Publications (25)0 Total impact
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Article: Long term Arecibo monitoring of the water megamaser in MG J0414+0534
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ABSTRACT: We monitored the 22 GHz maser line in the lensed quasar MG J0414+0534 at z=2.64 with the 300-m Arecibo telescope for almost two years to detect possible additional maser components and to measure a potential velocity drift of the lines. The main maser line profile is complex and can be resolved into a number of broad features with line widths of 30-160 km/s. A new maser component was tentatively detected in October 2008 at a velocity of +470 km/s. After correcting for the estimated lens magnification, we find that the H2O isotropic luminosity of the maser in MG J0414+0534 is about 26,000 solar luminosities, making this source the most luminous ever discovered. Both the main line peak and continuum flux densities are surprisingly stable throughout the period of the observations. An upper limit on the velocity drift of the main peak of the line has been estimated from our observations and is of the order of 2 km/s per year. We discuss the results of the monitoring in terms of the possible nature of the maser emission, associated with an accretion disk or a radio jet. This is the first time that such a study is performed in a water maser source at high redshift, potentially allowing us to study the parsec-scale environment around a powerful radio source at cosmological distances.04/2012; -
Article: Narrow-line Seyfert 1 galaxies: an amasing class of AGN
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ABSTRACT: [Abridged] Narrow-line Seyfert 1 (NLS1) galaxies are a class of active galactic nuclei (AGN) that have all the properties of type 1 Seyfert galaxies but show peculiar characteristics, including the narrowest Balmer lines, strongest Fe II emission, and extreme properties in the X-rays. Line and continuum radio observations provide an optimal tool to access the (often) optically obscured innermost regions of AGN and reveal the kinematics of the gas around their central engines. We investigate the interplay between the peculiar NLS1 class of AGN and the maser phenomenon, to help us understand the nature of the maser emission in some NLS1s where water maser emission has been detected. We observed a sample of NLS1 galaxies with the Green Bank Telescope in a search for water maser emission at 22 GHz. We also reduced and analysed archival Green Bank Telescope and Very Large Array data and produced 22-GHz spectra for the five NLS1 galaxies with detected maser emission. In particular, we imaged the maser and nuclear radio continuum of NGC5506 at subarcsec scales with the Very Large Array. We discovered maser emission in two NLS1 galaxies: IGRJ16385-2057, and IRAS03450+0055. In addition to the three previously known maser detections in the NLS1s Mrk766, NGC4051, and NGC5506, this yields a water maser detection rate in NLS1 galaxies of ~7% (5/71). This value rises significantly to ~21% (5/24) when considering only NLS1 galaxies at recessional velocities less than 10000 km/s. For NGC4051 and NGC5506, we find that the water maser emission is located within 5 and 12 pc, respectively, of nuclear radio continuum knots, which are interpreted as core-jet structures.07/2011; -
Article: Water vapour at high redshift: Arecibo monitoring of the megamaser in MG J0414+0534
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ABSTRACT: The study of water masers at cosmological distances would allow us to investigate the parsec-scale environment around powerful radio sources, to probe the physical conditions of the molecular gas in the inner parsecs of quasars, and to estimate their nuclear engine masses in the early universe. To derive this information, the nature of the maser source, jet or disk-maser, needs to be assessed through a detailed investigation of the observational characteristics of the line emission. We monitored the maser line in the lensed quasar MGJ0414+0534 at z = 2.64 with the 300-m Arecibo telescope for ~15 months to detect possible additional maser components and to measure a potential velocity drift of the lines. In addition, we follow the maser and continuum emissions to reveal significant variations in their flux density and to determine correlation or time-lag, if any, between them. The main maser line profile is complex and can be resolved into a number of broad features with line widths of 30-160 km/s. A new maser component was tentatively detected in October 2008 that is redshifted by 470 km/s w.r.t the systemic velocity of the quasar. The line width of the main maser feature increased by a factor of two between the Effelsberg and EVLA observations reported by Impellizzeri et al. (2008) and the first epoch of the Arecibo monitoring campaign. After correcting for the lens magnification, we find that the total H2O isotropic luminosity of the maser in MGJ0414+0534 is now ~30,000 Lsun, making this source the most luminous ever discovered.[Abridged]03/2011; -
Article: New Global VLBI observations of the gravitational lensing system MG J0414+0534
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ABSTRACT: The gravitational lens system MG J0414+0534 is formed by an elliptical galaxy at redshift ~0.96 and a quasar at z~2.64. The system geometry is typical of lensing by an elliptical galaxy with the QSO close to and inside a fold caustic. It shows 4 images of the background source, and a partial Einstein ring is visible at optical wavelengths. It was observed with a global-VLBI array at 18 cm in June 2008. We present here the imaging results and a preliminary lens model constrained by these observations. Comment: submitted to the proceedings of 10th European-VLBI network Symposium. 6 pages, 1 figure11/2010; -
Article: A search for gravitationally lensed water masers in dusty quasars and star-forming galaxies
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ABSTRACT: Luminous extragalactic water masers are known to be associated with AGN and have provided accurate estimates for the mass of the central supermassive black hole and the size and structure of the accretion disk in nearby galaxies. To find water masers at much higher redshifts, we have begun a survey of known gravitationally lensed quasars and star-forming galaxies. In this paper, we present a search for 22 GHz (rest frame) water masers toward five dusty, gravitationally lensed quasars and star-forming galaxies at redshifts 2.3--2.9 with the Effelsberg telescope and the EVLA. Our observations do not find any new definite examples of high redshift water maser galaxies, suggesting that large reservoirs of dust and gas are not a sufficient condition for powerful water maser emission. However, we do find the tentative detection of a water maser system in the active galaxy IRAS 10214+4724 at redshift 2.285. Our survey has now doubled the number of lensed galaxies and quasars that have been searched for high redshift water masers. We present an analysis of the high redshift water maser luminosity function that is based on the results presented here and from the only cosmologically distant (z > 1) water maser galaxy found thus far, MG J0414+0534 at redshift 2.64. By comparing with the luminosity function locally and at moderate redshifts, we find that there must be some evolution in the luminosity function of water maser galaxies at high redshifts. By assuming a moderate evolution [(1 + z )^4] in the luminosity function, we find that blind surveys for water maser galaxies are only worthwhile with extremely high sensitivity like that of the planned Square Kilometre Array. However, instruments like the EVLA and MeerKAT will be capable of detecting water maser systems similar to the one found from MG J0414+0534 through targeted observations. Comment: 10 pages, 4 figures, 4 tables, accepted for publication in MNRAS09/2010; -
Article: New water masers in Seyfert and FIR bright galaxies. IV. Interferometric follow-ups
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ABSTRACT: Very luminous extragalactic water masers, the megamasers, are associated with active galactic nuclei (AGN) in galaxies characterized by accretion disks, radio jets, and nuclear outflows. Weaker masers, the kilomasers, seem to be mostly related to star formation activity, although the possibility exists that some of these sources may belong to the weak tail of the AGN maser distribution. It is of particular importance to accurately locate the water maser emission to reveal its origin and shed light onto extragalactic star forming activity or to elucidate the highly obscured central regions of galaxies. We performed interferometric observations of three galaxies, NGC3556, Arp299, and NGC4151, where water emission was found. Statistical tools have been used to study the relation between OH and water maser emission in galaxies. The maser in NGC3556 is associated with a compact radio continuum source that is most likely a supernova remnant or radio supernova. In Arp299, the luminous water maser has been decomposed in three main emitting regions associated with the nuclear regions of the two main galaxies of the system, NGC3690 and IC694, and the region of overlap. In NGC4151, only one of the two previously observed maser components has been tentatively detected. This feature, if real, is associated with the galaxy's central region. The only galaxy, so far, where luminous maser emission from two maser species, OH and H2O has been confidently detected is Arp299. Weaker masers from these two species do instead coexist in a number of objects. A larger number of objects searched for both maser species are, however, necessary to better assess these last two results. Comment: 19 pages, 11 figures, 5 tables. Accepted by Astronomy & Astrophysics08/2010; -
Article: X-ray vs. water maser emission in AGN
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ABSTRACT: Correlations between X-ray and water maser emission in AGN have been recently reported. However, the lack of systematic studies affects the confidence level of these results. In the following, we introduce a project aimed at studying all the water maser sources believed to be associated with AGN activity through X-ray data obtained with the XRT and BAT instruments on-board the Swift satellite. Preliminary results of this work indicate a promising rate of XRT detections allowing us to refine follow-up observing strategies focused on investigating the nuclei of individual galaxies and deriving, on statistical basis, the main characteristics of water maser hosts. In addition, a cross-correlation between our sample and the BAT 22-months all-sky survey provides an exceptionally high detection rate at hard X-ray energies when compared to other AGN-related catalogs. Comment: 4 pages, 1 figure, to appear in refereed Proceedings of "X-ray Astronomy 2009: Present Status, Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelini12/2009; -
Article: New H2O masers in Seyfert and FIR bright galaxies. III. The Southern Sample
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ABSTRACT: Recently, a relationship between the water maser detection rate and far infrared (FIR) flux densities has been established as a result of two 22 GHz maser surveys in a complete sample of galaxies (Dec>-30 degree) with 100 micron flux densities of > 50 Jy and > 30 Jy. This survey has been extended to the southern galaxies in order to discover new maser sources and to investigate the galaxies hosting the maser spots with particular emphasis on their nuclear regions. A sample of 12 galaxies with Dec<-30 degree and S(100 micron)>50 Jy was observed with the 70-m telescope of the Canberra Deep Space Communication Complex (CDSCC) at Tidbinbilla (Australia) in a search for water maser emission. The average 3 sigma noise level of the survey is 15 mJy for a 0.42 km/s channel, corresponding to a detection threshold of ~0.1 solar luminosities for the isotropic maser luminosity at a distance of 25 Mpc. Two new detections are reported: a kilomaser with an isotropic luminosity L_H2O ~5 solar luminosities in NGC3620 and a maser with about twice this luminosity in the merger system NGC3256. The detections have been followed-up through continuum and spectral line interferometric observations with the Australia Telescope Compact Array (ATCA). In NGC3256, a fraction (about a third) of the maser emission arises from two hot spots associated with star formation activity, which are offset from the galactic nuclei of the system. The remaining emission may arise from weaker centers of maser activity distributed over the central 50 arcsec. [abridged] Comment: 13 pages, 9 figures, accepted by Astronomy and Astrophysics04/2009; -
Article: Evidence of a pure starburst nature of the nuclear region of NGC 253
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ABSTRACT: We present high-resolution spectral line and continuum VLBI and VLA observations of the nuclear region of NGC 253 at 22 GHz. While the water vapor masers in this region were detected on arcsecond and milliarcsecond scales, we could not detect any compact continuum emission with a 5 sigma upper limit of ~ 1 mJy. The observations reveal that the water maser emission is not related to a possible low-luminosity active galactic nucleus but is almost certainly associated with star-formation activity. Not detecting any compact continuum source on milliarcsecond scales also questions the presence of a - previously assumed - active nucleus in NGC 253.03/2009; -
Article: A gravitationally lensed water maser in the early Universe
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ABSTRACT: Water masers are found in dense molecular clouds closely associated with supermassive black holes in the centres of active galaxies. Based upon the understanding of the local water maser luminosity function, it was expected that masers at intermediate and high redshifts would be extremely rare, but galaxies at redshifts z > 2 might be quite different from those found locally, not least because of more frequent mergers and interaction events. Using gravitational lensing as a tool to enable us to search higher redshifts than would otherwise be possible, we have embarked on a survey of lensed galaxies, looking for masers. Here we report the discovery of a water maser at redshift 2.64 in the dust- and gas-rich gravitationally lensed type 1 quasar MG J0414+0534, which, with an isotropic luminosity of 10,000 L_solar, is twice as luminous as the most powerful local water maser, and half that of the most distant maser previously known. Using the locally-determined luminosity function, the probability of finding a maser this luminous associated with any single active galaxy is 10^{-6}. The fact that we saw such a maser in the first galaxy we observed must mean that the volume densities and luminosities of masers are higher at redshift 2.64.02/2009; -
Article: New water masers in Seyfert and FIR bright galaxies. II
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ABSTRACT: Recently, a relationship between the water maser detection rate and far infrared (FIR) flux density has been found as a result of a 22 GHz maser survey in a sample comprised of northern galaxies with 100 micron flux density > 50 Jy and a declination >-30 degrees. The survey has been extended toward galaxies with lower FIR flux densities in order to confirm this correlation and to discover additional maser sources for relevant follow-up interferometric studies. A sample of 41 galaxies with 30 Jy < S(100 micron) < 50 Jy and Dec. > -30 degrees was observed with the 100-m telescope at Effelsberg in a search for the 22 GHz water vapor line. The average 3-sigma noise level of the survey is 40 mJy for a 1 km/s channel, corresponding to a detection threshold for the isotropic maser luminosity of about 0.5 solar luminosities at a distance of 25 Mpc. Two detections are reported: a megamaser with an isotropic luminosity of approximately 35 solar luminosities in the Seyfert/HII galaxy NGC613 and a kilomaser of approximately 1 solar luminosity in the merger system NGC520.[abridged]01/2008; -
Article: Dissecting the star-formation history of starburst galaxies: the case of NGC7673
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ABSTRACT: We have collected archival data on NGC7673 to constrain the star-formation history that produced the young star clusters and the field stellar population in this galaxy during the last 2 Gyr. We have considered the sample of 50 star clusters detected by HST/WFPC2 in the UV, V and I bands and estimated their age, intrinsic reddening, and mass via comparison of their colours with STARBURST99 models. We have found two prominent epochs of cluster formation occurred about 20 Myr and 2 Myr ago, with somewhat minor events between 3 Myr and 6 Myr ago. The star clusters are characterised by an intrinsic reddening E(B-V) < 0.4 mag and a mass lower than 2e+06 solar masses. Out of the 50 star clusters, we have selected 31 located within the boundaries of the IUE large slit that was employed to obtain the spectrum of NGC7673 between 1150 Ang. and 3350 Ang. For each cluster, we have built a synthetic spectrum corresponding to the age, mass and intrinsic reddening derived from the cluster colours, properly redshifted to NGC7673. The spectra have then been added together in a final, clusters integrated spectrum. This and the IUE and FUSE spectra of NGC7673 have allowed us to describe the star-formation history of the unresolved stars in the field as either exponentially decaying or multi-burst. In the first case, we have derived an e-folding time of 700 (900) Myr and an initial star-formation rate of 16 (13) solar masses per year when the Fitzpatrick's (Calzetti's) extinction law is used. In the case of a multi-burst star-formation history, the field population turns out to be composed by a young (< 40 Myr) component 3 (2) times brighter than the star clusters, and a component as old as 850 (450) Myr, about 200 (100) times more massive than the star clusters together. Comment: 17 pages, 10 figures, accepted by MNRAS12/2007; -
Article: The water megamaser in the merger system Arp299
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ABSTRACT: We present preliminary results of an interferometric study of the water megamaser in the merger system Arp299. This system is composed of two main sources: IC694 and NGC3690. There is clear evidence that most of the water maser emission is associated with the nucleus of the latter, confirming the presence of an optically obscured AGN as previously suggested by X-ray observations. Furthermore, emission arises from the inner regions of IC694, where an OH megamaser is also present. The velocity of the water maser line is blueshifted w.r.t. the optically determined systemic velocity and is consistent with that of the OH megamaser line. This finding might then indicate that both masers are associated with the same (expanding) structure and that, for the first time, strong 22 GHz water and 1.67 GHz OH maser emission has been found to coexist.11/2006; -
Article: The HI content of the recently discovered field dwarf galaxy APPLES1
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ABSTRACT: We present observations in a search for neutral hydrogen associated with the recently detected field dwarf galaxy APPLES1, performed with the Parkes radiotelescope. The observed radio spectrum shows no evident (> 3sigma rms) line emission indicating an upper limit for the HI content of the galaxy of ~ 10E6 solar masses and providing an upper value for the M(HI)/L(B) ratio equal to 2.4 solar masses/solar luminosities. The low value of the HI content suggested by the observations, together with the galaxy optical morphology, might indicate that APPLES1 is a dwarf spheroidal. This indication is in contrast with the evidence of recent star formation, which is typical for dwarf irregular galaxies. This may suggest that APPLES1 belongs to the class of mixed dwarf irregular/spheroidal transition-type galaxies. We also conclude that the relatively low neutral gas mass in APPLES1 can be explained by an extended and inefficient star formation process, without the need for a dramatic event such as enhanced star formation or a past encounter with a massive galaxy or galaxy group. Comment: 5 pages including 2 figures, accepted for publication in A&A Main Journal08/2005; -
Article: New H2O masers in Seyfert and FIR bright galaxies
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ABSTRACT: Extragalactic water vapor masers with 50, 1000, 1, and 230 solar (isotropic) luminosities were detected toward Mrk1066 (UGC2456), Mrk34, NGC3556 and Arp299, respectively. The interacting system Arp299 appears to show two maser hotspots separated by 20 arcsec. A statistical analysis of 53 extragalactic H2O sources indicates (1) that the correlation between IRAS Point Source and H2O luminosities, established for individual star forming regions in the galactic disk, also holds for AGN dominated megamaser galaxies, (2) that maser luminosities are not correlated with 60/100 micron color temperatures and (3) that only a small fraction of the luminous megamasers detectable with 100-m sized telescopes have so far been identified. The slope of the H2O luminosity function, -1.5, indicates that the number of detectable masers is almost independent of their luminosity. If the LF is not steepening at very high maser luminosities, H2O megamasers at significant redshifts should be detectable with present day state-of-the-art facilities. Comment: 16 pages, 10 postscript figures; style file: aa.cls. Accepted for publication in the Main Journal of Astronomy & Astrophysics03/2005; -
Article: New H2O masers in Seyfert and FIR bright galaxies. IV. Interferometric follow-ups
http://dx.doi.org/10.1051/0004-6361/201014714. -
Article: New H$_{\mathsf 2}$O masers in Seyfert and FIR bright galaxies
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ABSTRACT: Context. A relationship between the water maser detection rate and far infrared (FIR) flux densities was established as a result of two 22 GHz maser surveys in a complete sample of galaxies ($\rm{Dec>-30^{\circ}}$) with $\rm{100~ \mu m}$ flux densities of $>$50 Jy and $>$30 Jy.Aims. We attempted to discover new maser sources and investigate the galaxies hosting the maser spots by extending previous surveys to southern galaxies with particular emphasis on the study of their nuclear regions.Methods. A sample of 12 galaxies with $\rm{Dec<-30^{\circ}}$ and $S_{100 ~ \mu \rm m}>50 ~\rm Jy$ was observed with the 70-m telescope of the Canberra deep space communication complex (CDSCC) at Tidbinbilla (Australia) in a search for water maser emission. The average 3$\sigma$ noise level of the survey was 15 mJy for a $\rm{0.42 ~km\, s^{-1}}$ channel, corresponding to a detection threshold of ${\sim} 0.1~\hbox{$L_{\odot}$}$ for the isotropic maser luminosity at a distance of 25 Mpc.Results. Two new detections are reported: a kilomaser with an isotropic luminosity $L_{\rm{H_{2}O}}\sim5~ \hbox{$L_{\odot}$}$ in NGC 3620 and a maser with about twice this luminosity in the merger system NGC 3256. The detections have been followed-up by continuum and spectral line interferometric observations with the Australia Telescope Compact Array (ATCA). In NGC 3256, a fraction (about a third) of the maser emission originates in two hot spots associated with star formation activity, which are offset from the galactic nuclei of the system. The remaining emission may originate in weaker centres of maser activity distributed over the central $50''$. For NGC 3620, the water maser is coincident with the nuclear region of the galaxy. Our continuum observations indicate that the nature of the nuclear emission is probably linked to particularly intense star formation. Including the historical detection in NGC 4945, the water maser detection rate in the southern sample is 15% (3/20), consistent with the northern sample. The high rate of maser detections in the complete all-sky FIR sample (23%, 15/65) confirms the existence of a link between overall FIR flux density and maser phenomena. A relation between H$_2$O and OH masers in the FIR sample is also discussed.http://dx.doi.org/10.1051/0004-6361/200911685. -
Article: New H$_{\mathsf 2}$O masers in Seyfert and FIR bright galaxies II. The intermediate luminosity range
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ABSTRACT: Context.Recently, a relationship between the water maser detection rate and far infrared (FIR) flux density has been found as a result of a 22 GHz maser survey in a sample comprised of northern galaxies with 100 $\mu$m flux density $>$50 Jy and a declination $>$-30°.Aims.The survey has been extended toward galaxies with lower FIR flux densities in order to confirm this correlation and to discover additional maser sources for relevant follow-up interferometric studies.Methods.A sample of 41 galaxies with 30 Jy $< S_{\rm 100\,\mu m} <$ 50 Jy and $\delta > -30$° was observed with the 100-m telescope at Effelsberg in a search for the 22 GHz water vapor line. The average 3$\sigma$ noise level of the survey is 40 mJy for a 1 km s$^{-1}$ channel, corresponding to a detection threshold for the isotropic maser luminosity of ~0.5 $L_{\odot}$ at a distance of 25 Mpc.Results.Two detections are reported: a megamaser with an isotropic luminosity, $L_{{\rm H_2 O}}$, of $\approx$35 $L_{\odot}$ in the Seyfert/Hii galaxy NGC 613 and a kilomaser with $L_{{\rm H_2 O}}$ $\approx$ 1 $L_{\odot}$ in the merger system NGC 520. The high luminosity and the presence of a Seyfert nucleus favor an association for NGC 613 with an active galactic nucleus. The kilomaser in NGC 520 was also detected with the Very Large Array, providing a position with subarcsecond accuracy. The H$_2$O emission, originating from a $\la$$0.02$ pc sized region with a brightness temperature $\ga$$10^{10}$ K (if the observed variations are intrinsic to the masing cloud(s)), is close to one of the two radio continuum sources located in the inner parsecs of NGC 520. The maser is most likely associated with a young supernova remnant ($SNR$), although an association with a low-luminosity AGN (LLAGN) cannot be ruled out. The maser detection rate, with 2 new maser sources out of 41 galaxies observed, is consistent with expectations extrapolated from the statistical properties of the $S_{\rm 100\,\mu m} >$ 50 Jy sample. The H$_2$O kilomasers are “subluminous”, while H$_2$O megamasers tend to be “superluminous” with respect to the FIR luminosity of their parent galaxy, when compared with sites of massive star formation in the Milky Way.http://dx.doi.org/10.1051/0004-6361:20078316. -
Article: The H I content of the recently discovered field dwarf galaxy APPLES 1
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ABSTRACT: We present observations in a search for neutral hydrogen associated with the recently detected field dwarf galaxy APPLES 1, performed with the Parkes radiotelescope. The observed radio spectrum shows no evident ($>$3$\sigma$ rms) line emission indicating an upper limit for the H i content of the galaxy of ~$10^{6}\:\hbox{$M_{\odot}$}$ and providing an upper value for the $M_{\rm HI}$/$L_{\rm B}$ ratio equal to 2.4 /. The low value of the H i content suggested by the observations, together with the galaxy optical morphology, might indicate that APPLES 1 is a dwarf spheroidal. This indication is in contrast with the evidence of recent star formation, which is typical for dwarf irregular galaxies. This may suggest that APPLES 1 belongs to the class of mixed dwarf irregular/spheroidal transition-type galaxies. We also conclude that the relatively low neutral gas mass in APPLES 1 can be explained by an extended and inefficient star formation process, without the need for a dramatic event such as enhanced star formation or a past encounter with a massive galaxy or galaxy group.http://dx.doi.org/10.1051/0004-6361:20053634. -
Article: New H$_\mathsf{2}$O masers in Seyfert and FIR bright galaxies
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ABSTRACT: Using the Effelsberg 100-m telescope, detections of four extragalactic water vapor masers are reported. Isotropic luminosities are ~50, 1000, 1 and 230 $L_{\odot}$ for Mrk 1066 (UGC 2456), Mrk 34, NGC 3556 and Arp 299, respectively. Mrk 34 contains by far the most distant and one of the most luminous water vapor megamasers so far reported in a Seyfert galaxy. The interacting system Arp 299 appears to show two maser hotspots separated by approximately 20´´. With these new results and even more recent data from Braatz et al. (2004, ApJ, 617, L29), the detection rate in our sample of Seyferts with known jet-Narrow Line Region interactions becomes 50% (7/14), while in star forming galaxies with high ($S_{\rm 100~\mu m}>50$ Jy) far infrared fluxes the detection rate is 22% (10/45). The jet-NLR interaction sample may not only contain “jet-masers” but also a significant number of accretion “disk-masers” like those seen in NGC 4258. A statistical analysis of 53 extragalactic H$_2$O sources (excluding the Galaxy and the Magellanic Clouds) indicates (1) that the correlation between IRAS Point Source and H$_2$O luminosities, established for individual star forming regions in the galactic disk, also holds for AGN-dominated megamaser galaxies; (2) that maser luminosities are not correlated with 60 $\mu$m/100 $\mu$m color temperatures; and (3) that only a small fraction of the luminous megamasers ($L_{\rm H_2O} > 100$ $L_{\odot}$) detectable with 100-m sized telescopes have so far been identified. The H$_2$O luminosity function (LF) suggests that the number of galaxies with 1 $L_{\odot} < L_{\rm H_2O} < 10$ $L_{\odot}$, the transition range between “kilomasers” (mostly star formation) and “megamasers” (active galactic nuclei), is small. The overall slope of the LF, ~-1.5, indicates that the number of detectable masers is almost independent of their luminosity. If the LF is not steepening at very high maser luminosities and if it is possible to find suitable candidate sources, H$_2$O megamasers at significant redshifts should be detectable even with present day state-of-the-art facilities.http://dx.doi.org/10.1051/0004-6361:20042175.
