- ID:
- ivo://CDS.VizieR/J/MNRAS/459/220
- Title:
- Optical redshifts of OH- and HI-emitting galaxies
- Short Name:
- J/MNRAS/459/220
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- OH megamasers (OHMs) are rare, luminous molecular masers that are typically observed in (ultra) luminous infrared galaxies and serve as markers of major galaxy mergers. In blind emission line surveys such as the Arecibo Legacy Fast Arecibo L-Band Feed Array (ALFALFA) survey for neutral hydrogen (HI), OHMs at z~0.2 can mimic z~0.05 HI lines. We present the results of optical spectroscopy of ambiguous HI detections in the ALFALFA 40 per cent data release detected by the Wide Field Infrared Survey Explorer (WISE) but with uncertain optical counterparts. The optical redshifts, obtained from observations at the Apache Point Observatory, revealed five new OHMs and identified 129 HI optical counterparts. 60 candidates remain ambiguous. The new OHMs are the first detected in a blind spectral line survey. The number of OHMs in ALFALFA is consistent with predictions from the OH luminosity function. Additionally, the mid-infrared magnitudes and colours of the OHM host galaxies found in a blind survey do not seem to differ from those found in previous targeted surveys. This validates the methods used in previous IR-selected OHM surveys and indicates there is no previously unknown OHM-producing population at z~0.2. We also provide a method for future surveys to separate OH megamasers from 99 per cent of HI line emitters without optical spectroscopy by using WISE infrared colours and magnitudes. Since the fraction of OHMs found in flux-limited HI surveys is expected to increase with the survey's redshift, this selection method can be applied to future flux-limited high-redshift hydrogen surveys.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/161/71
- Title:
- Paramaters for 40 LITTLE THINGS galaxies
- Short Name:
- J/AJ/161/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar, gaseous and young stellar disks in the LITTLE THINGS sample of nearby dwarf irregular galaxies are fitted with functions to search for correlations between the parameters. We find that the HI radial profiles are generally flatter in the center and fall faster in the outer regions than the V-band profiles, while young stars are more centrally concentrated, especially if the HI is more centrally flat. This pattern suggests that the HI is turning into molecules in the center, and the molecular clouds are forming stars and FUV. A model that assumes the molecular surface density is proportional to the total gas surface density to a power of 1.5 or 2, in analogy with the Kennicutt-Schmidt relation, reproduces the relationship between the ratio of the visible to the HI scale length and the HI Sersic index. The molecular fraction is estimated as a function of radius for each galaxy by converting the FUV to a molecular surface density using conventional calibrations. The average molecular fraction inside 3RD is 23%{+/-}17%. However, the break in the stellar surface brightness profile has no unified tracer related to star formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/15
- Title:
- Parameters for the 58 {tau}HI(v) sightlines
- Short Name:
- J/ApJ/899/15
- Date:
- 14 Mar 2022 07:09:23
- Publisher:
- CDS
- Description:
- Resolving the phase structure of neutral hydrogen (HI) is crucial for understanding the life cycle of the interstellar medium (ISM). However, accurate measurements of HI temperature and density are limited by the availability of background continuum sources for measuring HI absorption. Here we test the use of deep learning for extracting HI properties over large areas without optical depth information. We train a 1D convolutional neural network using synthetic observations of 3D numerical simulations of the ISM to predict the fraction (f_CNM_) of cold neutral medium (CNM) and the correction to the optically thin HI column density for optical depth (R_H_I__) from 21cm emission alone. We restrict our analysis to high Galactic latitudes (|b|>30{deg}), where the complexity of spectral line profiles is minimized. We verify that the network accurately predicts f_CNM_ and R_H_I__ by comparing the results with direct constraints from 21cm absorption. By applying the network to the GALFA-HI survey, we generate large-area maps of f_CNM_ and R_H_I__. Although the overall contribution to the total HI column of CNM-rich structures is small (~5%), we find that these structures are ubiquitous. Our results are consistent with the picture that small-scale structures observed in 21cm emission aligned with the magnetic field are dominated by CNM. Finally, we demonstrate that the observed correlation between HI column density and dust reddening (E(B-V)) declines with increasing R_H_I__, indicating that future efforts to quantify foreground Galactic E(B-V) using HI, even at high latitudes, should increase fidelity by accounting for HI phase structure.
- ID:
- ivo://CDS.VizieR/VIII/8A
- Title:
- Parkes High-Latitude H I Survey
- Short Name:
- VIII/8A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This survey consists of HI 21-cm spectra covering the southern sky with absolute galactic latitude |b|>=10 degrees and declination dec<=-30 degrees. The observations were made with the Parkes Radio Observatory (CSIRO) 60-foot telescope. The receiver back end was the Parkes 64-channel spectrometer. The velocity resolution was 7km/s (33kHz) and the beamwidth (HPBW) was 48arcmin. Drift scans at constant declination were used with continuous integration in right ascension for -80<=declination<=-30 degrees. For declination<-80 degrees a grid of positions spaced 1 degree apart in declination and one beam-width apart in right ascension were observed. The survey was made in two parts. Part 1 included b>=-25 degrees, |b|>=10 degrees and declination dec<=-30 degrees. Part 2 included b<=-25 degrees and dec<=-30 degrees. The scans in Part 1 were spaced at 1 degree intervals in declination and the velocity coverage was from -148 to +300km/s. The scans in Part 2 were spaced at 2 degrees and the velocity coverage was from -230 to +218km/s. Each spectrum or record consists of a header followed by 64 antenna temperatures. The header contains the galactic longitude, galactic latitude, right ascension, declination, central velocity (LSR), and quality factor. The catalog contains a total of 9891 spectra.
- ID:
- ivo://CDS.VizieR/J/AJ/122/3155
- Title:
- Peculiar HI cloud near galactic plane
- Short Name:
- J/AJ/122/3155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An H I cloud with a double-lobed structure and a radial velocity of +50km/s has been found near l=92{deg}, b=-4{deg} in a low-resolution H I survey carried out at the Dominion Radio Astrophysical Observatory (DRAO). This velocity is forbidden for circular Galactic rotation. Because of its unusual morphology and small variation in radial velocity over the cloud, further observations of the area were made with the DRAO Synthesis Telescope, both in the H I line and in the radio continuum. The cloud has dimensions of about 3.3{deg}x0.5{deg}, and has a morphology somewhat similar to high-velocity H I clouds (HVCs). Several possible associations with other objects are examined in this paper. A variable inverted-spectrum radio continuum source exists near the morphological center of the H I cloud. It is probably a rare example of a gigahertz peaked spectrum (GPS) extragalactic source having a peak above 5GHz. A luminous B star is found close to the peculiar H I cloud, and the cloud is also located near the center of an H I supershell, supposedly located at a distance of about 9kpc. Energetic and other considerations lead to the conclusion that the cloud is probably not related to the HVC phenomenon nor to any of the above objects but is a relic of a nearby (D~1kpc) supernova event, all other evidence of which has now dissipated. Maps of continuum radio emission (at 1420 and 408MHz) in the area around the cloud are presented, as well as lists of continuum radio sources. A few isolated high-velocity knots of H I emission have also been detected in the vicinity of the cloud.
- ID:
- ivo://CDS.VizieR/J/ApJ/793/132
- Title:
- Perseus cloud sources Gaussian parameters
- Short Name:
- J/ApJ/793/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Arecibo Observatory, we have obtained neutral hydrogen (HI) absorption and emission spectral pairs in the direction of 26 background radio continuum sources in the vicinity of the Perseus molecular cloud. Strong absorption lines were detected in all cases, allowing us to estimate spin temperature (T_s_) and optical depth for 107 individual Gaussian components along these lines of sight. Basic properties of individual H I clouds (spin temperature, optical depth, and the column density of the cold and warm neutral medium (CNM and WNM), respectively) in and around Perseus are very similar to those found for random interstellar lines of sight sampled by the Millennium H I survey. This suggests that the neutral gas found in and around molecular clouds is not atypical. However, lines of sight in the vicinity of Perseus have, on average, a higher total H I column density and the CNM fraction, suggesting an enhanced amount of cold H I relative to an average interstellar field. Our estimated optical depth and spin temperature are in stark contrast with the recent attempt at using Planck data to estimate properties of the optically thick H I. Only ~15% of lines of sight in our study have a column density weighted average spin temperature lower than 50 K, in comparison with >~85% of Planck's sky coverage. The observed CNM fraction is inversely proportional to the optical depth weighted average spin temperature, in excellent agreement with the recent numerical simulations by Kim et al. (2014ApJ...786...64K). While the CNM fraction is, on average, higher around Perseus relative to a random interstellar field, it is generally low, between 10%-50%. This suggests that extended WNM envelopes around molecular clouds and/or significant mixing of CNM and WNM throughout molecular clouds are present and should be considered in the models of molecule and star formation. Our detailed comparison of H I absorption with CO emission spectra shows that only 3 of the 26 directions are clear candidates for probing the CO-dark gas as they have N(H I)>10^21^/cm2 yet no detectable CO emission.
- ID:
- ivo://CDS.VizieR/J/MNRAS/416/2
- Title:
- Photodissociation regions in M33
- Short Name:
- J/MNRAS/416/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive total (atomic + molecular) hydrogen densities in giant molecular clouds (GMCs) in the nearby spiral galaxy M33 using a method that views the atomic hydrogen near regions of recent star formation as the product of photodissociation. Far-ultraviolet (FUV) photons emanating from a nearby OB association produce a layer of atomic hydrogen on the surfaces of nearby GMCs. Our approach provides an estimate of the total hydrogen density in these GMCs from observations of the excess FUV emission that reaches the GMC from the OB association and of the excess 21-cm radio HI emission produced after these FUV photons convert H2 into HI on the GMC surface. The method provides an alternative approach to the use of CO emission as a tracer of H2 in GMCs and is especially sensitive to a range of densities well below the critical density for CO(1-0) emission.
- ID:
- ivo://CDS.VizieR/J/AJ/105/1271
- Title:
- Pisces-Perseus supercluster. VI
- Short Name:
- J/AJ/105/1271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New results are presented of Arecibo observations in the 21 cm line of 765 galaxies with declinations between 15.5 deg and 21.5 deg, in the Pisces-Perseus supercluster zone. If considered independently on the neighboring parts of the sky, this region, to the South of the supercluster ridge, shows significantly less evidence of structure on large scales in excess of 30 Mpc, contrasting substantially with the characteristics of the declination zones immediately to the North.
- ID:
- ivo://CDS.VizieR/J/AJ/143/133
- Title:
- Properties of dwarf galaxies from the ALFALFA survey
- Short Name:
- J/AJ/143/133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the global properties of the stellar and HI components of 229 low HI mass dwarf galaxies extracted from the ALFALFA survey ({alpha}.40; Haynes et al., 2011, Cat. J/AJ/142/170), including a complete sample of 176 galaxies with HI masses<10^7.7^M_{sun}_and HI line widths<80km/s. Sloan Digital Sky Survey (SDSS; Cat . II/294 superseded by Cat. V/139) data are combined with photometric properties derived from Galaxy Evolution Explorer (GALEX; GR5, Cat. II/312) to derive stellar masses (M_*_) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M_*_ obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M_*_<~10^8^M_{sun}_ is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper HI mass limit yields the selection of a sample with lower gas fractions for their M_*_ than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have HI depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that HI disks are more extended than stellar ones.
- ID:
- ivo://CDS.VizieR/J/MNRAS/416/2437
- Title:
- Quantified H I morphology of WHISP sample
- Short Name:
- J/MNRAS/416/2437
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The morphology of the atomic hydrogen (HI) disc of a spiral galaxy is the first component to be disturbed by a gravitational interaction such as a merger between two galaxies. We use a simple parametrization of the morphology of HI column density maps of the Westerbork observations of neutral Hydrogen in Irregular and SPiral galaxies (WHISP) project to select those galaxies that are likely undergoing a significant interaction. Merging galaxies occupy a particular part of parameter space defined by Asymmetry (A), the relative contribution of the 20 per cent brightest pixels to the second-order moment of the column density map (M20) and the distribution of the second-order moment over all the pixels (GM). Based on their HI morphology, we find that 13 per cent of the WHISP galaxies are in an interaction (Concentration-M20) and only 7 per cent are based on close companions in the data cube. This apparent discrepancy can be attributed to the difference in visibility time-scales: mergers are identifiable as close pairs for 0.5 Gyr but are identifiable for ~1Gyr by their disturbed HI morphology. Expressed as volume merger rates, the two estimates agree very well: 7 and 6.8x10^-3^mergers/Gyr/Mpc^3^ for paired and morphologically disturbed HI discs, respectively.
