Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
The early-type dwarf galaxy population of the Hydra I cluster
Aims: We analyse the properties of the early-type dwarf galaxypopulation (MV > -17 mag) in the Hydra I cluster. Weinvestigate the galaxy luminosity function (LF), the colour-magnituderelation (CMR), and the magnitude-surface brightness relation down toMV ~ -10 mag. Another goal of this study is to findcandidates for ultra-compact dwarf galaxies (UCDs) in Hydra I. Methods: Two spectroscopic surveys performed with Magellan I/LDSS2 atLas Campanas Observatory and VLT/VIMOS, as well as deep VLT/FORS1 imagesin V and I bands, covering the central parts of the cluster, wereexamined. We identify cluster members by radial velocity measurementsand select other cluster galaxy candidates by their morphology and lowsurface brightness. The candidates' total magnitudes and central surfacebrightnesses were derived from the analysis of their surface brightnessprofiles. To determine the faint-end slope of the LF, the galaxy numbercounts are completeness corrected. Results: We obtain radialvelocities for 126 objects and identify 32 cluster members, of which 5are previously uncatalogued dwarf galaxies. One possible UCD candidatewith MV = -13.26 mag is found. Our sample of ?100morphologically selected dwarf galaxies with M_V>-17 mag defines aCMR that extends the CMR of the giant cluster galaxies to the magnitudelimit of our survey (MV ~ -10 mag). It matches the relationsfound for the Local Group (LG) and the Fornax cluster dwarf galaxiesalmost perfectly. The Hydra I dwarf galaxies also follow amagnitude-surface brightness relation that is very similar to that ofthe LG dwarf galaxies. Moreover, we observe a continuous relation fordwarf galaxies and giant early-type galaxies when plotting the centralsurface brightness ?0 of a Sérsic model vs. thegalaxy magnitude. The effective radius is found to be largelyindependent of the luminosity for MV > -18 mag. It isconsistent with a constant value of Re ~ 0.8 kpc. We presentthe photometric parameters of the galaxies as the Hydra I ClusterCatalogue (HCC). By fitting a Schechter function to the luminositydistribution, we derive a very flat faint-end slope of the LF (? =-1.13 ± 0.04), whereas fitting a power law for MV >-14 mag gives ? = -1.40 ± 0.18. Conclusions: Ourfindings of a continuous CMR and ?0 - MVrelation for dwarf and giant early-type galaxies suggests that they arethe same class of objects. The similarity of those relations to otherenvironments like the LG implies that internal processes could be moreimportant for their global photometric properties than externalinfluences.Based on observations obtained at the European Southern Observatory,Chile (Observing Programmes 065.N-0459(A) and 076.B-0293).Appendix A is only available in electronic form at http://www.aanda.org
| Galaxy Luminosity Functions from Deep Spectroscopic Samples of Rich Clusters
Using a new spectroscopic sample and methods accounting forspectroscopic sampling fractions that vary in magnitude and surfacebrightness, we present R-band galaxy luminosity functions (GLFs) for sixnearby galaxy clusters with redshifts of 4000 kms-1
| FLASH redshift survey - I. Observations and catalogue
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of4613 galaxies brighter than bJ= 16.7 (corrected for Galacticextinction) over a 700-deg2 region of sky in the generaldirection of the Local Group motion. The survey region is a70°× 10° strip spanning the sky from the ShapleySupercluster to the Hydra cluster, and contains 3141 galaxies withmeasured redshifts. Designed to explore the effect of the galaxyconcentrations in this direction (in particular the Supergalactic planeand the Shapley Supercluster) upon the Local Group motion, the 68 percent completeness allows us to sample the large-scale structure betterthan similar sparsely-sampled surveys. The survey region does notoverlap with the areas covered by ongoing wide-angle (Sloan or 2dF)complete redshift surveys. In this paper, the first in a series, wedescribe the observation and data reduction procedures, the analysis forthe redshift errors and survey completeness, and present the surveydata.
| Streaming motions of galaxy clusters within 12 000 km s-1 - II. New photometric data for the Fundamental Plane
We present new R-band photometric data for 447 galaxies, gathered forthe `Streaming Motions of Abell Clusters' (SMAC) project. The datacomprise 629 individual measurements of the Fundamental Plane (FP)parameters effective radius (Re) and surface brightness(<μ>e), derived from r1/4-law profilefitting. More than a third of the galaxies were observed more than once.The photometric precision is ~0.02mag as judged from comparisons ofaperture photometry between repeat observations of galaxies. ThecombinationXfp=logRe-0.33<μ>e, whichenters into the Fundamental Plane relation, has internal uncertaintiesof ~0.008, corresponding to <2 per cent in estimated distance. Takenindividually, the (correlated) internal errors in Re and<μ>e are ~8 per cent and ~0.12mag respectively.Comparisons with literature data constrain the external random errors to<~5 per cent in distance (per observation), which is small incomparison to the ~20 per cent scatter in the FP. The data will formpart of a merged catalogue of FP parameters, presented in a companionpaper.
| A catalogue of Mg_2 indices of galaxies and globular clusters
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 130.79.128.5. Table 2 is available both in text and electronic form.
| Hα objective prism survey of Abell 1060
As part of a continuing study of the effect of cluster environment onthe star formation properties of galaxies, we have undertaken anHα objective prism survey of the nearby cluster, Abell 1060. Wedetect 33 galaxies in emission, 24 of which are cluster members. Wepresent new radial velocity measurements and Hα + [N Ii]equivalent widths and fluxes for a number of these galaxies. Wedistinguish between galaxies with diffuse and compact emission, thelatter having been associated in previous work with a disturbedmorphology of the galaxy and most likely resulting from tidally-inducedstar formation from galaxy-galaxy or cluster-galaxy interactions. Thefraction of cluster spirals in Abell 1060 detected with compact emissionagrees with the expected fraction for a cluster of its richness, asderived from results of a previous survey of 8 clusters. Some of thedetected cluster early-type spirals exhibit anomalously high globalHα equivalent widths, as compared to galaxies of similar type inthe field.
| Stellar populations of cluster E and S0 galaxies
Spectral line index data for a sample of 290 E and S0 galaxies are usedto investigate the stellar populations of these galaxies. 250 of thegalaxies are members of 11 nearby clusters (cz_CMB<11500 km s^-1). Westudy how the stellar populations of the galaxies are related to thevelocity dispersions, the masses of the galaxies, and the clusterenvironment. This is done by establishing relations between theseparameters and the line indices Mg_2, and Hβ_G. Thedifference between the slope of the Mg_2-sigma relation and the slope ofthe -sigma relation indicates that the abundance ratio [Mg/Fe]is 0.3-0.4 dex higher for galaxies with velocity dispersions of 250 kms^-1 compared to galaxies with velocity dispersions of 100 km s^-1. Thisis in agreement with previous estimates by Worthey et al. The index is more strongly correlated with the projected cluster surfacedensity, rho_cluster, than with the galactic mass or the velocitydispersion. Earlier we found that the residuals for the Mg_2-sigmarelation depend on the cluster environment. Here we determine how boththe Mg_2 index and the index depend on the velocitydispersion and rho_cluster. Alternative explanations that could create aspurious environment dependence are discussed. No obvious alternativesare found. The environment dependence of the Mg_2-sigma relation issupported by data from Faber et al. The dependence on the environmentimplies that [Mg/Fe] decreases with increasing density, rho_cluster. Thedecrease in [Mg/Fe] is 0.1 dex over 2.5 dex in rho_cluster. We have alsostudied the extent to which the mass-to-light (M/L) ratios of thegalaxies are determined by the stellar populations. The M/L ratios arestrongly correlated with the indices Mg_2 and Hβ_G, while the index is only weakly correlated with the M/L ratio. Based oncurrent stellar population models, we find that it is not yet possibleto derive unique physical parameters (mean age, mean abundances, meanIMF, and fraction of dark matter) from the observables (line indices,velocity dispersion, mass, M/L ratio).
| Structure and kinematics of galaxy clusters. I. The redshift catalogue.
An extensive redshift survey has been conducted on a sample of 15 nearby(0.01<~z<~0.05) clusters of galaxies. A total number of 860redshifts were determined by fitting of emission-lines and/orcross-correlation techniques. Of this sample, 735 galaxies are within0.2-0.8Mpc (H_0_=50km/s/Mpc) of the center of clusters. Approximatemorphological types are available for most of the galaxies. A comparisonof the present redshifts with published data allows an extensive erroranalysis. The agreement is excellent with the most modern data, showinga zero point error of 5km/s and an overall consistency of themeasurements and their uncertainties. We estimate our redshifts to havemean random errors around 30km/s. A population analysis of the clusterswill be given in a forthcoming paper.
| Spectroscopy for E and S0 galaxies in nine clusters
Central velocity dispersions, Mg_2 line indices and radial velocitiesfor 220 E and S0 galaxies are derived on the basis of intermediateresolution spectroscopy. Galaxies in the following clusters have beenobserved: Abell 194, Abell 539, Abell 3381, Abell 3574, S639, S753,Doradus, HydraI (Abell 1060) and Grm 15. For 151 of the galaxies, thevelocity dispersion has not previously been measured. 134 of the Mg_2determinations are for galaxies with no previous measurement. Thespectra cover either 500 or 1000A, centred on the magnesium triplet at5177A. The observations were obtained with the Boller & Chivensspectrograph at the ESO 1.5-m telescope and with the OPTOPUS, amulti-object fibre-fed B&C spectrograph, at the ESO 3.6-m telescope.The data are part of our ongoing study of the large-scale motions in theUniverse and the physical background for the Fundamental Plane. TheFourier fitting method was used to derive the velocity dispersions andradial velocities. The velocity dispersions have been corrected for theeffect of the size of the aperture. The correction was established onthe basis of velocity dispersion profiles available in the literature. Acomparison with results from Davies et al. shows that the derivedcentral velocity dispersions have an rms error of 0.036 in logsigma.There is no offset relative to the velocity dispersions from Davies etal. The offset relative to data from Lucey & Carter is-0.017+/-0.011 in logsigma, with our velocity dispersions being thesmallest. The velocity dispersions derived from the B&C and theOPTOPUS observations, as well as the velocity dispersions published byDavies et al., Dressler, Lucey & Carter and Lucey et al., can bebrought on a system consistent within 3 per cent. The Mg_2 line indiceshave been corrected for the size of the apertures, transformed to theLick system, and corrected for the effect of the velocity dispersion.From comparison with data from Davies et al. and from Faber, we findthat the rms error of Mg_2 is 0.013. Comparisons of the radialvelocities with data from the literature show that our determinationsare accurate to within ~=35 km s^-1. The accuracies reached for theseobservations are adequate for the study of the large-scale motions inthe Universe and for investigations of the Fundamental Plane.
| The Hydra I cluster of galaxies. V - A catalogue of galaxies in the cluster area
The available information for 581 galaxies in the area of the Hydra I (= Abell 1060) cluster is compiled into a catalog. Positions, magnitudes,diameters, position angles, radial velocities, and morphological typesare given. A first determination of the luminosity function of Hydra Iis attempted. An assessment of the photometric errors in the isophotalmagnitudes is included.
| The Hydra I cluster of galaxies - A unique case of membership definition
New optical radial velocities for 71 galaxies in the Hydra I cluster arepresented. The recession velocity of the cluster is determined to 3425km/sec, yielding a distance of about 45.7 Mpc. The overall velocitydispersion is 676 km/sec. Results of galaxy counts could be fitted by atwo-component model. Many of the global cluster properties of Hydra Ilike, e.g., total galaxy content, velocity dispersion, X-ray flux, etc.,suggest a remarkable similarity with the Virgo cluster. No foregroundgalaxies and no background galaxies were noted in the observed area upto about 8000 km/sec, suggesting regions of empty space of the order of40-50 Mpc extent along the line of sight.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
Cataloghi e designazioni:
|
