- ID:
- ivo://CDS.VizieR/J/AJ/125/2393
- Title:
- A2256 galaxies redshifts and 1.4GHz fluxes
- Short Name:
- J/AJ/125/2393
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Abell 2256 is a nearby (z~0.06), rich cluster of galaxies with fascinating observed properties across a range of wavelengths. Long believed to represent a cluster merger, recent X-ray and optical results have suggested that in addition to the primary cluster and subcluster there is evidence for a third, poorer system. We present wide-field high-sensitivity 1.4GHz VLA radio observations of Abell 2256 in conjunction with optical imaging and additional spectroscopy. Over 40 cluster radio galaxies are identified, with optical spectroscopy indicating the emission source (star formation or active galactic nucleus) for most of them. While the overall fraction of galaxies exhibiting radio emission is consistent with a large sample of other nearby clusters, we find an increase in the activity level of galaxies belonging to the third system (hereafter "the Group"). Specifically, the Group has relatively more star formation than both the primary cluster and main subcluster. The position of the Group is also coincident with the observed cluster radio relic. We suggest that the Group recently (0.3Gyr) merged with the primary cluster and that this merger, not the ongoing merger of the primary and the main subcluster, might be responsible for many of the unusual radio properties of Abell 2256. Furthermore, the greater star formation activity of the Group suggests that the infall of groups is an important driver of galaxy evolution in clusters.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/495/15
- Title:
- A959 galaxies r' magnitude and radial velocities
- Short Name:
- J/A+A/495/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The connection of cluster mergers with the presence of extended, diffuse radio sources in galaxy clusters is still being debated. We aim to obtain new insights into the internal dynamics of Abell 959, showing evidence of a diffuse radio source, analyzing velocities and positions of member galaxies. Our analysis is based on redshift data for 107 galaxies in the cluster field acquired at the Telescopio Nazionale Galileo. We also use photometric data from the Sloan Digital Sky Survey (Data Release 6). We combine galaxy velocities and positions to select 81 galaxies recognized as cluster members and determine global dynamical properties. We analyze the cluster searching for substructures by using the weighted gap analysis, the KMM method and the Dressler-Shectman statistics. We also study the 2D galaxy distribution in the field of the cluster. We compare our results with those from X-ray and gravitational lensing analyses.
- ID:
- ivo://CDS.VizieR/J/ApJS/192/6
- Title:
- A GALEX UV imaging survey of nearby galaxies
- Short Name:
- J/ApJS/192/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a GALEX ultraviolet (UV) survey of a complete sample of 390 galaxies within ~11Mpc of the Milky Way. The UV data are a key component of the composite Local Volume Legacy, an ultraviolet-to-infrared imaging program designed to provide an inventory of dust and star formation in nearby spiral and irregular galaxies. The ensemble data set is an especially valuable resource for studying star formation in dwarf galaxies, which comprise over 80% of the sample. We describe the GALEX survey programs that obtained the data and provide a catalog of far-UV (~1500{AA}) and near-UV (~2200{AA}) integrated photometry. General UV properties of the sample are briefly discussed. We compute two measures of the global star formation efficiency, the star formation rate (SFR) per unit HI gas mass, and the SFR per unit stellar mass, to illustrate the significant differences that can arise in our understanding of dwarf galaxies when the FUV is used to measure the SFR instead of H{alpha}.
- ID:
- ivo://CDS.VizieR/J/A+A/421/509
- Title:
- AGAPE catalogue of M31 variables
- Short Name:
- J/A+A/421/509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the AGAPE astrometric and photometric catalogue of 1579 variable stars in a 14' x 10' field centred on M31. Each variable star in the catalogue is identified as AGPVm, m running from 1 to 1579. Then are given: Fn(x,y) (F being the letter of identification of AGAPE field and n the variable star number in this field; x and y being the pixel coordinates in the reference frame), right ascension and declination for 2000.0, R_max_ magnitude at observed maximum, and L the likelihood function. When the variable star is a nova discovered by eye, no L value is given.
- ID:
- ivo://CDS.VizieR/J/A+A/574/A102
- Title:
- AGB candidates in NGC 6822
- Short Name:
- J/A+A/574/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ratio of C- and M-type asymptotic giant branch (AGB) stars is commonly used to estimate the metallicity of extragalactic populations. Sources in the AGB population must therefore be accurately classified as either C- or M-type. Spectroscopic data are presented for candidate C- and M-type AGB stars, previously classified using JHK photometry, in the Local Group dwarf galaxy NGC 6822. This paper aims to evaluate the success of the JHK classification criteria used in order to determine the level of error associated with this method, and to refine the criteria for future studies. The success rate of a second independent method of source classification, the CN-TiO method, is also examined. We also review the validity of the 4kpc radial limit imposed in our previous work. Spectra of 323 sources, distributed across an area of 2deg^2^, were taken using the AAOmega multi-fibre spectrograph on the Anglo-Australian Telescope and have been classified using an automated classification system and spectral standards from the literature. Nearly half (135) of these sources were selected in common with a photometric catalogue that relied on the CN-TiO method. Within this sample we were able to classify 158 sources, including 82 C-type giants and one anomalous M-type giant, all members of NGC 6822, and 75 foreground K- and M-type dwarf sources. All but three of the giant sources are located within 3 kpc of the galactic centre. Using this spectroscopic sample, new JHK photometric criteria for the isolation and classification of C- and M-type AGB stars have been derived. The error rate in the CN-TiO method, arising from stars incorrectly classified as C-type, has been estimated to be ~7%. Based on the new JHK classification criteria, revised estimates of the global C/M ratio, 0.95+/-0.04, and iron abundance, -1.38+/-0.06dex, are presented for NGC 6822.
- ID:
- ivo://CDS.VizieR/J/A+A/540/A135
- Title:
- AGB population of NGC 6822
- Short Name:
- J/A+A/540/A135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6822 is an irregular dwarf galaxy and part of the Local Group. Its close proximity and apparent isolation provide a unique opportunity to study galactic evolution without any obvious strong external influences. This paper aims to study the spatial distribution of the asymptotic giant branch (AGB) population and metallicity in NGC 6822. Using deep, high quality JHK photometry, taken with WFCAM on UKIRT, carbon- and oxygen-rich AGB stars have been isolated. The ratio between their number, the C/M ratio, has then been used to derive the [Fe/H] abundance across the galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/530/A58
- Title:
- AGB stars in Cen A dwarf galaxies
- Short Name:
- J/A+A/530/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the resolved stellar content of early-type dwarf galaxies in the Centaurus A group, to estimate their intermediate-age population fractions. We use near-infrared photometric data taken with the VLT/ISAAC instrument, together with previously analyzed archival HST/ACS data. The combination of the optical and infrared wavelength range permits us to firmly identify luminous asymptotic giant branch stars, which are indicative of an intermediate-age population in these galaxies. We consider one dwarf spheroidal (CenA-dE1) and two dwarf elliptical (SGC1319.1-4216 and ESO269-066) galaxies that are dominated by an old population. The most recent periods of star formation are estimated to have taken place between 2 and 5Gyr ago for SGC1319.1-4216 and ESO269-066, and approximately 9Gyr ago for CenA-dE1. For ESO269-066, we find that the intermediate-age populations are significantly more centrally concentrated than the predominantly old underlying stars. The intermediate-age population fraction is found to be small in the target galaxies, consistent with fractions of up to 15% of the total population. These values might be larger by a factor of two or three, if we considered the observational limitations and the recent discussion about the uncertainties in theoretical models. We suggest that there is a correlation between intermediate-age population fraction and proximity to the dominant group galaxy, with closer dwarfs having slightly smaller fractions, although our sample is too small to draw firm conclusions. Even when considering our results as lower limits, the intermediate-age population fractions for the studied dwarfs are clearly much smaller than those found in similar dwarfs around the Milky Way, but comparable to what is seen for the low-mass M31 companions. Our results confirm our previous work about early-type dwarfs in the Centaurus A group.
- ID:
- ivo://CDS.VizieR/J/MNRAS/394/795
- Title:
- AGB stars in Fornax dwarf spheroidal galaxy
- Short Name:
- J/MNRAS/394/795
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a multi-epoch study of the Fornax dwarf spheroidal galaxy, made with the Infrared Survey Facility, over an area of about 42x42arcmin^2^. The colour-magnitude diagram shows a broad well-populated giant branch with a tip that slopes downwards from red to blue, as might be expected given Fornax's known range of age and metallicity. The extensive asymptotic giant branch (AGB) includes seven Mira variables and 10 periodic semiregular variables. Five of the seven Miras are known to be carbon rich. Their pulsation periods range from 215 to 470d, indicating a range of initial masses. Three of the Fornax Miras are redder than typical Large Magellanic Cloud (LMC) Miras of similar period, probably indicating particularly heavy mass-loss rates. Many, but not all, of the characteristics of the AGB are reproduced by isochrones from Marigo et al. (2008A&A...482..883M) for a 2Gyr population with a metallicity of Z=0.0025.
- ID:
- ivo://CDS.VizieR/J/MNRAS/385/1270
- Title:
- Age-metallicity relation via photometry
- Short Name:
- J/MNRAS/385/1270
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a widely used stellar-population synthesis model, we study the possibility of using pairs of AB system colours to break the well-known stellar age-metallicity degeneracy and to give constraints on two luminosity-weighted stellar-population parameters (age and metallicity). We present the relative age and metallicity sensitivities of the AB system colours that relate to the u, B, g, V, r, R, i, I, z, J,H and K bands, and we quantify the ability of various colour pairs to break the age-metallicity degeneracy. The results also show that the stellar ages and metallicities of galaxies observed by the Sloan Digital Sky Survey and the Two-Micron All-Sky Survey can be estimated via photometry data.
- ID:
- ivo://CDS.VizieR/J/A+A/549/A60
- Title:
- Ages and [Fe/H] of M31 globular clusters
- Short Name:
- J/A+A/549/A60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation and evolution of disk galaxies are long standing questions in Astronomy. Understanding the properties of globular cluster systems can lead to important insights on the evolution of its host galaxy. We aim to obtain the stellar population parameters - age and metallicity - of a sample of M31 and Galactic globular clusters. Studying their globular cluster systems is an important step towards understanding their formation and evolution in a complete way.
