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16851. Very thin discs galaxies properties
ID:
ivo://CDS.VizieR/J/MNRAS/465/3784
Title:
Very thin discs galaxies properties
Short Name:
J/MNRAS/465/3784
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the properties of galaxies with very thin discs (VTDs) using a sample of 85 objects whose stellar disc radial-to-vertical scale ratio determined from photometric decomposition, exceeds 9. We present evidences of similarities between the VTD galaxies and low surface brightness (LSB) disc galaxies, and conclude that both small and giant LSB galaxies may reveal themselves as VTD, edge-on galaxies. Our VTD galaxies are mostly bulgeless, and those with large radial scalelength tend to have redder colours. We performed spectral observations of 22 VTD galaxies with the Dual Imaging Spectrograph on the 3.5 m telescope at the Apache Point Observatory. The spectra with good resolution (R~5000) allow us to determine the distance and the ionized gas rotation curve maximum for the galaxies. Our VTD galaxies have low dust content, in contrast to regular disc galaxies. Apparently, VTD galaxies reside in specific cosmological low-density environments and tend to have less connection with filaments. Comparing a toy model that assumes marginally low star formation in galactic discs with obtained gas kinematics data, we conclude that there is a threshold central surface density of about 88M_{sun}_/pc^2^, which we observe in the case of very thin, rotationally supported galactic discs.
16852. Very young galaxies from SDSS
ID:
ivo://CDS.VizieR/J/MNRAS/492/1791
Title:
Very young galaxies from SDSS
Short Name:
J/MNRAS/492/1791
Date:
21 Oct 2021
Publisher:
CDS
Description:
Only a handful of galaxies in the local Universe appear to be very young. We estimate the fraction of very young galaxies (VYGs), defined as those with more than half their stellar masses formed within the last Gyr. We fit non-parametric star formation histories (SFHs) to ~280000 galaxy spectra from a flux- and volume-limited subsample of the Main Galaxy Sample (MGS) of the SDSS, which is also complete in mass-to-light ratio, thus properly accounting for passive galaxies of a given mass. The VYG fractions decrease with increasing galaxy stellar mass, from ~50 per cent at m=10^8^M_{sun}_ to ~0.1 per cent at m=10^11.5^M_{sun}_, with differences of up to 1dex between the different spectral models used to estimate the SFH and on how we treat aperture effects. But old stellar populations may hide in our VYGs despite our conservative VYG sample built with galaxies that are globally bluer than within the region viewed by the SDSS fibre. The VYG fractions versus mass decrease more gradually compared to the Tweed et al. (2018MNRAS.477.1427T) predictions using analytical and semi-analytical models of galaxy formation, but agree better with the SIMBA hydrodynamical simulation. These discrepancies highlight the usefulness of VYGs in constraining the strong uncertainties in both galaxy formation models and spectral modelling of galaxy SFHs. Given the lognormal cosmic SFH, these mean VYG fractions suggest that galaxies above 10^8^M_{sun}_ undergo at most four major starbursts on average.
16853. 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.
16854. 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.
16855. VFTS. B-type stars classification and RV
ID:
ivo://CDS.VizieR/J/A+A/574/A13
Title:
VFTS. B-type stars classification and RV
Short Name:
J/A+A/574/A13
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present spectral classifications for 438 B-type stars observed as part of the VLT-FLAMES Tarantula Survey (VFTS) in the 30 Doradus region of the Large Magellanic Cloud. Radial velocities are provided for 307 apparently single stars, and for 99 targets with radial-velocity variations which are consistent with them being spectroscopic binaries. We investigate the spatial distribution of the radial velocities across the 30 Dor region, and use the results to identify candidate runaway stars. Excluding potential runaways and members of two older clusters in the survey region (SL639 and Hodge301), we determine a systemic velocity for 30 Dor of 271.6+/-12.2km/s from 273 presumed single stars. Employing a 3{sigma} criterion we identify nine candidate runaway stars (2.9% of the single stars with radial-velocity estimates). The projected rotational velocities of the candidate runaways appear to be significantly different to those of the full B-type sample, with a strong preference for either large (>=345km/s) or small (<=65km/s) rotational velocities. Of the candidate runaways, VFTS358 (classified B0.5: V) has the largest differential radial velocity (-106.9+/-16.2km/s), and a preliminary atmospheric analysis finds a significantly enriched nitrogen abundance of 12+log(N/H)> 8.5. Combined with a large rotational velocity (v_e_sini=345+/-22km/s), this is suggestive of past binary interaction for this star.
16856. VFTS. O-type stellar content of 30 Dor
ID:
ivo://CDS.VizieR/J/A+A/564/A40
Title:
VFTS. O-type stellar content of 30 Dor
Short Name:
J/A+A/564/A40
Date:
21 Oct 2021
Publisher:
CDS
Description:
Detailed spectral classifications are presented for 352 O-B0 stars in the VLT-FLAMES Tarantula Survey ESO Large Programme, of which 213 O-type are judged of sufficiently high quality for further morphological analysis. Among them, six subcategories of special interest are distinguished. (1) Several new examples of the earliest spectral types O2-O3 have been found, while a previously known example has been determined to belong to the nitrogen-rich ON2 class. (2) A group of extremely rapidly rotating main-sequence objects has been isolated, including the largest vsini values known, the spatial and radial-velocity distributions of which suggest ejection from the two principal ionizing clusters NGC 2070 and NGC 2060. (3) Several new examples of the evolved, rapidly rotating Onfp class show similar evidence, although at least some of them are spectroscopic binaries. (4) No fewer than 48 members of the Vz category, hypothesized to be on or near the zero-age main sequence, are found in this sample; in contrast to the rapid rotators, they are strongly concentrated to the ionizing clusters and a newly recognized region of current and recent star formation to the north, supporting their interpretation as very young objects, as do their relatively faint absolute magnitudes. (5) A surprisingly large fraction of the main-sequence spectra belong to the recently recognized V((fc)) class, with CIII emission lines of similar strength to the usual NIII in V((f)) spectra, although a comparable number of the latter are also present, as well as six objects with very high-quality data but no trace of either emission feature, presenting new challenges to physical interpretations. (6) Two mid-O Vz and three late-O giant/supergiant spectra with morphologically enhanced nitrogen lines have been detected. Absolute visual magnitudes have been derived for each star with individual extinction laws, and composite Hertzsprung-Russell diagrams provide evidence of the multiple generations present in this field. Spectroscopic binaries, resolved visual multiples, and possible associations with X-ray sources are noted. Astrophysical and dynamical analyses of this unique dataset underway will provide new insights into the evolution of massive stars and starburst clusters.
16857. VFTS. OVz stars in 30 Dor
ID:
ivo://CDS.VizieR/J/A+A/564/A39
Title:
VFTS. OVz stars in 30 Dor
Short Name:
J/A+A/564/A39
Date:
21 Oct 2021
Publisher:
CDS
Description:
OVz stars, a subclass of O-type dwarfs characterized by having HeII{lambda}4686 stronger in absorption than any other helium line in their blue-violet spectra, have been suggested to be on or near the zero-age main sequence (ZAMS). If their youth were confirmed, they would be key objects with which to advance our knowledge of the physical properties of massive stars in the early stages of their lives. We test the hypothesis of OVz stars being at a different (younger) evolutionary stage than are normal O-type dwarfs. We have performed the first comprehensive quantitative spectroscopic analysis of a statistically meaningful sample of OVz and OV stars in the same star-forming region, exploiting the large number of OVz stars identified by the VLT-FLAMES Tarantula Survey in the 30 Doradus region of the Large Magellanic Cloud (LMC). We obtained the stellar and wind parameters of 38 OVz stars (and a control sample of 46 OV stars) using the FASTWIND stellar atmosphere code and the IACOB-GBAT, a grid-based tool developed for automated quantitative analysis of optical spectra of O stars. In the framework of a differential study, we compared the physical and evolutionary properties of both samples, locating the stars in the logg vs. logT_eff_, logQ vs. logT_eff_, and logL/L_{sun}_ vs. logT_eff_ diagrams. We also investigated the predictions of the FASTWIND code regarding the OVz phenomenon.
16858. VGCF detection of galaxy systems
ID:
ivo://CDS.VizieR/J/A+A/444/685
Title:
VGCF detection of galaxy systems
Short Name:
J/A+A/444/685
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalog of the 48 Voronoi Galaxy Cluster Finder (VGCF) cluster detections. We provide a cluster ID, signal to noise ratios (SNR) in the B, V, R and I bands, positions, angular radius of the cluster, photometric redshift estimates (derived from color-magnitude diagrams (CMD)) and PDCS redshift estimate (Postman et al., 1996AJ....111..615P), if available. Table 5 contains cluster detections in F0028+0515, F0027+0555, F0228+0115 and F0226+0026 fields and other two regions that overlap PDCS 0h and 2h fields.
16859. VHS DR4 - VISTA Hemisphere Survey Data Release 4
ID:
ivo://wfau.roe.ac.uk/vhsDR4-dsa
Title:
VHS DR4 - VISTA Hemisphere Survey Data Release 4
Date:
23 Jan 2024 09:46:50
Publisher:
WFAU, Institute for Astronomy, University of Edinburgh
Description:
The VHS will image the entire ~20 000 square degrees of the Southern Sky, with the exception of the areas already covered by the VIKING and VVV surveys, in J and Ks. The resulting data will be about 4 magnitudes deeper than 2MASS and DENIS. The 5000 square degrees covered by the Dark Energy Survey (DES), another imaging survey scheduled to begin in 2010 at the CTIO 4 metre Blanco telescope, will also be observed in H-band. The area around both of the Galactic Caps will be observed in Y- and H- band as well to be combined with the data from the VST ATLAS survey. The main science drivers of the VHS include: examining low mass and nearby stars, studying the merger history of the Galaxy, measuring the properties of Dark Energy through the examination of large-scale structure to a redshift of ~1, and searches for high redshift quasars.
16860. VHS DR3 - VISTA Hemisphere Survey Data Release 3
ID:
ivo://wfau.roe.ac.uk/vhsDR3-dsa
Title:
VHS DR3 - VISTA Hemisphere Survey Data Release 3
Short Name:
VHS DR3
Date:
04 Dec 2019 13:40:01
Publisher:
WFAU, Institute for Astronomy, University of Edinburgh
Description:
The VHS will image the entire ~20 000 square degrees of the Southern Sky, with the exception of the areas already covered by the VIKING and VVV surveys, in J and Ks. The resulting data will be about 4 magnitudes deeper than 2MASS and DENIS. The 5000 square degrees covered by the Dark Energy Survey (DES), another imaging survey scheduled to begin in 2010 at the CTIO 4 metre Blanco telescope, will also be observed in H-band. The area around both of the Galactic Caps will be observed in Y- and H- band as well to be combined with the data from the VST ATLAS survey. The main science drivers of the VHS include: examining low mass and nearby stars, studying the merger history of the Galaxy, measuring the properties of Dark Energy through the examination of large-scale structure to a redshift of ~1, and searches for high redshift quasars.

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