- ID:
- ivo://CDS.VizieR/J/ApJ/877/154
- Title:
- H_2_CO TMRT obs. of Galactic molecular clouds
- Short Name:
- J/ApJ/877/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observations of the C-band 1_10_-1_11_ (4.8GHz) and Ku-band 2_11_-2_12_ (14.5GHz) K-doublet lines of H_2_CO and the C-band 1_10_-1_11_ (4.6GHz) line of H_2_^13^CO toward a large sample of Galactic molecular clouds, through the Shanghai Tianma 65m radio telescope (TMRT). Our sample with 112 sources includes strong H_2_CO sources from the TMRT molecular line survey at C-band and other known H_2_CO sources. All three lines are detected toward 38 objects (43 radial velocity components) yielding a detection rate of 34%. Complementary observations of their continuum emission at both C- and Ku-bands were performed. Combining spectral line parameters and continuum data, we calculate the column densities, the optical depths and the isotope ratio H_2_^12^CO/H_2_^13^CO for each source. To evaluate photon trapping caused by sometimes significant opacities in the main isotopologue's rotational mm-wave lines connecting our measured K-doublets, and to obtain ^12^C/^13^C abundance ratios, we used the RADEX non-LTE model accounting for radiative transfer effects. This implied the use of the new collision rates from Wiesenfeld & Faure. Also implementing distance values from trigonometric parallax measurements for our sources, we obtain a linear fit of ^12^C/^13^C=(5.08+/-1.10)D_GC_+(11.86+/-6.60), with a correlation coefficient of 0.58. D_GC_ refers to Galactocentric distances. Our ^12^C/^13^C ratios agree very well with the ones deduced from CN and C^18^O but are lower than those previously reported on the basis of H_2_CO, tending to suggest that the bulk of the H_2_CO in our sources was formed on dust grain mantles and not in the gas phase.
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- ID:
- ivo://CDS.VizieR/J/A+A/658/A5
- Title:
- Hercules A LOFAR and JVLA images
- Short Name:
- J/A+A/658/A5
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The prominent radio source Hercules A features complex structures in its radio lobes. Despite being one of the most comprehensively studied sources in the radio sky, the origin of the ring structures in the Hercules A radio lobes remains an open question. We present the first sub-arcsecond angular resolution images at low frequencies (<300MHZ) of Hercules A, made with the International LOFAR Telescope. With the addition of data from the Karl G. Jansky Very Large Array, we map the structure of the lobes from 144MHz to 7GHz. We explore the origin of the rings within the lobes of Hercules A, and test whether their properties are best described by a shock model where shock waves are produced by the jet propagating in the radio lobe, or an inner-lobe model in which the rings are formed by decelerated jetted plasma. From spectral index mapping, our large frequency coverage reveals that the curvature of the different ring spectra increases with distance away from the central active galactic nucleus. We demonstrate that the spectral shape of the rings is consistent with synchrotron aging, which speaks in favor of an inner-lobe model, where the rings are formed from the deposition of material from past periods of intermittent core activity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/394/1857
- Title:
- H_2_/HI ratio in galaxies
- Short Name:
- J/MNRAS/394/1857
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We revisit the mass ratio {eta}_galaxy_ between molecular hydrogen (H2) and atomic hydrogen (HI) in different galaxies from a phenomenological and theoretical viewpoint.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A44
- Title:
- HI absorption in flux-selected radio AGNs
- Short Name:
- J/A+A/575/A44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the HI 21cm absorption in a sample of 101 flux-selected radio AGN (S_1.4GHz_>50mJy) observed with the Westerbork Synthesis Radio Telescope (WSRT). We detect HI absorption in 32 objects (30% of the sample). In a previous paper, we performed a spectral stacking analysis on the radio sources, while here we characterize the absorption spectra of the individual detections using the recently presented busy function. The HI absorption spectra show a broad variety of widths, shapes, and kinematical properties. The full width half maximum (FWHM) of the busy function fits of the detected HI lines lies in the range 32km/s<FWHM<570km/s, whereas the full width at 20% of the peak absorption (FW20) lies in the range 63km/s<FW20<825km/s. The width and asymmetry of the profiles allows us to identify three groups: narrow lines (FWHM<100km/s), intermediate widths (100km/s<FWHM<200km/s), and broad profiles (FWHM>200km/s). We study the kinematical and radio source properties of each group, with the goal of identifying different morphological structures of HI. Narrow lines mostly lie at the systemic velocity and are likely produced by regularly rotating HI disks or gas clouds. More HI disks can be present among galaxies with lines of intermediate widths; however, the HI in these sources is more unsettled. We study the asymmetry parameter and blueshift/redshift distribution of the lines as a function of their width. We find a trend for which narrow profiles are also symmetric, while broad lines are the most asymmetric. Among the broadest lines, more lines appear blueshifted than redshifted, similarly to what was found by previous studies. Interestingly, symmetric broad lines are absent from the sample. We argue that if a profile is broad, it is also asymmetric and shifted relative to the systemic velocity because it is tracing unsettled HI gas. In particular, besides three of the broadest (up to FW20=825km/s) detections, which are associated with gas-rich mergers, we find three new cases of profiles with blueshifted broad wings (with FW20>500km/s) in high radio power AGN. These detections are good candidates for being HI outflows. Together with the known cases of outflows already included in the sample (3C 293 and 3C 305), the detection rate of HI outflows is 5% in the total radio AGN sample. Because of the effects of spin temperature and covering factor of the outflowing gas, this fraction could represent a lower limit. However, if the relatively low detection rate is confirmed by more detailed observations, it would suggest that, if outflows are a characteristic phenomenon of all radio AGN, they would have a short depletion timescale compared to the lifetime of the radio source. This would be consistent with results found for some of the outflows traced by molecular gas. Using stacking techniques, in our previous paper we showed that compact radio sources have higher {tau}, FWHM, and column density than extended sources. In addition, here we find that blueshifted and broad/asymmetric lines are more often present among compact sources. In good agreement with the results of stacking, this suggests that unsettled gas is responsible for the larger stacked FWHM detected in compact sources. Therefore in such sources the HI is more likely to be unsettled. This may arise as a result of jet-cloud interactions, as young radio sources clear their way through the rich ambient gaseous medium.
- ID:
- ivo://CDS.VizieR/J/ApJ/722/367
- Title:
- HI clouds in Quadrant I of the Milky Way
- Short Name:
- J/ApJ/722/367
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using 21cm HI observations from the Parkes Radio Telescope's Galactic All-Sky Survey, we measure 255 HI clouds in the lower Galactic halo that are located near the tangent points at 16.9<=l<=35.3{deg} and |b|<~20{deg}. The clouds have a median mass of 700M_{sun}_ and a median distance from the Galactic plane of 660pc.
- ID:
- ivo://CDS.VizieR/J/ApJ/626/887
- Title:
- HI clouds in Southern Galactic Plane Survey
- Short Name:
- J/ApJ/626/887
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an automated routine to search for HI self-absorption features within the Southern Galactic Plane Survey (SGPS). The data were taken with the Australia Telescope Compact Array (ATCA) and the Parkes Radio Telescope and encompass 3{deg}x105{deg} of sky in the Galactic plane. We apply our routine to this entire region and derive spin temperatures and column densities for 70 of the larger HISA complexes, finding spin temperatures ranging from 6 to 41K with HI number densities of a few cm^-3^. These "missing link" clouds fill in the spin temperature and density gaps between dense molecular clouds and diffuse atomic clouds. We compare the HI emission with ^12^CO emission and find that 60% of detected HI self-absorption is correlated in space and in velocity with a molecular counterpart. This is potentially due to a molecular/atomic gas transition. We also compare HI self-absorption with Galactic spiral arms and discuss the possibility of using it as a spiral arm tracer.
- ID:
- ivo://CDS.VizieR/J/MNRAS/462/4197
- Title:
- HI 21-cm absorption in redshifted galaxies
- Short Name:
- J/MNRAS/462/4197
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The star-forming reservoir in the distant Universe can be detected through HI 21-cm absorption arising from either cool gas associated with a radio source or from within a galaxy intervening the sightline to the continuum source. In order to test whether the nature of the absorber can be predicted from the profile shape, we have compiled and analysed all of the known redshifted (z>=0.1) HI 21-cm absorption profiles. Although between individual spectra there is too much variation to assign a typical spectral profile, we confirm that associated absorption profiles are, on average, wider than their intervening counterparts. It is widely hypothesized that this is due to high-velocity nuclear gas feeding the central engine, absent in the more quiescent intervening absorbers. Modelling the column density distribution of the mean associated and intervening spectra, we confirm that the additional low optical depth, wide dispersion component, typical of associated absorbers, arises from gas within the inner parsec. With regard to the potential of predicting the absorber type in the absence of optical spectroscopy, we have implemented machine learning techniques to the 55 associated and 43 intervening spectra, with each of the tested models giving a >=80 per cent accuracy in the prediction of the absorber type. Given the impracticability of follow-up optical spectroscopy of the large number of 21-cm detections expected from the next generation of large radio telescopes, this could provide a powerful new technique with which to determine the nature of the absorbing galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJS/245/3
- Title:
- HI 21cm and OH 18cm absorption search with the GBT
- Short Name:
- J/ApJS/245/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a large search for intrinsic HI 21cm and OH 18cm absorption in 145 compact radio sources in the redshift range 0.02<z<3.8 with the Green Bank Telescope. We redetect HI 21cm absorption toward six known absorption systems, but detect no new HI or OH absorption in 102 interference-free sources. Seventy-nine sources have not previously been observed for HI 21cm absorption. We recover a mean optical depth limit of {tau}_3{sigma}_<0.023 for all the nondetections in the survey. Our results do not support the high intrinsic absorption rates found by previous studies in compact radio sources at low redshift. Our results do, however, support the hypothesis proposed by Curran+ (2019MNRAS.484.1182C) that high ultraviolet (UV) luminosity active galactic nuclei do not show intrinsic HI 21cm absorption, confirming a threshold of L_UV_=10^23^W/Hz, above which our intrinsic absorption fraction is zero (54 sources). The exact nature of the UV luminosity effect on HI absorption systems remains ambiguous. We additionally find no statistical correlation between the 1.4GHz radio luminosity or the source size and the 21cm absorption detection rate. We attribute the lack of intrinsic absorption in our survey to the UV luminosity effect caused by an optical selection bias and a decreased column density sensitivity with increasing redshift due to lower radio continuum flux densities, high radio frequency interference, and higher telescope system temperatures at low frequencies.
- ID:
- ivo://CDS.VizieR/J/ApJS/173/85
- Title:
- HI 21cm forbidden-velocity wings
- Short Name:
- J/ApJS/173/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for faint HI 21cm emission line wings at velocities forbidden by Galactic rotation in the Galactic plane using the Leiden/Dwingeloo HI Survey data and the HI Southern Galactic Plane Survey data. These "forbidden-velocity wings" (FVWs) appear as protruding excessive emission in comparison with their surroundings in limited (>~2{deg}) spatial regions over velocity extents of more than ~20km/s in large-scale (l,v) diagrams. Their high velocities imply that there should be some dynamical phenomena associated. We have identified 87 FVWs. We present their catalog and discuss their distribution and statistical properties. We found that 85% of FVWs are not coincident with known supernova remnants (SNRs), galaxies, or high-velocity clouds. Their natures are currently unknown.
- ID:
- ivo://CDS.VizieR/J/AJ/133/1104
- Title:
- HI 21cm observations of Pegasus galaxies
- Short Name:
- J/AJ/133/1104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present neutral hydrogen observations of 54 galaxies in the Pegasus Cluster. The observations include single-dish HI measurements, obtained with the Arecibo telescope for all 54 galaxies in the sample, as well as HI images obtained with the Very Large Array (VLA) for 10 of these.
