the
ionized inner edge of a dust-enriched cocoon which formed around the
star in its protostellar stage. An upper limit of 270 years is derived
for the age of the H II region.
A total of 2298 IR H II regions in the IRAS Point Source Catalog are
identified to a confidence level of 77 percent. A latitude-longitude
plot shows that most of these regions lie in the region + or - 3 degrees
of the galactic plane. A set of 949 IRAS sources are shown to be
planetary nebulae to a 79 percent confidence level. These sources are
found within 10 degrees of the plane. Seven of the objects studied are
observed with VLA as a test of the analysis.
The continuum and recombination line data presented confirm the sense of
the radial velocity change reported by Berulis and Ershov (1983). The
radial velocity becomes about 5 km/sec more positive between 2-cm and
2-mm wavelengths; this is consistent with a combination of expansion,
optical depth, and non-LTE effects. Al alternative explanation involves
'champagne flow' off dense neutral regions, in conjunction with
different optical depths in the ionized gas. The data available do not
permit a definitive choice between the two models.
The H76α radio recombination line from two ultracompact H II
regions, G34.3+0.2 and G45.07+0.13, is mapped with an angular resolution
of 0arcsec.4 using the VLA. The line center velocity of G34.3+0.2 shows
a remarkably gradual shift across the source by ≡23 km
s-1. The radio continuum appearance of G34.3+0.2 might be
explained as the H II region being embedded in a dense molecular slab
and experiencing the "champagne" phase of its evolution. Further, the
velocity structure of G34.3+0.2 suggests that the circumstellar
molecular slab or disk is rotating around a central object, probably a
cluster of stars. The velocity and radio continuum structure of
G45.07+0.13 suggest the existence of an ionized ring that is expanding
at a velocity of 10 km s-1 with respect to the central star.
We observed with the VLA several regions of mass outflow at 20,6 and 2 cm:
LkHα 198, GL 490, HH 7-11, TTau, HLTau, GGD 12-15, GL961, GGD27-28,
V645Cyg, CepA, and MWC1080. In most of the regions no continuum source was
detected, down to the mJy level, at 6 cm that could be identified as the
energy source of the outflow. This result suggests that in these cases the
stellar winds powering the outflows are either neutral or, if ionized, have a
large terminal velocity (˜ 10^2 km s-1) T Tauri and most of the other
sources detected show spectra characteristic of an optically-thin H II region
and not that of simple ionized winds. We measured the positions of
several H2 0 masers associated with mass outflow regions: GL 490,
OMC(2)2, OMC(2)1, Mon R2, GGD 12-15, S106, GL 2591, NGC 7129(2), 5140
and Cep A.
A 10-GHz radio continuum survey of the galactic plane in the range
355° ≤ l ≤ 56°, -1°.5 ≤ b ≤ +1°.5 was made
at the Nobeyama Radio Observatory using the 45-m telescope. The
half-power beam size of the resultant map is 3arcmin.0 and the noise
level of the resultant map is typically 15 mK in brightness temperature.
Thirty-one contour maps and a list of 144 small-diameter sources are
presented.
Three ultracompact H II regions associated with OH masers are studied
with the VLA. Multiple structures are found in each region and are
interpreted as clusters of OB stars. This interpretation is supported in
the case of G10.6-0.4 by a good agreement between the distribution of
spectral types and the initial mass function of field stars. If the OB
cluser extends to lower mass stars, we find important implications about
the far-infrared characteristics of these regions and, in particular,
about the deduced properties of the dust in the H II regions. Size
scales and spatial distribution of the OB stars suggest that collision
processes between cloud fragments must have been important in the
evolution toward stars. The abundance of continuum structures also
suggests that the relation between OH masers and compact H II regions
may not be simple.
We present multifrequency, matching-beam VLA continuum observations of
the HH 80-81 system as well as high-resolution observations of its
central exciting source. A highly collimated bipolar jet emanates from
this central source along a line between the source and HH 80-81. The
jet consists of a multitude of knots, with a spacing of about 1400 AU
and widths of less than 500 AU. This is strikingly similar to the
structure of HH jets emanating from young stars more than a thousand
times less luminous. The southern lobe terminates in the visible HH
objects HH 80-81 at a projected distance of 2.3 pc from the central
source. These objects are detected and resolved at 6 cm and 3.6 cm with
a spectral index of α = -0.3. We find another resolved object 3.0
pc to the north of the source along the well-defined flow axis and with
the same negative spectral index, but without any known optical
counterpart. We here call this object HH 80 North. The total projected
dimension of 5.3 pc for this highly collimated outflow complex far
exceeds all other known HH complexes and is more than an order of
magnitude larger than the typical dimensions of such flows. There is
clear evidence for a gentle wiggling of the flow axis, suggesting that
the driving source may be precessing. The remarkable structural
similarity between the HH 80-81 jet and HH jets from low luminosity
stars suggests that massive newborn stars pass through very similar
evolutionary phases.
The galactic H II region K3-50 has been mapped in Bralpha infrared and 110alpha radio recombination lines with a resolution of about 5arcsec. Pressure broadening is found to be important in the compact components. The observed broad H110alpha lines imply true electron densities >105cm-3. Narrow line H110alpha(H I) emission from the partially ionized medium is observed towards K3-50 A (FWHM ≡ 4 km s-1) and Cl (ON3, FWHM ≡ 14 km s-1). The visual extinction Alphav due to foreground material has been determined by comparing the radio continuum and Bralpha intensity. An extinction of Alphav >= 190 mag is found towards the core of component Cl. In the direction of component Cl the Bralpha, 4 mum continuum and radio data suggest the presence of a disk of molecular material observed edge-on.
Observations of 13CO and 12CO have been made in the direction of 96 infrared sources selected from the IRAS point-source catalogue, and having a flux density at 100 mum greater than at 60 mum, so that their color temperature T(60/100) is lower than 50K. Among these objects, 83 have been detected in 13CO and 37 have been mapped. About half of the associated molecular clouds have a "globule-like" morphology. The other half corresponds to extensions of molecular clouds associated to H II regions. The authors have observed 24 sources in 12CO; 50% are good candidates for having molecular flows. For two of them the presence of outflows has been confirmed. Therefore these cold IRAS sources are very likely to be pre-main-sequence stars still embedded in their parent molecular cloud. The authors also derive a relationship between the total infrared luminosity and the total H2 mass in a 4arcmin.4 beam centered on the IR source: Lir is proportional to M(H2)1.4.
A detailed discussion of 22 H II regions with small structure in their
radio emission is presented. These regions represent the most
interesting objects of a λ=6 cm survey of 74 H II regions made
with the Westerbork Synthesis Radio Telescope (Felli et al, 1978).
Of the 22 objects discussed, 12 can be classified as compact H II
regions with an internal source of excitation. The remaining small
diameter radio features are found in more extended H II regions and can
be attributed to increases in the electron density at ionization fronts
located at the edges of dense molecular clouds. Their ionization can be
accounted for by the same early type star which ionizes the diffuse
extended H II region in which they are located.
The compact components found in this survey, are usually associated with
small bright optical nebulosities, but seldom with diffuse extended low
density H II regions. These results imply that, in our sample, the
expansion of an H II region plays little role as the trigger of the next
generation star formation. Several nebulae in our sample have
blister-like configurations and/or bipolar nebulae, in which the ionized
gas is flowing away in the two opposite directions perpendicular to a
flat, disk-like, molecular cloud. Under assumption that the radio
continuum emission of the ionized gas, the infrared emission of the
heated dust and the molecular emission are all energized by a single
stellar source, the spectral type of the required star is derived
independently from the measured flux densities measured in the three
wavelength regions for a limited number of nebulae for which sufficient
information is available. The values obtained are in good agreement,
suggesting that a hidden early-type star can be the main source of
energy supply for the radio, infra-red and molecular emission in compact
H II region, IR source, molecular hot spot complexes.
We have observed the (4,4) and (5,5) inversion transitions of ammonia
towards 16 ultracompact H II regions known to be strong NH3(2,2)
emitters. 15 of these were detected in the (4,4) line and 10 were also
observed and detected in the (5,5) transition. Our results indicate that
emission from hot molecular gas is the rule rather than the exception in
such regions. Combining our observations with earlier measurements of
the (1,1) and (2,2) lines, we find that the inferred level populations
can be fit with a single rotational temperature: only G10.47+0.03A and
G31.41+0.31 are clearly inconsistent with a single component model.
Towards these latter two sources, we detect the hyperfine satellites of
the (4,4) and (5,5) transitions and derive line optical depths greater
than 100. This suggests the presence of very compact high density
regions with ammonia column densities as high as 10 exp 19/sq cm and
temperatures of order 200 K. We also report the detection of the first
maser in a metastable transition of para-ammonia (NH3(5,5)) toward
G9.62+0.19 and absorption in NH3(5,5) towards G45.47+0.05; the latter is
discussed in detail. Finally, serendipitous detections of the H92-gamma
recombination line are presented.