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Register a new userGalaxy Clusters in the Line of Sight to Background Quasars: II. Environmental effects on the sizes of baryonic halo sizes
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Nelson David Padilla
Publication date
2009
fields
Physics
and research's language is
English
Authors
N. Padilla
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Based on recent results on the frequency of MgII absorption line systems in the QSO behind RCS clusters survey (QbC), we analyse the effects of the cluster environment on the sizes of baryonic haloes around galaxies. We use two independent models, i) an empirical halo occupation model which fits current measurements of the clustering and luminosity function of galaxies at low and high redshifts, and ii) the GALFORM semi-analytic model of galaxy formation, which follows the evolution of the galaxy population from first principles, adjusted to match the statistics of low and high redshift galaxies. In both models we constrain the MgII halo sizes of field and cluster galaxies using observational results on the observed MgII statistics. Our results for the field are in good agreement with previous works, indicating a typical mgii halo size of $r_MgII ~ 50h_71^-1kpc in the semi-analytic model, and slightly lower in the halo occupation number approach. For the cluster environment, we find that both models require a median MgII halo size of r_MgII< 10h_71^-1kpc in order to reproduce the observed statistics on absorption line systems in clusters of galaxies. Based on the Chen & Tinker (2008) result that stronger systems occur closer to the MgII halo centre, we find that strong absorption systems in clusters of galaxies occur at roughly a fixed fraction of the cold-warm halo size out to 1h_71^-1Mpc from the cluster centres. In contrast, weaker absorption systems appear to occur at progressively shorter relative fractions of this halo as the distance to the cluster centre decreases.
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We present a study of galaxy sizes in the local Universe as a function of galaxy environment, comparing clusters and the general field. Galaxies with radii and masses comparable to high-z massive and compact galaxies represent 4.4% of all galaxies more massive than 3 X 10^{10} M_sun in the field. Such galaxies are 3 times more frequent in clusters than in the field. Most of them are early-type galaxies with intermediate to old stellar populations. There is a trend of smaller radii for older luminosity-weighted ages at fixed galaxy mass. We show the relation between size and luminosity-weighted age for galaxies of different stellar masses and in different environments. We compare with high-z data to quantify the evolution of galaxy sizes. We find that, once the progenitor bias due to the relation between galaxy size and stellar age is removed, the average amount of size evolution of individual galaxies between high- and low-z is mild, of the order of a factor 1.6.
The dependence of the luminosity function of cluster galaxies on the evolutionary state of the parent cluster is still an open issue, in particular as concern the formation/evolution of the brightest cluster galaxies. We plan to study the bright part of the LFs of a sample of very unrelaxed clusters (DARC clusters showing evidence of major, recent mergers) and compare them to a reference sample of relaxed clusters spanning a comparable mass and redshift range. Our analysis is based on the SDSS DR7 photometric data of ten, massive, and X-ray luminous clusters (0.2<z<0.3), always considering physical radii (R_200 or its fractions). We consider r band LFs and use the color-magnitude diagrams (r-i,r) to clean our samples as well to consider separately red and blue galaxies. We find that DARC and relaxed clusters give similar LF parameters and blue fractions. The two samples differ for their content of bright galaxies BGs, M_r<-22.5, since relaxed clusters have fewer BGs, in particular when considering the outer cluster region 0.5R_200<R<R_200 (by a factor two). However, the cumulative light in BGs is similar for relaxed and DARC samples. We conclude that BGs grow in luminosity and decrease in number as the parent clusters grow hierarchically in agreement with the BG formation by merging with other luminous galaxies.
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