- ID:
- ivo://CDS.VizieR/J/A+A/486/697
- Title:
- Hydra I Cluster Catalogue (HCC)
- Short Name:
- J/A+A/486/697
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyse the properties of the early-type dwarf galaxy population in the Hydra I cluster. We investigate the galaxy luminosity function, the colour-magnitude relation, and the magnitude-surface brightness relation down to M_V_=-10mag. Deep VLT/FORS1 images in V and I bands were examined. We identify cluster members by radial velocity measurements and select other cluster galaxy candidates by their morphology. The candidates' total magnitudes and central surface brightnesses were derived from the analysis of their surface brightness profiles.
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- ID:
- ivo://CDS.VizieR/J/A+A/659/A92
- Title:
- HydraI galaxy cluster dwarf catalog (HCDC)
- Short Name:
- J/A+A/659/A92
- Date:
- 10 Mar 2022 07:25:32
- Publisher:
- CDS
- Description:
- Due to their relatively low stellar mass content and diffuse nature, the evolution of dwarf galaxies can be strongly affected by their environment. Analyzing the properties of the dwarf galaxies over a wide range of luminosities, sizes, morphological types, and environments, we can obtain insights about their evolution. At ~50Mpc, the Hydra I cluster of galaxies is among the closest cluster in the z=~0 Universe, and an ideal environment to study dwarf galaxy properties in a cluster environment. We exploit deep imaging data of the Hydra I cluster to construct a new photometric catalog of dwarf galaxies in the cluster core, which is then used to derive properties of the Hydra I cluster dwarf galaxy population as well as to compare it with other clusters. Moreover, we investigate the dependency of dwarf galaxy properties on their surrounding environment. The new wide-field g- and r-band images of the Hydra I cluster obtained with the OmegaCAM camera on the VLT Survey Telescope (VST) in the context of the VST Early-type GAlaxy Survey (VEGAS) were used to study the dwarf galaxy population in the Hydra I cluster core down to r-band magnitude Mr=-11.5mag. We used an automatic detection tool to identify dwarf galaxies from a ~1deg^2^ field centered on the Hydra I core, covering almost half of the cluster virial radius. The photometric pipeline was used to estimate the principal photometric parameters for all targets. Scaling relations and visual inspection were used to assess the cluster membership and construct a new dwarf galaxy catalog. Finally, based on the new catalog, we studied the structural (Sersic index n, effective radius Re, and axis ratio) and photometric (colors and surface brightness) properties of the dwarf galaxies, also investigating how they vary as a function of clustercentric distance. The new Hydra I dwarf catalog contains 317 galaxies with a luminosity between -18.5<Mr<-11.5mag, a semi-major axis larger than ~200pc (a=0.84"), of which 202 are new detections, and previously unknown dwarf galaxies in the Hydra I central region. We estimate that our detection efficiency reaches 50% at the limiting magnitude Mr=-11.5mag, and at the mean effective surface brightness <{mu}_e,r_=26.5mag/arcsec^2^. We present the standard scaling relations for dwarf galaxies, which are color-magnitude, size-luminosity, and Sersic n-magnitude relations, and compare them with other nearby clusters. We find that there are no observational differences for dwarfs scaling relations in clusters of different sizes. We study the spatial distribution of galaxies, finding evidence for the presence of substructures within half the virial radius. We also find that mid- and high-luminosity dwarfs (Mr<-14.5mag) become, on average, redder toward the cluster center, and that they have a mild increase in Re with increasing clustercentric distance, similar to what is observed for the Fornax cluster. No clear clustercentric trends are reported for surface brightness and Sersic index. Considering galaxies in the same magnitude bins, we find that for high and mid-luminosity dwarfs (Mr<-13.5mag), the g-r color is redder for the brighter surface brightness and higher Sersic n index objects. This finding is consistent with the effects of harassment and/or partial gas stripping.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/39
- Title:
- Hydra I wide-field imaging and spectroscopy obs.
- Short Name:
- J/ApJ/818/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Eastern Banded Structure (EBS) and Hydra I halo overdensities are very nearby (d~10kpc) objects discovered in Sloan Digital Sky Survey (SDSS) data. Previous studies of the region have shown that EBS and Hydra I are spatially coincident, cold structures at the same distance, suggesting that Hydra I may be the EBS's progenitor. We combine new wide-field Dark Energy Camera (DECam) imaging and MMT/Hectochelle spectroscopic observations of Hydra I with SDSS archival spectroscopic observations to quantify Hydra I's present-day chemodynamical properties, and to infer whether it originated as a star cluster or dwarf galaxy. While previous work using shallow SDSS imaging assumed a standard old, metal-poor stellar population, our deeper DECam imaging reveals that Hydra I has a thin, well-defined main sequence turnoff of intermediate age (~5-6Gyr) and metallicity ([Fe/H]=-0.9dex). We measure statistically significant spreads in both the iron and alpha-element abundances of {sigma}_[Fe/H]_=0.13+/-0.02dex and {sigma}_[{alpha}/Fe]_=0.09+/-0.03dex, respectively, and place upper limits on both the rotation and its proper motion. Hydra I's intermediate age and [Fe/H] --as well as its low [{alpha}/Fe], apparent [Fe/H] spread, and present-day low luminosity-- suggest that its progenitor was a dwarf galaxy, which has subsequently lost more than 99.99% of its stellar mass.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A2
- Title:
- Hydrogen in diffuse molecular clouds
- Short Name:
- J/A+A/600/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent sub-millimeter and far-infrared wavelength observations of absorption in the rotational ground state lines of various simple molecules against distant Galactic continuum sources have opened the possibility to study the chemistry of diffuse molecular clouds Milky Way-wide. In order to calculate abundances the column densities of molecular and atomic hydrogen, HI, must be known. We aim at determining the atomic hydrogen column densities for diffuse clouds located on the sight lines toward a sample of prominent high mass star forming regions that were intensely studied with the HIFI instrument onboard Herschel. Based on Jansky Very Large Array data, we employ the 21-cm HI absorption-line technique to construct profiles of the HI opacity versus radial velocity toward our target sources. These profiles are combined with lower resolution archival data of extended HI emission to calculate the HI column densities of the individual clouds along the sight lines. We employ Bayesian inference to estimate the uncertainties of the derived quantities. Our study delivers reliable estimates of the atomic hydrogen column density for a large number of diffuse molecular clouds at various Galactocentric distances. Together with column densities of molecular hydrogen derived from its surrogates observed with HIFI, the measurements can be used to characterize the clouds and, e.g., investigate the dependence of their chemistry on the molecular fraction.
- ID:
- ivo://CDS.VizieR/II/40
- Title:
- Hydrogen-Line Absorption in Early-Type Stars
- Short Name:
- II/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric determinations of H-{gamma} absorption line intensity have been made of stars in selected clusters and associations as well as in the general galactic field. Interference filters having a width at half intensity of 45{AA} were used to isolate spectral regions centered on 4280{AA}, H-{gamma} and 4410{AA}. The {Gamma} indices derived, which represent a measure of H-{gamma} absorption, can be used in conjunction with unreddened values of either (U-B) or (B-V) for spectral and luminosity class determinations of stars in the spectral range O6 to A0.
- ID:
- ivo://CDS.VizieR/J/ApJ/810/42
- Title:
- Hydrogen RRL parameters of H II regions
- Short Name:
- J/ApJ/810/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- H II regions are the ionized spheres surrounding high-mass stars. They are ideal targets for tracing Galactic structure because they are predominantly found in spiral arms and have high luminosities at infrared and radio wavelengths. In the Green Bank Telescope H II Region Discovery Survey (GBT HRDS), we found that >30% of first Galactic quadrant H II regions have multiple hydrogen radio recombination line (RRL) velocities, which makes determining their Galactic locations and physical properties impossible. Here we make additional GBT RRL observations to determine the discrete H II region velocity for all 117 multiple-velocity sources within 18{deg}<l<65{deg}. The multiple-velocity sources are concentrated in the zone 22{deg}<l<32{deg}, coinciding with the largest regions of massive star formation, which implies that the diffuse emission is caused by leaked ionizing photons. We combine our observations with analyses of the electron temperature, molecular gas, and carbon recombination lines to determine the source velocities for 103 discrete H II regions (88% of the sample). With the source velocities known, we resolve the kinematic distance ambiguity for 47 regions, and thus determine their heliocentric distances.
- ID:
- ivo://CDS.VizieR/J/MNRAS/428/3355
- Title:
- Hydrogen volume densities in nearby galaxies
- Short Name:
- J/MNRAS/428/3355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a simple model of photodissociated atomic hydrogen on a galactic scale, it is possible to derive total hydrogen volume densities. These densities, obtained through a combination of atomic hydrogen, far-ultraviolet and metallicity data, provide an independent probe of the combined atomic and molecular hydrogen gas in galactic discs. We present a new, flexible and fully automated procedure using this simple model. This automated method will allow us to take full advantage of a host of available data on galaxies in order to calculate the total hydrogen volume densities of the giant molecular clouds surrounding sites of recent star formation. Until now this was only possible on a galaxy-by-galaxy basis using by-eye analysis of candidate photodissociation regions. We test the automated method by adopting various models for the dust-to-gas ratio and comparing the resulting densities for M74, including a new metallicity map of M74 produced by integral field spectroscopy. We test the procedure against previously published M83 volume densities based on the same method and find no significant differences. The range of total hydrogen volume densities obtained for M74 is approximately 5-700cm^-3^. Different dust-to-gas ratio models do not result in measurably different densities. The cloud densities presented here mean that M74 is added to the list of galaxies analysed using the assumption of photodissociated atomic hydrogen occurring near sites of recent star formation, and consolidate the method. For the first time, full metallicity maps are included in the analysis as opposed to metallicity gradients. The results will need to be compared with other tracers of the interstellar medium and photodissociation regions, such as CO and CII, in order to test our basic assumptions, specifically our assumption that the HI we detect originates in photodissociation regions.
6718. Hypercompact HII regions
- ID:
- ivo://CDS.VizieR/J/A+A/645/A110
- Title:
- Hypercompact HII regions
- Short Name:
- J/A+A/645/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The derived physical parameters for young HII regions are normally determined assuming the emission region to be optically-thin. However, this is unlikely to hold for young HII regions such as Hyper-compact HII(HCHII) and Ultra-compact HII(UCHII) regions and leads to the underestimation of their properties. This can be overcome by fitting the SEDs over a wide range of radio frequencies. Two primary goals are (1) determining physical properties from radio SEDs and finding potential HCHII regions; (2) using these physical properties to investigate their evolution. We used Karl G. Jansky Very Large Array (VLA) to make observations of X-band and K-band with angular-resolutions of ~1.7" and ~0.7", respectively, toward 114 HII regions with rising-spectra between 1-5GHz. We complement our observations with VLA archival data and construct SEDs between 1-26GHz and model them assuming an ionisation-bounded HII region with uniform density. The sample has a mean electron density of ne=1.6*10^4^cm^-3^, diameter diam=0.14pc, and emission measure EM=1.9*10^7^pc/cm^6^. We identify 16 HCHII region candidates and 8 intermediate objects between the classes of HCHII and UCHII regions. The ne, diam, and EM change as expected, however, the Lyman continuum flux is relatively constant over time. We find that about 67% of Lyman continuum photons are absorbed by dust within these HII regions and the dust absorption fraction tends to be more significant for more compact and younger HII regions. Young HII regions are commonly located in dusty clumps; HCHII regions and intermediate objects are often associated with various masers, outflows, broad radio recombination lines, and extended green objects, and the accretion at the two stages tends to be quickly reduced or halted.
- ID:
- ivo://CDS.VizieR/VII/237
- Title:
- HYPERLEDA. I. Catalog of galaxies
- Short Name:
- VII/237
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the new catalog of principal galaxies (PGC2003). It constitutes the framework of the HYPERLEDA database that supersedes the LEDA one, with more data and more capabilities. The catalog is still restricted to confirmed galaxies, i.e. about one million galaxies, brighter than ~18B-mag. In order to provide the best possible identification for each galaxy we give: accurate coordinates (typical accuracy better than 2 arcsec), diameter, axis ratio and position angle. Diameters and axis ratios have been homogenized to the RC2 system at the limiting surface brightness of 25B-mag/arcsec^2^, using a new method, the EPIDEMIC method. In order to provide the best designation for each galaxy, we collected the names from 50 catalogues. The compatibility of the spelling is tested against NED and SIMBAD, and, as far as possible we used a spelling compatible with both. For some cases, where no consensus exists between NED, SIMBAD and LEDA, we propose some changes that could make the spelling of names fully compatible. The full catalog is distributed through the CDS and can be extracted from HYPERLEDA, http://leda.univ-lyon1.fr/ .
- ID:
- ivo://CDS.VizieR/VII/238
- Title:
- HYPERLEDA. II. Homogenized HI data
- Short Name:
- VII/238
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- After a compilation of HI data from 611 references and new observations made in Nancay, we produce a catalog of homogenized HI data for 16781 galaxies. The homogenization is made using the EPIDEMIC method from which all data are progressively converted into the adopted standard. The result is a catalog giving: 1) the logarithm of twice the maximum rotation velocity, log2V_M_^sini^, converted to the system of Mathewson et al. (1996ApJS..107...97M). This quantity is given without correction for inclination; 2) the HI magnitude, m_21_, (area of the 21-cm line width expressed in magnitude) converted to the flux system of Theureau et al. (1998A&AS..130..333T); 3) the HI velocity, V_HI_, expressed with the optical definition (i.e., using wavelengths instead frequencies). The typical uncertainties are: 0.04 for log2V_M_^sini^, 0.25mag for m_21_ and 9km/s for V_HI_.