K. M. Menten’s research while affiliated with Max Planck Institute for Radio Astronomy and other places

We used ALMA to perform a line survey of the high-mass star forming region Sgr B2(N), called ReMoCA. We modeled under the assumption of LTE the spectra obtained toward the sources embedded in the secondary hot core Sgr B2(N2). We compared the chemical composition of these sources to that of sources from the literature and to predictions of the chemical kinetics model MAGICKAL. We detected up to 58 molecules toward Sgr B2(N2)'s hot cores, including up to 24 COMs, as well as many less abundant isotopologs. The compositions of some pairs of sources are well correlated, but differences also exist in particular for HNCO and NH2CHO. The abundances of series of homologous molecules drop by about one order of magnitude at each further step in complexity. The nondetection of radicals yields stringent constraints on the models. The comparison to the chemical models confirms previous evidence of a high cosmic-ray ionization rate in Sgr B2(N). The comparison to sources from the literature gives new insight into chemical differentiation. The composition of most hot cores of Sgr B2(N2) is tightly correlated to that of the hot core G31.41+0.31 and the hot corino IRAS 16293-2422B after normalizing the abundances by classes of molecules (O-, N-, O+N-, and S-bearing). There is no overall correlation between Sgr B2(N2) and the shocked region G+0.693-0.027 also located in Sgr B2, and even less with the cold starless core TMC-1. The class of N-bearing species reveals the largest variance among the four classes of molecules. The S-bearing class shows in contrast the smallest variance. These results imply that the class of N-bearing molecules reacts more sensitively to shocks, low-temperature gas phase chemistry after non-thermal desorption, or density. The abundance shifts observed between the N- and O-bearing molecules may indicate how violently and completely the ice mantles are desorbed. [abridged]

The Galactic edge, at Galactocentric distances of 14,--,22,kpc, provides an ideal laboratory for studying molecular clouds in an environment that is different from the solar neighborhood, due to its lower gas density, lower metallicity, and little or no perturbation from the spiral arms. Observations of CO,(J,=,2--1) spectral lines were carried out toward 72 molecular clouds located at the Galactic edge using the IRAM,30,m telescope. With these observations combined with CO,(J,=,1--0) data from the MWISP project, we investigated the variations in R_21 across these Galactic edge clouds, with R_21 representing CO(2-1)/CO(1-0) integrated intensity ratios. They are found to range from 0.3 to 3.0 with a mean of 1.0,±,0.1 in the Galactic edge clouds. The proportions of very low-ratio gas (R_21,<,0.4), low-ratio gas (0.4,le,R_21,<,0.7), high-ratio gas (HRG; 0.7,le,R_21,<,1.0), and very high-ratio gas (VHRG; R_21,ge,1.0) are 6.9%, 29.2%, 26.4%, and 37.5%, respectively, indicating a significant presence of high R_21 ratio molecular gas within these regions. In our Galaxy, the gradient of the R_21 ratio exhibits an initial radial decline followed by a high dispersion with increasing Galactocentric distance and a prevalence for VHRG. There is no apparent systematic variation within the Galactocentric distance range of 14 to 22,kpc. A substantial proportion of HRG and VHRG is found to be associated with compact clouds and regions of star-forming activity, suggesting that the high R_21 ratios stem from dense gas concentrations and recent episodes of star formation.

The Galactic edge at Galactocentric distances of 14\,--\,22\,kpc provides an ideal laboratory to study molecular clouds in an environment that is different from the solar neighborhood, due to its lower gas density, lower metallicity, and little or no perturbation from the spiral arms. Observations of CO\,(J\,=\,2--1) spectral lines were carried out towards 72 molecular clouds located at the Galactic edge using the IRAM\,30\,m telescope. Combined with CO\,(J\,=\,1--0) data from the MWISP project, we investigate the variations of $R_{21}$ across these Galactic edge clouds, with $R_{21}$ representing CO(2-1)/CO(1-0) integrated intensity ratios. These are found to range from 0.3 to 3.0 with a mean of 1.0\,$\pm$\,0.1 in the Galactic edge clouds. The proportions of very low ratio gas (VLRG; $R_{21}$\,<\,0.4), low ratio gas (LRG; 0.4\,$\le$\,$R_{21}$\,<\,0.7), high ratio gas (HRG; 0.7\,$\le$\,$R_{21}$\,<\,1.0), and very high ratio gas (VHRG; $R_{21}$\,$\ge$\,1.0) are 6.9\%, 29.2\%, 26.4\%, and 37.5\%, respectively, indicating a significant presence of high $R_{21}$ ratio molecular gas within these regions. In our Galaxy, the $R_{21}$ ratio exhibits a gradient of initial radial decline followed by a high dispersion with increasing Galacticentric distance and a prevalence for high ratio gas. There is no apparent systematic variation within the Galactocentric distance range of 14 to 22\,kpc. A substantial proportion of HRG and VHRG is found to be associated with compact clouds and regions displaying star-forming activity, suggesting that the high $R_{21}$ ratios may stem from dense gas concentrations and recent episodes of star formation.

Massive star formation is associated with energetic processes that may influence the physics and chemistry of parental molecular clouds and impact galaxy evolution. The high-mass protostar DR21 Main in Cygnus X possesses one of the largest and most luminous outflows ever detected in the Galaxy, but the origin of its structure and driving mechanisms are still debated. Our aim is to spatially resolve the far-infrared line emission from DR21 Main and to investigate the gas physical conditions, energetics, and current mass loss rates along its outflow. Far-infrared SOFIA FIFI-LS spectra covering selected high-J CO lines, OH O i C ii and O iii lines are analyzed across almost the full extent of the DR21 Main outflow using 2.00arcmin times 3.75arcmin mosaic. The spatial extent of far-infrared emission closely follows the well-known outflow direction of DR21 Main in the case of high-J CO O i 63.18 μm, and the OH line at 163.13 μm. On the contrary, the emission from the C ii 157.74 μm and O i 145.53 μm lines arises mostly from the eastern part of the outflow, and is likely linked with a photodissociation region. Comparison of non-LTE radiative transfer models with the observed O I line ratios suggest H_2 densities of ∼10^5 cm^-3 in the western part of the outflow and ∼10^4 cm^-3 in the east. Such densities are consistent with the predictions of UV-irradiated non-dissociative shock models for the observed ratios of CO and O i along the DR21 Main outflow. Assuming that the bulk of the emission arises in shocks, the outflow power of DR21 Main of $4.3-4.8 L_⊙ and the mass loss rate of$3.3-3.7 M_⊙ yr^-1 are determined, consistent with estimates using HCO^+ 1-0. Spatially resolved far-infrared emission of DR21 Main provides a strong support for its origin in outflow shocks, and the stratification of physical conditions along the outflow. The total line cooling provides additional evidence that DR21 Main drives one of the most energetic outflows in the Milky Way.

Low- and intermediate-mass stars on the asymptotic giant branch (AGB) account for a significant portion of the dust and chemical enrichment in their host galaxy. Here we present ALMA observations of the continuum emission at 1.24 mm around a sample of 17 stars from the ATOMIUM survey. From our analysis of the stellar contributions to the continuum flux, we find that the semi-regular variables all have smaller physical radii and fainter monochromatic luminosities than the Mira variables. Comparing these properties with pulsation periods, we find a positive trend between stellar radius and period only for the Mira variables with periods above 300 days and a positive trend between the period and the monochromatic luminosity only for the red supergiants and the most extreme AGB stars with periods above 500 days. We find that the continuum emission at 1.24 mm can be classified into four groups. "Featureless" continuum emission is confined to the (unresolved) regions close to the star for five stars in our sample, relatively uniform extended flux is seen for four stars, tentative bipolar features are seen for three stars, and the remaining five stars have unique or unusual morphological features in their continuum maps. These features can be explained by binary companions to 10 out of the 14 AGB stars in our sample. Based on our results we conclude that there are two modes of dust formation: well established pulsation-enhanced dust formation and our newly proposed companion-enhanced dust formation. If the companion is located close to the AGB star, in the wind acceleration region, then additional dust formed in the wake of the companion can increase the mass lost through the dust driven wind. This explains the different dust morphologies seen around our stars and partly accounts for a large scatter in literature mass-loss rates, especially among semiregular stars with small pulsation periods.

We present high-frequency (18–24 GHz) radio continuum observations towards 335 methanol masers, excellent signposts for young, embedded high-mass protostars. These complete the search for hypercompact H ii (HC H ii) regions towards young high-mass star-forming clumps within the fourth quadrant of the Galactic plane. HC H ii regions are the earliest observable signatures of radio continuum emission from high-mass stars ionizing their surroundings, though their rarity and short lifetimes make them challenging to study. We have observed methanol maser sites at 20-arcsec resolution and identified 121 discrete high-frequency radio sources. Of these, 42 compact sources are embedded in dense clumps and coincide with methanol masers, making them as excellent HC H ii region candidates. These sources were followed up at higher resolution (0.5-arcsec) for confirmation. We constructed spectral energy distributions across 5–24 GHz to determine their physical properties, fitting either a simple H ii region model or a power-law as needed. This analysis identified 20 HC H ii regions, 9 intermediate objects, 3 UC H ii regions, and 3 radio jet candidates. Combining these results with previous findings, the SCOTCH survey has identified 33 HC H ii regions, 15 intermediate objects, 9 UC H ii regions, and 4 radio jet candidates, tripling the known number of HC H ii regions. Eleven of these sources remain optically thick at 24 GHz. This survey provides a valuable sample of the youngest H ii regions and insights into early massive star formation.

Massive star formation is associated with energetic processes that may influence the physics and chemistry of parental molecular clouds and impact galaxy evolution. The high-mass protostar DR21 Main in Cygnus X possesses one of the largest and most luminous outflows ever detected in the Galaxy, but the origin of its structure and driving mechanisms is still debated. Our aim is to spatially resolve the far-infrared line emission from DR21 Main and to investigate the gas physical conditions, energetics, and current mass loss rates along its outflow. Far-infrared SOFIA FIFI-LS spectra covering selected high-J CO lines, OH, [O I], [CII] and [O III] lines are analyzed across the almost full extent of the DR21 Main outflow using 2.00' x 3.75' mosaic. The spatial extent of far-infrared emission follows closely the well-known outflow direction of DR21 Main in case of high-J CO, [O I] 63.18 um, and the OH line at 163.13 um. On the contrary, the emission from the [C II] 157.74 um and [O I] 145.53 um lines arises mostly from the eastern part of the outflow, and it is likely linked with a photodissociation region. Comparison of non-LTE radiative transfer models with the observed [O I] line ratios suggest H2 densities of ~10^5 cm^(-3) in the western part of the outflow and ~10^4 cm^(-3) in the East. Such densities are consistent with the predictions of UV-irradiated non-dissociative shock models for the observed ratios of CO and [O I] along the DR21 Main. Main outflow. Assuming that the bulk of emission arises in shocks, the outflow power of DR21 Main of 4.3-4.8x10^2 Lsol and the mass-loss rate of 3.3-3.7x10^(-3) Msol/yr are determined. Observations provide strong support for its origin in outflow shocks, and the stratification of physical conditions along the outflow. The total line cooling provides additional evidence that DR21 Main drives one of the most energetic outflows in the Milky Way.

Context . Strong laser emission from hydrogen cyanide (HCN) at 805 and 891 GHz has been discovered towards carbon-rich (C-rich) asymptotic giant branch (AGB) stars. Both lines belong to the Coriolis-coupled system between the (1,1 1e ,0) and (0,4 ⁰ ,0) vibrational states, which has been extensively studied in early molecular spectroscopy in the laboratory. However, the other lines in this system with frequencies above ∼900 GHz, which are challenging to observe with ground-based telescopes, have remained unexplored in astronomical contexts. Aims . We aim to (1) search for new HCN transitions that show laser activity in the (0,4 ⁰ ,0), J = 10−9 line at 894 GHz, the (1,1 1e ,0)−(0,4 ⁰ ,0), J = 11−10 line at 964 GHz, the (1,1 1e ,0), J = 11−10 at 968 GHz, and the (1,1 1e ,0), J = 12−11 line at 1055 GHz towards C-rich AGB stars; (2) study the variability of multiple HCN laser lines, including the two known lasers at 805 and 891 GHz; and (3) construct a complete excitation scenario to the Coriolis-coupled system. Methods . We conducted SOFIA/4GREAT observations and combined our data with Herschel /HIFI archival data to construct a sample of eight C-rich AGB stars, covering six HCN transitions (i.e. the 805, 891, 894, 964, 968, and 1055 GHz lines) in the Coriolis-coupled system. Results . We report the discovery of HCN lasers at 964, 968, and 1055 GHz towards C-rich AGB stars. Laser emission in the 805, 891, and 964 GHz HCN lines was detected in seven C-rich stars, while the 968 GHz laser was detected in six stars and the 1055 GHz laser in five stars. Notably, the 894 GHz line emission was not detected in any of the targets. Among the detected lasers, the emission of the cross-ladder line at 891 GHz is always the strongest, with typical luminosities of a few 10 ⁴⁴ photons s ⁻¹ . The cross vibrational state 964 GHz laser emission, which is like a twin of the 891 GHz line, is the second strongest. The 1055 GHz laser emission always has a stronger 968 GHz counterpart. Towards IRC+10216, all five HCN laser transitions were observed in six to eight epochs and exhibited significant variations in line profiles and intensities. The 891 and 964 GHz lines exhibit similar variations, and their intensity changes do not follow the near-infrared light curve (i.e. they have non-periodic variations). In contrast, the variations in the 805, 968, and 1055 GHz lines appear to be quasi-periodic, with a phase lag of 0.1–0.2 relative to the near-infrared light curve. A comparative analysis indicates that these HCN lasers may be seen as analogues to vibrationally excited SiO and H 2 O masers in oxygen-rich stars. Conclusions . We suggest that chemical pumping and radiative pumping could play an important role in the production of the cross-ladder HCN lasers, while the quasi-periodic behaviour of the rotational HCN laser lines may be modulated by additional collisional and radiative pumping driven by periodic shocks and variations in infrared luminosity.

Context. Understanding the chemistry of molecular clouds is pivotal to elucidate star formation and galaxy evolution. As one of the important molecular ions, HCNH ⁺ plays an important role in this chemistry. Yet, its behavior and significance under extreme conditions, such as in the central molecular zones (CMZs) of external galaxies, are still largely unexplored. Aims. We aim to reveal the physical and chemical properties of the CMZ in the starburst galaxy NGC 253 with multiple HCNH ⁺ transitions to shed light on the molecule’s behavior under the extreme physical conditions of a starburst. Methods. We employed molecular line data including results for four rotational transitions of HCNH ⁺ from the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) large program to investigate underlying physical and chemical processes. Results. Despite weak intensities, HCNH ⁺ emission is widespread throughout NGC 253’s CMZ, which suggests that this molecular ion can effectively trace large-scale structures within molecular clouds. Using the quantum mechanical coupled states’ approximation, we computed rate coefficients for collisions of HCNH ⁺ with para -H 2 and ortho -H 2 at kinetic temperatures up to 500 K. Using these coefficients in a non-local-thermodynamic-equilibrium (non-LTE) modeling framework and employing a Monte Carlo Markov chain analysis, we find that HCNH ⁺ emission originates from regions with H 2 number densities of ∼ 10 2.80 −10 3.55 cm ⁻³ , establishing HCNH ⁺ as a tracer of low-density environments. Our analysis reveals that most of the HCNH ⁺ abundances in the CMZ of NGC 253 are higher than all values reported in the Milky Way. We perform static, photodissociation region, and shock modeling, and found that recurrent shocks could potentially account for the elevated HCNH ⁺ abundances observed in this CMZ. Conclusions. We propose that the unexpectedly high HCNH ⁺ abundances may result from chemical enhancement, primarily driven by the elevated gas temperatures and cosmic ray ionization rates of shocked, low-density gas in the nuclear starburst regions of NGC 253.

Strong laser emission from hydrogen cyanide (HCN) at 805 and 891 GHz has been discovered towards carbon-rich (C-rich) AGB stars, originating from the Coriolis-coupled system between two (1,1^{1e},0) and (0,4^0,0) vibrational states. However, other lines (at 894, 964, 968 and 1055 GHz) in this system remained unexplored due to observational challenges. Using SOFIA/4GREAT observations and Herschel/HIFI archival data, we analyzed the six HCN transitions in eight C-rich AGB stars. We report new HCN transitions show laser action at 964, 968, and 1055 GHz. The 805, 891, and 964 GHz lasers were detected in seven C-rich stars, the 968 GHz laser in six, and the 1055 GHz laser in five, while the 894 GHz line was not detected in any target. Among the detected lasers, the 891 GHz laser is always the strongest, and the 964 GHz laser, like a twin of the 891 GHz line, is the second strongest. Towards IRC+10216, all five HCN laser transitions were observed in six to eight epochs and exhibited significant variations in line profiles and intensities. The cross-ladder lines at 891 and 964 GHz exhibit similar variations, and their intensity changes do not follow the near-infrared light curve (i.e. non-periodic variations). In contrast, the variations of the rotational lines at 805, 968, and 1055 GHz appear to be quasi-periodic, with a phase lag of 0.1 - 0.2 relative to the near-infrared light curve. A comparative analysis indicates that these HCN lasers may be seen as analogues to vibrationally excited SiO and water masers in oxygen-rich stars. We suggest chemical pumping and radiative pumping could play an important role in the production of the cross-ladder HCN lasers, while the quasi-periodic behavior of the rotational HCN laser lines may be modulated by additional collisional and radiative pumping driven by periodic shocks and variations in infrared luminosity. [abridged]