- ID:
- ivo://CDS.VizieR/J/ApJ/700/103
- Title:
- Ages of star clusters in M33
- Short Name:
- J/ApJ/700/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a result of age estimation for star clusters in M33. We obtain color-magnitude diagrams (CMDs) of resolved stars in 242 star clusters from the Hubble Space Telescope/Wide Field Planetary Camera 2 images. We estimate ages of 100 star clusters among these, by fitting the Padova theoretical isochrones to the observational CMDs. Age distribution of the star clusters shows a dominant peak at log(t)~7.8. Majority of star clusters are younger than log(t)=9.0, while 10 star clusters are older than log(t)~9.0. There is only one cluster younger than log(t)=7 in this study, which is in contrast with the results based on the integrated photometry of star clusters in the previous studies. Radial distribution of the cluster ages shows that young- to intermediate-age clusters are found from the center to the outer region, while old clusters are distributed farther from the M33 center. We briefly discuss the implication of the results with regard to the formation of the M33 cluster system.
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- 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.
- 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.
- 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).
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/MNRAS/407/2399
- Title:
- AGN activity and black hole mass
- Short Name:
- J/MNRAS/407/2399
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the role of host galaxy classification and black hole mass (MBH) in a heterogeneous sample of 276 mostly nearby (z<0.1) X-ray and IR-selected active galactic nuclei (AGN).
- ID:
- ivo://CDS.VizieR/J/other/RMxAA/47.361
- Title:
- AGN activity in isolated SDSS galaxies
- Short Name:
- J/other/RMxAA/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss the nature and origin of the nuclear activity observed in a sample of 292 SDSS narrow-emission-line galaxies, considered to have formed and evolved in isolation. All these galaxies are spiral like and show some kind of nuclear activity. The fraction of Narrow Line AGNs (NLAGNs) and Transition type Objects (TOs; a NLAGN with circumnuclear star formation) is relatively high, amounting to 64% of the galaxies. There is a definite trend for the NLAGNs to appear in early-type spirals, while the star forming galaxies and TOs are found in later-type spirals. We verify that the probability for a galaxy to show an AGN characteristic increases with the bulge mass of the galaxy (Torres-Papaqui et al. 2011), and find evidence that this trend is really a by-product of the morphology, suggesting that the AGN phenomenon is intimately connected with the formation process of the galaxies. Consistent with this interpretation, we establish a strong connection between the astration rate -- the efficiency with which the gas is transformed into stars - the AGN phenomenon, and the gravitational binding energy of the galaxies: the higher the binding energy, the higher the astration rate and the higher the probability to find an AGN. The NLAGNs in our sample are consistent with scaled-down or powered-down versions of quasars and Broad Line AGNs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/968
- Title:
- AGN automatic photometric classification
- Short Name:
- J/MNRAS/437/968
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we discuss an application of machine-learning-based methods to the identification of candidate active galactic nucleus (AGN) from optical survey data and to the automatic classification ofAGNs in broad classes. We applied four different machine-learning algorithms, namely the Multi Layer Perceptron, trained, respectively, with the Conjugate Gradient, the Scaled Conjugate Gradient, the Quasi Newton learning rules and the Support Vector Machines, Q4 to tackle the problem of the classification of emission line galaxies in different classes, mainly AGNs versus non-AGNs, obtained using optical photometry in place of the diagnostics based on line intensity ratios which are classically used in the literature. Using the same photometric features, we discuss also the behaviour of the classifiers on finer AGN classification tasks, namely Seyfert I versus Seyfert II, and Seyfert versus LINER. Furthermore, we describe the algorithms employed, the samples of spectroscopically classified galaxies used to train the algorithms, the procedure followed to select the photometric parameters and the performances of our methods in terms of multiple statistical indicators. The results of the experiments show that the application of self-adaptive data mining algorithms trained on spectroscopic data sets and applied to carefully chosen photometric parameters represents a viable alternative to the classical methods that employ time-consuming spectroscopic observations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/499/4325
- Title:
- AGN contrib. of interac. galaxies
- Short Name:
- J/MNRAS/499/4325
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Emission from active galactic nuclei (AGNs) is known to play an important role in the evolution of many galaxies including luminous and ultraluminous systems (U/LIRGs), as well as merging systems. However, the extent, duration, and exact effects of its influence are still imperfectly understood, as are the conditions that lead to it dominating the IR emission, and then fading again after coalescence. To assess the impact of AGNs on interacting systems, we present a Spectral Energy Distribution (SED) analysis of a sample of 188 nearby galaxies We gather and systematically re-reduce archival broad-band imaging mosaics from the ultraviolet to the far-infrared using data from GALEX, SDSS, 2MASS, IRAS, WISE, Spitzer, and Herschel. We use spectroscopy from Spitzer/IRS to obtain fluxes from fine-structure lines that trace star formation and AGN activity. Utilizing the SED modelling and fitting tool CIGALE, we derive the physical conditions of the interstellar medium, both in star-forming regions and in nuclear regions dominated by the AGN in these galaxies. We investigate how the star formation rates (SFRs) and the fractional AGN contributions (fAGN) depend on stellar mass, galaxy type, and merger stage. We find that luminous galaxies more massive than about 10^10M* are likely to deviate significantly from the conventional galaxy main-sequence relation. Interestingly, infrared AGN luminosity and stellar mass in this set of objects are much tighter than SFR and stellar mass. We find that buried AGNs may occupy a locus between bright starbursts and pure AGNs in the fAGN-[NeV]/[NeII] plane. We identify a modest correlation between fAGN and mergers in their later stages.
