- ID:
- ivo://CDS.VizieR/J/ApJ/770/L4
- Title:
- HI clouds around the Galactic Center
- Short Name:
- J/ApJ/770/L4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a population of small, high-velocity, atomic hydrogen clouds, loops, and filaments found above and below the disk near the Galactic center. The objects have a mean radius of 15pc, velocity widths of ~14km/s, and are observed at |z| heights up to 700pc. The velocity distribution of the clouds shows no signature of Galactic rotation. We propose a scenario where the clouds are associated with an outflow from a central star-forming region at the Galactic center. We discuss the clouds as entrained material traveling at ~200km/s in a Galactic wind.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/157/241
- Title:
- HI clouds in LITTLE THINGS dwarf irregular galaxies
- Short Name:
- J/AJ/157/241
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify 814 discrete H I clouds in 40 dwarf irregular galaxies from the LITTLE THINGS survey using an automated cloud-finding algorithm. The cloud masses range from ~10^3^ to 10^7^ M_{sun}_, have a surface density averaged over all of the clouds of ~9.65 M_{sun}_/pc^2^, and constitute 2%-53% of the total H I mass of the host galaxy. For individual clouds, the mass including He varies with cloud radius as logM_gas_=(2.11+/-0.04)xlogR_cl_+(0.78+/-0.08) and the internal velocity dispersion varies as logV_disp_=0.5xlogR_cl_-0.57+/-0.21. The H I clouds tend to be in the outer regions of the galaxies, with 72% of the galaxies having more than 70% of their clouds outside one disk scale length and 32% of the galaxies having more than 50% of their clouds outside the radius encircling the H II emission. Thirty-six percent of the clouds are essentially non-self-gravitating from H I alone, with a virial parameter that exceeds {alpha}_vir_~10, and 5% have {alpha}_vir_=<2. We estimate the missing molecular mass, based on the total star formation rate and a typical molecular consumption time of 2 Gyr, as observed in CO-rich galaxies. The resulting molecular fraction has a value averaged over the galaxies of 0.23 and correlates with both the surface density of star formation and the fraction of H I clouds in the outer regions. We conclude that a significant fraction of the inner parts of these dwarf galaxy disks is in the form of dark molecular gas, and that this fraction could be high enough to make the inner disks mildly gravitationally unstable as a precursor to star formation.
- 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/MNRAS/465/588
- Title:
- HI 21-cm absorption survey of QSO-galaxy pairs
- Short Name:
- J/MNRAS/465/588
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from our survey of HI 21-cm absorption, using Giant Metrewave Radio Telescope, Very Large Array and Westerbork Radio Synthesis Telescope, in a sample of 55 z<0.4 galaxies towards radio sources with impact parameters (b) in the range ~0-35kpc. In our primary sample (defined for statistical analyses) of 40 quasar-galaxy pairs, probed by 45 sightlines, we have found seven HI 21-cm absorption detections, two of which are reported here for the first time. Combining our primary sample with measurements having similar optical depth sensitivity ({int}{tau}dv<=0.3km/s) from the literature, we find a weak anti-correlation (rank correlation coefficient =-0.20 at 2.42{sigma} level) between {int}{tau}dv and b, consistent with previous literature results. The covering factor of HI 21-cm absorbers (C21) is estimated to be 0.24^+0.12^_-0.08_ at b<=15kpc and 0.06^+0.09^_-0.04_ at b=15-35kpc. {int}{tau}dv and C_21_ show similar declining trend with radial distance along the galaxy's major axis and distances scaled with the effective HI radius. There is also tentative indication that most of the HI 21-cm absorbers could be co-planar with the extended HI discs. No significant dependence of {int}{tau}dv and C_21_ on galaxy luminosity, stellar mass, colour and star formation rate is found, though the HI 21-cm absorbing gas cross-section may be larger for the luminous galaxies. The higher detection rate (by a factor of ~4) of HI 21-cm absorption in z<1 damped Lyman-{alpha} systems compared to the quasar-galaxy pairs indicates towards small covering factor and patchy distribution of cold gas clouds around low-z galaxies.
- 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/A+A/650/A76
- Title:
- HI content in Coma cluster substructure
- Short Name:
- J/A+A/650/A76
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Galaxy clusters are some of largest structures in the universe. These very dense environments tend to be home to higher numbers of evolved galaxies than found in lower-density environments. It is well known that dense environments can influence the evolution of galaxies through the removal of the neutral gas (HI) reservoirs that fuel star formation. It is unclear which environment has a stronger effect: the local environment (i.e. the substructure within the cluster), or the cluster itself. Using the new HI data from the Westerbork Coma Survey, we explore the average HI content of galaxies across the cluster comparing galaxies that reside in substructure to those that do not. We applied the Dressler-Shectman test to our newly compiled redshift catalogue of the Coma cluster to search for substructure. With so few of the Coma galaxies directly detected in HI, we used the HI stacking technique to probe the average HI content below what can be directly detected. Using the Dressler-Shectman test, we find 15 substructures within the footprint of the Westerbork Coma Survey. We compare the average HI content for galaxies within substructure to those not in substructure. Using the HI stacking technique, we find that those Coma galaxies not detected in HI are more than 10-50 times more HI deficient than expected, which supports the scenario of an extremely efficient and rapid quenching mechanism. By studying the galaxies that are not directly detected in HI, we also find Coma to be more HI deficient than previously thought.
- ID:
- ivo://CDS.VizieR/J/MNRAS/447/1531
- Title:
- HI data collection update
- Short Name:
- J/MNRAS/447/1531
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cosmic Flows is an international multi-element project with the goal to map motions of galaxies in the local Universe. Kinematic information from observations in the radio HI line and photometry at optical or near-infrared bands are acquired to derive the large majority of distances that are obtained through the luminosity-linewidth or Tully-Fisher relation. This paper gathers additional observational radio data, frequently unpublished, retrieved from the archives of Green Bank, Parkes and Arecibo telescopes. Extracted HI profiles are consistently processed to produce linewidth measurements. Our current 'All-Digital HI Catalog' contains a total of 20343 HI spectra for 17738 galaxies with 14 802 galaxies with accurate linewidth measurement useful for Tully-Fisher galaxy distances. This addition of 4117 new measurements represents an augmentation of 34 percent compared to our last release.
