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631. Ages of star clusters in SMC
ID:
ivo://CDS.VizieR/J/ApJ/853/104
Title:
Ages of star clusters in SMC
Short Name:
J/ApJ/853/104
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new study of the spatial distribution and ages of the star clusters in the Small Magellanic Cloud (SMC). To detect and estimate the ages of the star clusters we rely on the new fully automated method developed by Bitsakis+ (2017, J/ApJ/845/56). Our code detects 1319 star clusters in the central 18deg^2^ of the SMC we surveyed (1108 of which have never been reported before). The age distribution of those clusters suggests enhanced cluster formation around 240Myr ago. It also implies significant differences in the cluster distribution of the bar with respect to the rest of the galaxy, with the younger clusters being predominantly located in the bar. Having used the same setup, and data from the same surveys as for our previous study of the LMC, we are able to robustly compare the cluster properties between the two galaxies. Our results suggest that the bulk of the clusters in both galaxies were formed approximately 300Myr ago, probably during a direct collision between the two galaxies. On the other hand, the locations of the young (<=50Myr) clusters in both Magellanic Clouds, found where their bars join the HI arms, suggest that cluster formation in those regions is a result of internal dynamical processes. Finally, we discuss the potential causes of the apparent outside-in quenching of cluster formation that we observe in the SMC. Our findings are consistent with an evolutionary scheme where the interactions between the Magellanic Clouds constitute the major mechanism driving their overall evolution.
632. Ages of star clusters in tidal tails of 3 galaxies
ID:
ivo://CDS.VizieR/J/ApJ/805/99
Title:
Ages of star clusters in tidal tails of 3 galaxies
Short Name:
J/ApJ/805/99
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the stellar content in the tidal tails of three nearby merging galaxies, NGC 520, NGC 2623, and NGC 3256, using BVI imaging taken with the Advanced Camera for Surveys on board the Hubble Space Telescope (HST). The tidal tails in all three systems contain compact and fairly massive young star clusters, embedded in a sea of diffuse, unresolved stellar light. We compare the measured colors and luminosities with predictions from population synthesis models to estimate cluster ages and find that clusters began forming in tidal tails during or shortly after the formation of the tails themselves. We find a lack of very young clusters (<=10Myr old), implying that eventually star formation shuts off in the tails as the gas is used up or dispersed. There are a few clusters in each tail with estimated ages that are older than the modeled tails themselves, suggesting that these may have been stripped out from the original galaxy disks. The luminosity function of the tail clusters can be described by a single power-law, dN/dL{propto}L^{alpha}^, with -2.6<{alpha}<-2.0. We find a stellar age gradient across some of the tidal tails, which we interpret as a superposition of (1) newly formed stars and clusters along the dense center of the tail and (2) a sea of broadly distributed, older stellar material ejected from the progenitor galaxies.
633. Ages of stars in dwarf galaxies
ID:
ivo://CDS.VizieR/J/MNRAS/412/1539
Title:
Ages of stars in dwarf galaxies
Short Name:
J/MNRAS/412/1539
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the variation of spatial structure of stellar populations within dwarf galaxies as a function of the population age. We use deep Hubble Space Telescope/Advanced Camera for Surveys imaging of nearby dwarf galaxies in order to resolve individual stars and create composite colour-magnitude diagrams (CMDs) for each galaxy. Using the obtained CMDs, we select blue helium burning stars, which can be unambiguously age-dated by comparing the absolute magnitude of individual stars with stellar isochrones. Additionally, we select a very young (~<10Myr) population of OB stars for a subset of the galaxies based on the tip of the young main sequence. By selecting stars in different age ranges, we can then study how the spatial distribution of these stars evolves with time.
634. Ages of the planet host stars
ID:
ivo://CDS.VizieR/J/A+A/649/A111
Title:
Ages of the planet host stars
Short Name:
J/A+A/649/A111
Date:
22 Feb 2022
Publisher:
CDS
Description:
Revealing the mechanisms shaping the architecture of planetary systems is crucial for our understanding of their formation and evolution. In this context, it has been recently proposed that stellar clustering might be the key in shaping the orbital architecture of exoplanets. The main goal of this work is to explore the factors that shape the orbits of planets. We performed different statistical tests to compare the properties of planets and their host stars associated with different stellar environments. Results. We used a homogeneous sample of relatively young FGK dwarf stars with radial velocity detected planets and tested the hypothesis that their association to phase space (position-velocity) over-densities ("cluster" stars) and under-densities ("field" stars) impacts the orbital periods of planets. When controlling for the host star properties on a sample of 52 planets orbiting around cluster stars and 15 planets orbiting around field stars, we found no significant difference in the period distribution of planets orbiting these two populations of stars. By considering an extended sample of 73 planets orbiting around cluster stars and 25 planets orbiting field stars, a significant difference in the planetary period distributions emerged. However, the hosts associated with stellar under-densities appeared to be significantly older than their cluster counterparts. This does not allow us to conclude as to whether the planetary architecture is related to age, environment, or both. We further studied a sample of planets orbiting cluster stars to study the mechanism responsible for the shaping of orbits of planets in similar environments. We could not identify a parameter that can unambiguously be responsible for the orbital architecture of massive planets, perhaps, indicating the complexity of the issue. An increased number of planets in clusters and in over-density environments will help to build large and unbiased samples which will then allow to better understand the dominant processes shaping the orbits of planets.
635. AGES sources in Virgo cluster
ID:
ivo://CDS.VizieR/J/MNRAS/423/787
Title:
AGES sources in Virgo cluster
Short Name:
J/MNRAS/423/787
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present 21-cm observations of a 10x2deg^2^ region in the Virgo cluster, obtained as part of the Arecibo Galaxy Environment Survey. 289 sources are detected over the full redshift range (-2000<Vhel<+20000km/s) with 95 belonging to the cluster (Vhel<3000km/s). We combine our observations with data from the optically selected Virgo Cluster Catalogue (VCC) and the Sloan Digital Sky Survey. Most of our detections can be clearly associated with a unique optical counterpart, and 30 per cent of the cluster detections are new objects fainter than the VCC optical completeness limit. Seven detections may have no optical counterpart and we discuss the possible origins of these objects. Seven detections appear associated with early-type galaxies. We perform HI stacking on the HI-undetected galaxies listed in the VCC in this region and show that they must have significantly less gas than those actually detected in HI. Galaxies undetected in HI in the cluster appear to be really devoid of gas, in contrast to a sample of field galaxies from the Arecibo Legacy Fast ALFA (ALFALFA).
636. AGES: the AGN and Galaxy Evolution Survey
ID:
ivo://CDS.VizieR/J/ApJS/200/8
Title:
AGES: the AGN and Galaxy Evolution Survey
Short Name:
J/ApJS/200/8
Date:
21 Oct 2021
Publisher:
CDS
Description:
The AGN and Galaxy Evolution Survey (AGES) is a redshift survey covering, in its standard fields, 7.7deg^2^ of the Bootes field of the NOAO Deep Wide-Field Survey. The final sample consists of 23745 redshifts. There are well-defined galaxy samples in 10 bands (the B_W_, R, I, J, K, IRAC 3.6, 4.5, 5.8, and 8.0um, and MIPS 24um bands) to a limiting magnitude of I<20mag for spectroscopy. For these galaxies, we obtained 18163 redshifts from a sample of 35200 galaxies, where random sparse sampling was used to define statistically complete sub-samples in all 10 photometric bands. The median galaxy redshift is 0.31, and 90% of the redshifts are in the range 0.085<z<0.66. Active galactic nuclei (AGNs) were selected as radio, X-ray, IRAC mid-IR, and MIPS 24um sources to fainter limiting magnitudes (I<22.5mag for point sources). Redshifts were obtained for 4764 quasars and galaxies with AGN signatures, with 2926, 1718, 605, 119, and 13 above redshifts of 0.5, 1, 2, 3, and 4, respectively. We detail all the AGES selection procedures and present the complete spectroscopic redshift catalogs and spectral energy distribution decompositions. Photometric redshift estimates are provided for all sources in the AGES samples.
637. AGESVC1 282 deep optical image
ID:
ivo://CDS.VizieR/J/A+A/642/L10
Title:
AGESVC1 282 deep optical image
Short Name:
J/A+A/642/L10
Date:
21 Oct 2021
Publisher:
CDS
Description:
The blind HI survey Arecibo Galaxy Environment Survey (AGES) detected several unresolved sources in the Virgo cluster, which do not have optical counterparts in the Sloan Digital Sky Survey. The origin of these dark clouds is unknown. They might be crucial objects since they could be the so-called dark galaxies, that is, the dark matter halos without stellar content that are expected from cosmological simulations. In order to reveal the nature of the dark clouds, we took a deep optical image of one them, AGESVC1 282, with the newly-commissioned 1.4m Milankovic Telescope. After observing it for 10.4h in the L-filter, the image reached a surface-brightness limit of about 29.1mag/arcsec^+2^ in V. No optical counterpart was detected. We placed an upper limit on the Vband luminosity of the object of 1.1x10^7^L_{sun}_, giving a stellar mass below 1.4x10^7^M_{sun}_ and a HI-to-stellar mass ratio above 3.1. By inspecting archival HI observations of the surrounding region, we found that none of the standard explanations for optically dark HI clouds fits the available constraints on this object.
638. Age & [Z/H] relations of SDSS star-forming galaxies
ID:
ivo://CDS.VizieR/J/ApJ/898/62
Title:
Age & [Z/H] relations of SDSS star-forming galaxies
Short Name:
J/ApJ/898/62
Date:
13 Dec 2021 08:21:08
Publisher:
CDS
Description:
Stellar population parameters correlate with a range of galaxy properties, but it is unclear which relations are causal and which are the result of another underlying trend. In this series, we quantitatively compare trends between stellar population properties and galaxy structural parameters in order to determine which relations are intrinsically tighter, and are therefore more likely to reflect a causal relation. Specifically, we focus on the galaxy structural parameters of mass M, gravitational potential {Phi}~M/R_e_, and surface mass density {Sigma}~M/R_e_^2^. In Barone+ (Paper I; 2018ApJ...856...64B) we found that for early-type galaxies (ETGs) the age-{Sigma} and [Z/H]-{Phi} relations show the least intrinsic scatter as well as the least residual trend with galaxy size. In this work we study the ages and metallicities measured from full spectral fitting of 2085 star-forming galaxies (SFGs) from the SDSS Legacy Survey, selected so all galaxies in the sample are probed to one effective radius. As with the trends found in ETGs, we find that in SFGs age correlates best with stellar surface mass density, and [Z/H] correlates best with gravitational potential. We discuss multiple mechanisms that could lead to these scaling relations. For the [Z/H]-{Phi} relation we conclude that gravitational potential is the primary regulator of metallicity, via its relation to the gas escape velocity. The age-{Sigma} relation is consistent with compact galaxies forming earlier, as higher gas fractions in the early universe cause old galaxies to form more compactly during their in situ formation phase, and may be reinforced by compactness-related quenching mechanisms.
639. Agglomerate of early-type Hipparcos stars
ID:
ivo://CDS.VizieR/J/AN/329/801
Title:
Agglomerate of early-type Hipparcos stars
Short Name:
J/AN/329/801
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the spatial structure and sub-structure of regions rich in Hipparcos stars with blue BT-VT colours. These regions, which comprise large stellar complexes, OB associations, and young open clusters, are tracers of on-going star formation in the Galaxy. The DBSCAN (Density-Based Spatial Clustering of Applications with Noise) data clustering algorithm is used to look for spatial overdensities of early-type stars. Once an overdensity, "agglomerate", is identified, we carry out a data and bibliographic compilation of their star member candidates. The actual membership in agglomerate of each early-type star is studied based on its heliocentric distance, proper motion, and previous spectro-photometric information. We identify 35 agglomerates of early-type Hipparcos stars. Most of them are associated to previously known clusters and OB associations. The previously unknown P Puppis agglomerate is subject of a dedicated study with Virtual Observatory tools.
640. A 6.7GHz methanol maser survey. II. |b|<2{deg}
ID:
ivo://CDS.VizieR/J/ApJS/241/18
Title:
A 6.7GHz methanol maser survey. II. |b|<2{deg}
Short Name:
J/ApJS/241/18
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results of our systematic survey for Galactic 6.7GHz Class II CH_3_OH maser emission toward a sample of young stellar objects. The survey was conducted with the Shanghai Tianma Radio Telescope (TMRT). The sample consists of 3348 sources selected from the all-sky Wide-field Infrared Survey Explorer (WISE) point-source catalog. We discussed the selection criteria in detail and the detection results of those at high Galactic latitudes (i.e., |b|>2{deg}) in a previous paper (Paper I; Yang+ 2017, J/ApJ/846/160). Here, we present the results from the survey of those at low Galactic latitudes, i.e., |b|<2{deg}. Of 1875 selected WISE point sources, 291 positions that were actually associated with 224 sources that were detected with CH_3_OH maser emission. Among them, 32 are newly detected. A majority of the newly detected sources are associated with bright WISE sources. The majority of the detected sources (209/224=93.3%) are quite close to the Galactic Plane (|b|<1{deg}) and lie on the inner spiral arms with positive local standard of rest velocities. The detection rate and the color-color distribution of our detection are all matched with our anticipation. Combining with detections from previous surveys, we compile a catalog of 1085 sources with 6.7GHz CH_3_OH maser emission in our Galaxy.

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