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4071. Very young galaxies in the local Universe
ID:
ivo://CDS.VizieR/J/MNRAS/502/4815
Title:
Very young galaxies in the local Universe
Short Name:
J/MNRAS/502/4815
Date:
21 Oct 2021
Publisher:
CDS
Description:
In the local Universe, there are a handful of dwarf compact star-forming galaxies with extremely low oxygen abundances. It has been proposed that they are young, having formed a large fraction of their stellar mass during their last few hundred Myr. However, little is known about the fraction of young stellar populations in more massive galaxies. In a previous article, we analysed 404000 Sloan Digital Sky Survey spectra to identify a surprisingly large sample of more massive very young galaxies (VYGs), defined to have formed at least 50 per cent of their stellar mass within the last 1Gyr. Here, we investigate in detail the properties of a subsample of 207 galaxies that are VYGs according to all three of our spectral models. We compare their properties with those of control sample galaxies (CSGs). We find that VYGs tend to have higher surface brightness and to be more compact, dusty, asymmetric, and clumpy than CSGs. Analysis of a subsample with H I detections reveals that VYGs are more gas rich than CSGs. VYGs tend to reside more in the inner parts of low-mass groups and are twice as likely as CSGs to be interacting with a neighbour galaxy. On the other hand, VYGs and CSGs have similar gas metallicities and large-scale environments (relative to filaments and voids). These results suggest that gas-rich interactions and mergers are the main mechanisms responsible for the recent triggering of star formation in low-redshift VYGs, except for the lowest mass VYGs, where the starbursts would arise from a mixture of mergers and gas infall.
4072. VEXAS DR2 catalogs
ID:
ivo://CDS.VizieR/II/369
Title:
VEXAS DR2 catalogs
Short Name:
II/369
Date:
22 Feb 2022
Publisher:
CDS
Description:
We present the second public data release of the VISTA EXtension to Auxiliary Surveys (VEXAS DR2), where we classify objects into stars, galaxies and quasars based on an ensemble of machine learning algorithms. The aim of VEXAS is to build the widest multi-wavelength catalogue, providing reference magnitudes, colours and morphological information for a large number of scientific uses. We apply an ensemble of thirty-two different machine learning models, based on three different algorithms and on different magnitude sets, training samples and classification problems (two or three classes) on the three VEXAS Data Release 1 (DR1) optical+infrared (IR) tables. The tables were created in DR1 cross-matching VISTA near-infrared data with Wide-field Infrared Survey Explorer far-infrared data and with optical magnitudes from the Dark Energy Survey (VEXAS-DESW), the Sky Mapper Survey (VEXAS-SMW), and the Panoramic Survey Telescope and Rapid Response System Survey (VEXAS-PSW). We assemble a large table of spectroscopically confirmed objects (VEXAS-SPEC-GOOD, 415 628 unique objects), based on the combination of six different spectroscopic surveys that we use for training. We develop feature imputation to classify also objects for which magnitudes in one or more bands are missing. We classify in total 90106 objects in the Southern Hemisphere. Among these, ~62.9x10^6^ (~52.6x10^6^) are classified as 'high confidence' ('secure') stars, ~920000 (~750000) as 'high confidence' ('secure') quasars and ~34.8 (~34.1) millions as 'high confidence' ('secure') galaxies, with pclass>=0.7 (pclass>=0.9). The DR2 tables update the DR1 with the addition of imputed magnitudes and membership probabilities to each of the three classes. The density of high-confidence extragalactic objects varies strongly with the survey depth: at pclass>0.7; there are 111/deg^2^ quasars in the VEXAS-DESW footprint and 103/deg^2^ in the VEXAS-PSW footprint, while only 10.7/deg^2^ in the VEXASSM footprint. Improved depth in the midIR and coverage in the optical and nearIR are needed for the SM footprint that is not already covered by DESW and PSW.
4073. VI and [Fe/H] of Fornax dSph RGB stars
ID:
ivo://CDS.VizieR/J/A+A/459/423
Title:
VI and [Fe/H] of Fornax dSph RGB stars
Short Name:
J/A+A/459/423
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of the DART imaging and CaII triplet (CaT) survey of the Fornax dwarf spheroidal galaxy (dSph) at ESO. We collected hundreds of low resolution spectra of Red Giant Branch (RGB) stars in the CaT region, using VLT/FLAMES in Medusa mode, with the GIRAFFE spectrograph (grating LR8, resolving power R~6500). We list the results for the targets with a S/N per Angstrom >10 and an error in velocity <5km/s, because we found this to be the minimum for an accurate determination of velocity and equivalent width. We checked the sample to weed out any spurious object (e.g., broken fibres, background galaxies, foreground stars, spectra not consistent with RGBs). We use a 2.5sigma cut from the system velocity to derive which stars are probable velocity members of the Fornax dSph. We transform the equivalent width of the CaT lines of probable velocity members into metallicity ([Fe/H]) using the relation derived by Rutledge et al. (1997PASP..109..907R) and combining the CaT lines as in Tolstoy et al. (2001MNRAS.327..918T). The errors in [Fe/H] are based on S/N computations and adjusted to agree with repeated measurements.
4074. VI HST photometry of VV124 = UGC4879
ID:
ivo://CDS.VizieR/J/A+A/533/A37
Title:
VI HST photometry of VV124 = UGC4879
Short Name:
J/A+A/533/A37
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present deep V and I photometry of the isolated dwarf galaxy VV124=UGC4879, obtained from archival images taken with the Hubble Space Telescope - Advanced Camera for Surveys. In the color-magnitude diagrams of stars at distances larger than 40" from the center of the galaxy, we clearly identify for the first time a well-populated old Horizontal Branch (HB). We show that the distribution of these stars is more extended than that of Red Clump stars. This implies that very old and metal poor populations becomes more and more dominant in the outskirts of VV124. We also identify a massive (M=1.2+/-0.2x10^4^M_{sun}_) young (age=250+/-50Myr) star cluster (C1), as well as another of younger age (C2<~30+/-10Myr) with a mass similar to classical open clusters (M<=3.3+/-0.5x10^3^M_{sun}_). Both clusters lie at projected distances smaller than 100pc from the center of the galaxy.
4075. VIJsKs photometry in AM 1339-445 and AM1343-452
ID:
ivo://CDS.VizieR/J/A+A/448/983
Title:
VIJsKs photometry in AM 1339-445 and AM1343-452
Short Name:
J/A+A/448/983
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the red giant populations of two dwarf elliptical (dE) galaxies, AM 1339-445 and AM 1343-452. The galaxies are members of the Centaurus A group (D~3.8Mpc), and are classified as outlying (R~350kpc) satellites of Cen A. The analysis is based on near-IR photometry for individual red giant stars, derived from images obtained with ISAAC on the VLT, and on optical V and I photometry, derived from WFPC2 images retrieved from the HST science archive. The data enable us to investigate the stellar populations of these galaxies in the vicinity of the red giant branch (RGB) tip. In both systems we find stars above the RGB tip, which we interpret as intermediate-age upper-AGB stars. Their luminosities suggest ages of approximately 6.5+/-1 and 4+/-1Gyr as estimates for the epoch of the last episode of significant star formation in these systems. In both cases the number of upper-AGB stars suggests that ~15% of the total stellar population is in the form of intermediate-age stars.
4076. VIK photometry of faint field galaxies
ID:
ivo://CDS.VizieR/J/ApJ/475/445
Title:
VIK photometry of faint field galaxies
Short Name:
J/ApJ/475/445
Date:
21 Oct 2021
Publisher:
CDS
Description:
We combine deep K-band (W. M. Keck Telescope) with V- and I-band (New Technology Telescope) observations of two "blank" high Galactic latitude fields, surveying a total of ~2arcmin^2^. The K-band number-magnitude counts continue to rise above K~22mag, reaching surface densities of few x10^5^deg^-2^. The slope for the galaxy counts is approximately [dlog(N)/dmag].deg^-2^=0.23+/-0.02 over the range 18-23mag. While this slope is consistent with other recent deep K-band surveys, there is a definite scatter in the normalisations by about a factor of 2. In particular, our normalisation is ~2x greater than the galaxy counts reported by Djorgovski et al. in 1995 (1995ApJ...438L..13D). Optical near-infrared color-magnitude and color-color diagrams for all objects detected in the V+I+K image are plotted and discussed in the context of grids of Bruzual-Charlot isochrone synthesis galaxy evolutionary models. The colors of most of the observed galaxies are consistent with a population drawn from a broad redshift distribution. A few galaxies at K~19-20 are red in both colors (V-I>3; I-K>2, consistent with being early-type galaxies having undergone a burst of star formation at z>5 and viewed at z~1. At K>20, we find several (approximately eight) "red outlier" galaxies with I-K>4 and V-I<2.5, whose colors are difficult to mimic by a single evolving or nonevolving stellar population at any redshift unless they either have quite low metallicity or are highly reddened. We compare the data against the evolutionary tracks of second-burst ellipticals and against a grid of models that does not constrain galaxy ages to a particular formation redshift. The red outliers' surface density is several per square arcminute, which is so high that they are probably common objects of low luminosity L<L*. Whether these are low-metallicity, dusty dwarf galaxies, or old galaxies at high redshift, they are curious and merit spectroscopic follow-up.
4077. VI light curves of NGC 247 Cepheids
ID:
ivo://CDS.VizieR/J/AJ/136/1770
Title:
VI light curves of NGC 247 Cepheids
Short Name:
J/AJ/136/1770
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report on the discovery of a Cepheid population in the Sculptor Group spiral galaxy NGC 247 for the first time. On the basis of wide-field images collected in photometric surveys in V and I bands that were conducted with three different telescopes and cameras, 23 Cepheid variables were discovered with periods ranging from 17 to 131 days.
4078. VI magnitudes of NGC 4535 stars
ID:
ivo://CDS.VizieR/J/A+A/618/A185
Title:
VI magnitudes of NGC 4535 stars
Short Name:
J/A+A/618/A185
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyzed the massive star population of the Virgo Cluster galaxy NGC 4535 using archival Hubble Space Telescope Wide Field Planetary Camera 2 images in filters F555W and F814W, equivalent to Johnson V and Kron-Cousins I. We performed high precision point spread function fitting photometry of 24353 sources including 3762 candidate blue supergiants, 841 candidate yellow supergiants and 370 candidate red supergiants. We estimated the ratio of blue to red supergiants as a decreasing function of galactocentric radius. Using Modules for Experiments in Stellar Astrophysics isochrones at solar metallicity, we defined the luminosity function and estimated the star formation history of the galaxy over the last 60Myrs. We conducted a variability search in the V and I filters using three variability indexes: the median absolute deviation, the interquartile range and the inverse von-Neumann ratio. This analysis yielded 120 new variable candidates with absolute magnitudes ranging from M_V_=-4 to -11mag. We used the MESA evolutionary tracks at solar metallicity, to classify the variables based on their absolute magnitude and their position on the color-magnitude diagram. Among the new candidate variable sources are eight candidate variable red supergiants, three candidate variable yellow supergiants and one candidate luminous blue variable, which we suggest for follow-up observations.
4079. VIMOS Public Extragalactic Survey (VIPERS) DR1
ID:
ivo://CDS.VizieR/J/A+A/562/A23
Title:
VIMOS Public Extragalactic Survey (VIPERS) DR1
Short Name:
J/A+A/562/A23
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first Public Data Release (PDR-1) of the VIMOS Public Extragalactic Survey (VIPERS). It comprises 57204 spectroscopic measurements together with all additional information necessary for optimal scientific exploitation of the data, in particular the associated photometric measurements and quantification of the photometric and survey completeness. VIPERS is an ESO Large Programme designed to build a spectroscopic sample of =~100000 galaxies with i_AB_<22.5 and 0.5<z<1.2 with high sampling rate (=~45%). The survey spectroscopic targets are selected from the CFHTLS-Wide five-band catalogues in the W1 and W4 fields. The final survey will cover a total area of nearly 24 deg^2^, for a total comoving volume between z=0.5 and 1.2 of =~4x10^7^(Mpc/h)^3^ and a median galaxy redshift of z=~0.8. The release presented in this paper includes data from virtually the entire W4 field and nearly half of the W1 area, thus representing 64% of the final dataset. We provide a detailed description of sample selection, observations and data reduction procedures; we summarise the global properties of the spectroscopic catalogue and explain the associated data products and their use, and provide all the details for accessing the data through the survey database (http://vipers.inaf.it) where all information can be queried interactively.
4080. VIMOS Ultra Deep Survey (VUDS) DR1
ID:
ivo://CDS.VizieR/J/A+A/600/A110
Title:
VIMOS Ultra Deep Survey (VUDS) DR1
Short Name:
J/A+A/600/A110
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper describes the first data release (DR1) of the VIMOS Ultra Deep Survey (VUDS). The VUDS-DR1 is the release of all low-resolution spectroscopic data obtained in 276.9 arcmin^2^ of the CANDELS-COSMOS and CANDELS-ECDFS survey areas, including accurate spectroscopic redshifts z_spec_ and individual spectra obtained with VIMOS on the ESO-VLT. A total of 698 objects have a measured redshift, with 677 galaxies, two type-I AGN, and a small number of 19 contaminating stars. The targets of the spectroscopic survey are selected primarily on the basis of their photometric redshifts to ensure a broad population coverage. About 500 galaxies have z_spec_>2, 48of which have z_spec_>4; the highest reliable redshifts reach beyond z_spec_=6. This data set approximately doubles the number of galaxies with spectroscopic redshifts at z>3 in these fields. We discuss the general properties of the VUDS-DR1 sample in terms of the spectroscopic redshift distribution, the distribution of Lyman-{alpha} equivalent widths, and physical properties including stellar masses M* and star formation rates derived from spectral energy distribution fitting with the knowledge of z_spec_. We highlight the properties of the most massive star-forming galaxies, noting the wide range in spectral properties, with Lyman-{alpha} in emission or in absorption, and in imaging properties with compact, multi-component, or pair morphologies. We present the catalogue database and data products. All VUDS-DR1 data are publicly available and can be retrieved from a dedicated query-based database. Future VUDS data releases will follow this VUDS-DR1 to give access to the spectra and associated measurement of ~8000 objects in the full ~1 square degree of the VUDS survey.