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Brightest Cluster Galaxies (brightest + cluster_galaxy)
Selected AbstractsPhotometric properties and scaling relations of early-type Brightest Cluster GalaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008F. S. Liu ABSTRACT We investigate the photometric properties of the early-type Brightest Cluster Galaxies (BCGs) using a carefully selected sample of 85 BCGs from the C4 cluster catalogue with a redshift of less than 0.1. We perform accurate background subtractions and surface photometry for these BCGs to 25 mag arcsec,2 in the Sloan r band. By quantitatively analysing the gradient of the Petrosian profiles of BCGs, we find that a large fraction of BCGs have extended stellar envelopes in their outskirts; more luminous BCGs tend to have more extended stellar haloes that are likely to be connected with mergers. A comparison sample of elliptical galaxies was chosen with similar apparent magnitude and redshift ranges, for which the same photometric analysis procedure is applied. We find that BCGs have steeper size,luminosity (R,L,) and Faber,Jackson (L,,,) relations than the bulk of early-type galaxies. Furthermore, the power-law indices (, and ,) in these relations increase as the isophotal limits become deeper. For isophotal limits from 22 to 25 mag arcsec,2, BCGs are usually larger than the bulk of early-type galaxies, and a large fraction (,49 per cent) of BCGs have discy isophotal shapes. The differences in the scaling relations are consistent with a scenario where the dynamical structure and formation route of BCGs may be different from the bulk of early-type galaxies; in particular dry (dissipationless) mergers may play a more important role in their formation. We highlight several possible dry merger candidates in our sample. [source] Major dry mergers in early-type brightest cluster galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2009F. S. Liu ABSTRACT We search for ongoing major dry mergers in a well-selected sample of local brightest cluster galaxies (BCGs) from the C4 cluster catalogue. 18 out of 515 early-type BCGs with redshift between 0.03 and 0.12 are found to be in major dry mergers, which are selected as pairs (or triples) with r -band magnitude difference ,mr < 1.5 and projected separation rp < 30 kpc, and showing signatures of interaction in the form of significant asymmetry in residual images. We find that the fraction of BCGs in major dry mergers increases with the richness of the clusters, consistent with the fact that richer clusters usually have more massive (or luminous) BCGs. We estimate that present-day early-type BCGs may have experienced on average ,0.6 (tmerge/0.3 Gyr),1 major dry mergers and through this process increases their luminosity (mass) by 15 per cent (tmerge/0.3 Gyr),1 (fmass/0.5) on average since z= 0.7, where tmerge is the merging time-scale and fmass is the mean mass fraction of companion galaxies added to the central ones. We also find that major dry mergers do not seem to elevate radio activities in BCGs. Our study shows that major dry mergers involving BCGs in clusters of galaxies are not rare in the local Universe, and they are an important channel for the formation and evolution of BCGs. [source] The evolution of the galaxy red sequence in simulated clusters and groupsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008A. D. Romeo ABSTRACT N -body/hydrodynamical simulations of the formation and evolution of galaxy groups and clusters in a , cold dark matter (,CDM) cosmology are used in order to follow the building-up of the colour,magnitude relation in two clusters and in 12 groups. We have found that galaxies, starting from the more massive, move to the red sequence (RS) as they get aged over times and eventually set upon a ,dead sequence' (DS) once they have stopped their bulk star formation activity. Fainter galaxies keep having significant star formation out to very recent epochs and lie broader around the RS. Environment plays a role as galaxies in groups and cluster outskirts hold star formation activity longer than the central cluster regions. However, galaxies experiencing infall from the outskirts to the central parts keep star formation on until they settle on to the DS of the core galaxies. Merging contributes to mass assembly until z, 1, after which major events only involve the brightest cluster galaxies. The emerging scenario is that the evolution of the colour,magnitude properties of galaxies within the hierarchical framework is mainly driven by star formation activity during dark matter haloes assembly. Galaxies progressively quenching their star formation settle to a very sharp ,red and dead' sequence, which turns out to be universal, its slope and scatter being almost independent of the redshift (since at least z, 1.5) and environment. Differently from the DS, the operatively defined RS evolves more evidently with z, the epoch when it changes its slope being closely corresponding to that at which the passive galaxies population takes over the star-forming one: this goes from z, 1 in clusters down to 0.4 in normal groups. [source] The properties of fossil groups of galaxiesASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009P. Eigenthaler Abstract Numerical simulations as well as optical and X-ray observations over the last few years have shown that poor groups of galaxies can evolve to what is called a fossil group. Dynamical friction as the driving process leads to the coalescence of individual galaxies in ordinary poor groups leaving behind nothing more than a central, massive elliptical galaxy supposed to contain the merger history of the whole group. Due to merging timescales for less-massive galaxies and gas cooling timescales of the X-ray intragroup medium exceeding a Hubble time, a surrounding faint-galaxy population having survived this galactic cannibalism as well as an extended X-ray halo similar to that found in ordinary groups, is expected. Recent studies suggest that fossil groups are very abundant and could be the progenitors of brightest cluster galaxies (BCGs) in the centers of rich galaxy clusters. However, only a few objects are known to the literature. This article aims to summarize the results of observational fossil group research over the last few years and presents ongoing work by the authors. Complementary to previous research, the SDSS and RASS surveys have been cross-correlated to identify new fossil structures yielding 34 newly detected fossil group candidates. Observations with ISIS at the 4.2 m William Herschel Telescope on La Palma have been carried out to study the stellar populations of the central ellipticals of 6 fossil groups. In addition multi-object spectroscopy with VLTs VIMOS has been performed to study the shape of the OLF of one fossil system (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||