- 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.
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Search Results
- 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 II/294 superseded by Cat.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.
- ID:
- ivo://CDS.VizieR/J/MNRAS/427/3159
- Title:
- Quantified HI morphology. VI. NUV/FUV
- Short Name:
- J/MNRAS/427/3159
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extended ultraviolet (XUV) discs have been found in a substantial fraction of late-type - S0, spiral and irregular - galaxies. Similarly, most late-type spirals have an extended gas disc, observable in the 21-cm radio line (HI). The morphology of galaxies can be quantified well using a series of scale-invariant parameters; concentration-asymmetry-smoothness (CAS), Gini, M_20_, and G_M_ parameters. In this series of papers, we apply these to HI column density maps to identify mergers and interactions, lopsidedness and now XUV discs. In this paper, we compare the quantified morphology and effective radius (R_50_) of the Westerbork observations of neutral Hydrogen in Irregular and SPiral galaxies Project (WHISP) HI maps to those of far- and near-ultraviolet images obtained with GALEX, to explore how close the morphology and scales of HI and UV in these discs correlate. We find that XUV discs do not stand out by their effective radii in UV or HI. However, the concentration index in far-ultraviolet (FUV) appears to select some XUV discs. And known XUV discs can be identified via a criterion using asymmetry and M_20_; 80 per cent of XUV discs are included but with 55 per cent contamination. This translates into 61 candidate XUV disc out of our 266 galaxies, 23 per cent consistent with previous findings. Otherwise, the UV and HI morphology parameters do not appear closely related.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A94
- Title:
- Radio continuum and gas reservoir in NGC 3998
- Short Name:
- J/A+A/592/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the nearby lenticular galaxy NGC 3998. This galaxy is known to host a low-power radio AGN with a kpc-size one-sided jet and a large, nearly polar HI disc. It is therefore a good system to study to understand the relation between the availability of cold-gas and the triggering of AGNs in galaxies. Our new WSRT data reveal two faint, S-shaped radio lobes extending out to ~10 kpc from the galaxy centre. Remarkably, we find that the inner HI disc warps back towards the stellar mid-plane in a way that mirrors the warping of the radio lobes. We suggest that the polar HI disc was accreted through a minor merger, and that the torques causing it to warp in the inner regions are also responsible for feeding the AGN. The "S" shape of the radio lobes would then be due to the radio jets adapting to the changing angular momentum of the accreted gas. The extended radio jets are likely poorly collimated, which would explain their quick fading and, therefore, their rarity in galaxies similar to NGC 3998. The fuelling of the central super-massive black hole is likely occurring via "discrete events", suggested by the observed variability of the radio core and the extremely high core dominance, which we attribute to the formation and ejection of a new jet resulting from a recent fuelling event.
- ID:
- ivo://CDS.VizieR/J/MNRAS/346/1103
- Title:
- Redshifts of damped Lyman{alpha} absorbers
- Short Name:
- J/MNRAS/346/1103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the evolution of the column density distribution, f(N,z), and total neutral hydrogen mass in high column density quasar absorbers using candidates from a recent high-redshift survey for damped Lyman{alpha} (DLA) and Lyman-limit system (LLS) absorbers.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A142
- Title:
- Reduced high-resolution HI and CO data cubes
- Short Name:
- J/A+A/592/A142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Intermediate-velocity clouds (IVCs) are HI halo clouds that are likely related to a Galactic fountain process. In-falling IVCs are candidates for the re-accretion of matter onto the Milky Way. Aims. We study the evolution of IVCs at the disk-halo interface, focussing on the transition from atomic to molecular IVCs. We compare an atomic IVC to a molecular IVC and characterise their structural differences in order to investigate how molecular IVCs form high above the Galactic plane. With high-resolution HI observations of the Westerbork Synthesis Radio Telescope and ^12^CO(1-0) and ^13^CO(1-0) observations with the IRAM 30m telescope, we analyse the small-scale structures within the two clouds. By correlating HI and far-infrared (FIR) dust continuum emission from the Planck satellite, the distribution of molecular hydrogen (H_2_) is estimated. We conduct a detailed comparison of the HI, FIR, and CO data and study variations of the XCO conversion factor. The atomic IVC does not disclose detectable CO emission. The atomic small-scale structure, as revealed by the high-resolution HI data, shows low peak HI column densities and low HI fluxes as compared to the molecular IVC. The molecular IVC exhibits a rich molecular structure and most of the CO emission is observed at the eastern edge of the cloud. There is observational evidence that the molecular IVC is in a transient and, thus, non- equilibrium phase. The average XCO factor is close to the canonical value of the Milky Way disk. We propose that the two IVCs represent different states in a gradual transition from atomic to molecular clouds. The molecular IVC appears to be more condensed allowing the formation of H_2_ and CO in shielded regions all over the cloud. Ram pressure may accumulate gas and thus facilitate the formation of H_2_. We show evidence that the atomic IVC will evolve also into a molecular IVC in a few Myr.
- ID:
- ivo://CDS.VizieR/J/AJ/154/41
- Title:
- Rotational velocities of M33
- Short Name:
- J/AJ/154/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new deep HI survey of the galaxy Messier 33 is presented, based on observations obtained at the Dominion Radio Astrophysical Observatory. We observe a perturbed outer gas distribution and kinematics in M33, and confirm the disk warping as a significant twist of the major axis of the velocity field, although no strong tilt is measured, in agreement with previous work. Evidence for a new low-brightness HI component with anomalous velocity is reported. It harbors a large velocity scatter, as its kinematics both exceeds and lags the rotation of the disk, and leaks in the forbidden velocity zone of apparent counterrotation. The observations also reveal wide and multiple-peak HI profiles that can be partly explained by crowded orbits in the framework of the warp model. Asymmetric motions are identified in the velocity field as possible signatures of a lopsided potential and the warp. The mass distribution modeling of the hybrid H{alpha}-HI rotation curve favors a cuspy dark matter halo with a concentration in disagreement with the {Lambda}CDM dark halo mass-concentration relationship. The total mass enclosed in 23kpc is 8,10^10^M_{Sun}_, of which 11% are stars and gas. At the virial radius of the cuspy halo, the resulting total mass is 5,10^11^M_{Sun}_, but with a baryonic mass fraction of only 2%. This strongly suggests a more realistic radius encompassing the total mass of M33 that is well smaller than the virial radius of the halo, possibly comparable to the size of the HI disk.
- ID:
- ivo://CDS.VizieR/J/AJ/117/2039
- Title:
- Sc galaxies I photometry, 21cm data
- Short Name:
- J/AJ/117/2039
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A compilation of 21 cm line spectral parameters specifically designed for application of the Tully-Fisher (TF) distance method is presented for 1201 spiral galaxies, primarily field Sc galaxies, for which optical I-band photometric imaging is also available. New H I line spectra have been obtained for 881 galaxies. For an additional 320 galaxies, spectra available in a digital archive have been reexamined to allow application of a single algorithm for the derivation of the TF velocity width parameter. A velocity width algorithm is used that provides a robust measurement of rotational velocity and permits an estimate of the error on that width taking into account the effects of instrumental broadening and signal-to-noise. The digital data are used to establish regression relations between measurements of velocity widths using other common prescriptions so that comparable widths can be derived through conversion of values published in the literature. The uniform H I line widths presented here provide the rotational velocity measurement to be used in deriving peculiar velocities via the TF method.
