- ID:
- ivo://CDS.VizieR/J/ApJ/669/424
- Title:
- H2O maser emissions of IRAS 19134+2131
- Short Name:
- J/ApJ/669/424
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Very Long Baseline Array at six epochs, we have observed H_2_O maser emission in the preplanetary nebula IRAS 19134+2131 (I19134), in which the H_2_O maser spectrum has two groups of emission features separated in radial velocity by ~100km/s. We also obtained optical images of I19134 with the Hubble Space Telescope to locate the bipolar reflection nebula in this source for the first time.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/430/1309
- Title:
- H_2_O masers in AFGL 2591 VLA 3-N
- Short Name:
- J/MNRAS/430/1309
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we analyse multi-epoch very long baseline interferometry water maser observations carried out with the Very Long Baseline Array towards the high-mass star-forming region AFGL 2591. We detected maser emission associated with the radio continuum sources VLA 2 and VLA 3. In addition, a water maser cluster, VLA 3-N, was detected ~0.5arcsec north of VLA 3. We concentrate the discussion of this paper on the spatio-kinematical distribution of the water masers towards VLA 3-N. The water maser emission towards the region VLA 3-N shows two bow-shock-like structures, northern and southern, separated from each other by ~100mas (~330AU). The spatial distribution and kinematics of the water masers in this cluster have persisted over a time span of 7yr. The northern bow shock has a somewhat irregular morphology, while the southern one has a remarkably smooth morphology. We measured the proper motions of 33 water maser features, which have an average proper motion velocity of ~1.3mas/yr (~20km/s). The morphology and the proper motions of this cluster of water masers show systematic expanding motions that could imply one or two different centres of star formation activity. We made a detailed model for the southern structure, proposing two different kinematic models to explain the three-dimensional spatio-kinematical distribution of the water masers: (1) a static central source driving the two bow-shock structures and (2) two independent driving sources, one of them exciting the northern bow-shock structure, and the other one, a young runaway star moving in the local molecular medium exciting and moulding the remarkably smoother southern bow-shock structure. Future observations will be necessary to discriminate between the two scenarios, in particular by identifying the still unseen driving source(s).
- ID:
- ivo://CDS.VizieR/J/A+A/291/261
- Title:
- H2O masers in HII regions
- Short Name:
- J/A+A/291/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a survey of 22.2GHz H2O maser emission towards a large sample of HII regions (427) detected in hydrogen recombination lines (Lockman) are presented. The sample favours classical HII regions with large excitation parameter. We found 68 water maser sources, 17 of which are new detections. Adding the detections found in the literature, the total number of masers associated with the sample is 80. The overall maser percentage is low (19%), much less than what found in samples of ultracompact (UC) HII regions. The percentage changes if we divide our sample into two sub-classes: HII regions known to have ultracompact components (i.e. where a younger generation of star formation is also present) and the rest. In the first sub-class the maser percentage is 28%, in the second 15%. The total number of masers in HII regions where no UC component has been (so far) reported is 43. This value is greater than that expected from the ratio between the lifetime of the HII region (10^6^yr) and that of the maser phase, even assuming a maser lifetime as long as 10^5^yr. This implies that maser excitation (and star formation) occurs several times in the lifetime of the same star forming complex. From 410 positions observed, 230 can be associated with a high degree of confidence to an IRAS Point Source. We expect that most of the HII regions not associated with IRAS PS are diffuse regions in the last phases of their evolution. The percentage of water masers in this sub-class is very low: 8%. The number of masers with no counterpart in the Lockman sample (and above Dec=-30{deg}) is very large: 334. This number most probably reflects the extreme high density conditions known to exist in the earliest phases of an HII region, which strongly reduce its radio continuum and line emission. The analysis of a homogeneous sample of classical HII regions allows to confirm in a quantitative fashion the well known result that the maser phenomenon occurs during the earliest phase of the evolution of a massive star and that it fades away as the HII region evolves into the diffuse stage.
- ID:
- ivo://CDS.VizieR/J/ApJS/155/577
- Title:
- H2O masers in W49 North and Sagittarius B2
- Short Name:
- J/ApJS/155/577
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Very Large Array (VLA) of the National Radio Astronomy Observatory in the A and B configurations, we have obtained simultaneous high-resolution observations of both the 22GHz H2O maser lines as well as the 22GHz continuum for the H II regions W49N and Sagittarius B2.
- ID:
- ivo://CDS.VizieR/J/A+AS/127/181
- Title:
- H2O maser sources new detections
- Short Name:
- J/A+AS/127/181
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of H_2_O maser sources on the 13.7m radio telescope of Purple Mountain Observatory from 1990 Aug. to 1994 Jan. are summarized. For searching new water masers, the total number of search candidates is about 360, with 110 objects detected. Among them are 96 new detections. A list of the new detections and their spectra are presented.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A42
- Title:
- H2O megamaser galaxies radio continuum 5GHz data
- Short Name:
- J/A+A/624/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc accretion disks. Because of the small linear and angular scales involved, this alignment has not yet been checked in a sufficient number of low luminosity active galactic nuclei (LLAGNs). The project examines the validity of this paradigm by measuring the radio continuum on the same physical scale as the accretion disks to investigate any possible connection between these disks and the radio continuum. We observed a sample of 18 LLAGNs in the 4.8GHz (6cm) radio continuum using the Very Long Baseline Array (VLBA) with 3.3-6.5ms resolution. The sources were selected to show both an edge-on accretion disk revealed by 22GHz H_2_O megamaser emission and signatures of a radio jet. Furthermore, the sources were previously detected in 33GHz radio continuum observations made with the Very Large Array. Five out of 18 galaxies observed were detected at 8{sigma} or higher levels (Mrk 0001, Mrk 1210, Mrk 1419, NGC 2273, and UGC 3193). While these five sources are known to have maser disks, four of them exhibit a maser disk with known orientation. For all four of these sources, the radio continuum is misaligned relative to the rotation axis of the maser disk, but with a 99.1% confidence level, the orientations are not random and are confined to a cone within 32{deg} of the maser disk's normal. Among the four sources the misalignment of the radio continuum with respect to the normal vector to the maser disk is smaller when the inner radius of the maser disk is larger. Furthermore, a correlation is observed between the 5GHz VLBA radio continuum and the [OIII] luminosity and also with the H_2_O maser disk's inner radius.
- ID:
- ivo://CDS.VizieR/J/MNRAS/470/1462
- Title:
- HOPS. III. Dense molecular gas properties
- Short Name:
- J/MNRAS/470/1462
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The H_2_O Southern Galactic Plane Survey (HOPS) has mapped 100deg^2^ of the Galactic plane for water masers and thermal molecular line emission using the 22m Mopra telescope. We describe the automated spectral-line fitting pipelines used to determine the properties of emission detected in HOPS data cubes, and use these to derive the physical and kinematic properties of gas in the survey. A combination of the angular resolution, sensitivity, velocity resolution and high critical density of lines targeted make the HOPS data cubes ideally suited to finding precursor clouds to the most massive and dense stellar clusters in the Galaxy. We compile a list of the most massive HOPS ammonia regions and investigate whether any may be young massive cluster progenitor gas clouds. HOPS is also ideally suited to trace the flows of dense gas in the Galactic Centre. We find the kinematic structure of gas within the inner 500pc of the Galaxy is consistent with recent predictions for the dynamical evolution of gas flows in the centre of the Milky Way. We confirm a recent finding that the dense gas in the inner 100pc has an oscillatory kinematic structure with characteristic length-scale of 20pc, and also identify similar oscillatory kinematic structure in the gas at radii larger than 100pc. Finally, we make all of the above fits and the remaining HOPS data cubes across the 100deg^2^ of the survey available to the community.
- ID:
- ivo://CDS.VizieR/J/A+A/560/A73
- Title:
- Horsehead H2CO and CH3OH 30m and PdBI maps
- Short Name:
- J/A+A/560/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Theoretical models and laboratory experiments show that CH_3_OH is efficiently formed on cold grain surfaces through the successive hydrogenation of CO, forming HCO and H_2_CO as intermediate species. In cold cores and low UV-field illumination photo-dissociation regions (PDRs) the ices can be released into the gas-phase through nonthermal processes such as photodesorption, which considerably increases their gas-phase abundances. We investigate the dominant formation mechanism of H_2_CO and CH_3_OH in the Horsehead PDR and its associated dense core.
- ID:
- ivo://CDS.VizieR/J/MNRAS/416/1764
- Title:
- H_2_O Southern Galactic Plane Survey (HOPS)
- Short Name:
- J/MNRAS/416/1764
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present first results of the H_2_O Southern Galactic Plane Survey (HOPS), using the Mopra Radio Telescope with a broad-band backend and a beam size of about 2arcmin. We have observed 100deg^2^ of the southern Galactic plane at 12mm (19.5-27.5GHz), including spectral line emission from H_2_O masers, multiple metastable transitions of ammonia, cyanoacetylene, methanol and radio recombination lines. In this paper, we report on the characteristics of the survey and H2O maser emission. We find 540 H_2_O masers, of which 334 are new detections.
- ID:
- ivo://CDS.VizieR/J/MNRAS/426/1972
- Title:
- H_2_O Southern Galactic Plane Survey, HOPS. II
- Short Name:
- J/MNRAS/426/1972
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The H2O Southern Galactic Plane Survey (HOPS) has mapped a 100{deg} strip of the Galactic plane (-70{deg}>l>30{deg}, |b|<0.5{deg}) using the 22m Mopra antenna at 12mm wavelengths. Observations were conducted in on-the-fly mode using the Mopra spectrometer (MOPS), targeting water masers, thermal molecular emission and radio-recombination lines. Foremost among the thermal lines are the 23GHz transitions of NH3 J,K=(1,1) and (2,2), which trace the densest parts of molecular clouds (n>10^4^cm^-3^). In this paper, we present the NH_3_(1,1) and (2,2) data, which have a resolution of 2arcmin and cover a velocity range of +/-200km/s.