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Galaxy Evolution Galaxy evoluon: Transformaon in the suburbs of clusters Smri% Mahajan University of Queensland, Brisbane Star formation-densityMorphology-Density Relaon relation Outskirts of clusters E S0 Clusters Spirals Balogh et al. 2003 Environment => local Field projected galaxy density Dressler 1980 12th December 2012 [email protected] Why I want to study environment? • How do the galaxies in high density regions become passive? • What is the impact, if any, of the large-scale (≥10 Mpc) structure on galaxy observables? • Which environmental mechanisms are important? Do they have the same impact on all types of galaxies? SFR correlates with galaxy density, but what about the SF of star- forming galaxies? 12th December 2012 [email protected] The Coma supercluster (z=0.023) Coma SDSS DR7 r<17.77 (~M*+4.7 for Coma) l Around 500 sq. degrees on sky l One of the richest nearby Large-scale structures l A unique opportunity to study giant and dwarf galaxies in a variety of environments Abell 1367 Blue: Star-forming [EW(Hα) > 25Å) Red: AGN Grey: others Mahajan, Haines & Raychaudhury 2010 Green: Galaxy groups from NED 12th December 2012 [email protected] Mz<M*+1.8 Star forming: EW(Hα)> 2 Å Giants are passive irrespective of their environment Mz<M*+2.3 Contours: Galaxy density Colour-scale: SF frac%on Dwarfs are star-forming everywhere, except in the cores of clusters and groups 12th December 2012 Mahajan, Haines & Raychaudhury, 2010 [email protected] In the field, all dwarfs are forming stars Typical densi%es at 0.8<r/Rv<1.2 of Millennium groups & clusters 27,753 galaxies in 0.005<z<0.037 SDSS DR 4 90% complete to Mr=-18 Haines et al. 2007 12th December 2012 [email protected] Star formation in supercluster filaments Galaxies in filaments vs all galaxies in A study of big sample of 2dFGRS filaments, bounded by rich clusters 52 2dF filaments Dwarfs Giants 12th December 2012 [email protected] Porter et al. (2007, 2008) Clusters with at least one starburst galaxy anywhere within 3 Mpc of the centre comparison l ~100 clusters l 0.02 ≤ z ≤ 0.15 l > 6,000 bright galaxies with SDSS spectra Starburst galaxy: SFR>10 Mסּyr-1 log SFR/M* > -10.5 yr-1 • SFR declines towards the center of the cluster, but the two samples show very different behavior. • SFR in clusters with starburst galaxies is generally higher than the control clusters. • High σ, accompanied with a posi%ve skewness => a large no. of starburst galaxies are present in a narrow radial range ~1.5rvirial. 12th December 2012 Mahajan, Raychaudhury & Pimbblet, 2012 The large-scale structure of the Universe Galaxies form on filaments (alone or in a group), then travel along them to assemble into clusters cluster Fadda et al. 2008 filament 12th December 2012 Galaxy-galaxy harassment (Moore et al. 1996) • Impulsive heang caused due to interac%on between two or more galaxies • Mainly effec%ve in intermediate density environments • Causes morphological deformaon 12th December 2012 [email protected] Major mergers Antennae galaxies NGC 2207 and IC2163 • Not very important in clusters because galaxies are moving very fast • Not very important at current epoch 12th December 2012 [email protected] CL0024: Rich cluster at z=0.39 Star forming dwarfs between 1-2 Mpc from the centre Moran et al 2005 12th December 2012 [email protected] Abell 1689 (z=0.18) How do these galaxies look like? Abell 2667 (z=0.23) Cortese et al 2006 12th December 2012 [email protected] C153 in A2125 at z=0.25 Keel et al. 2004 [email protected] 12th December 2012 Does the frac%on of star-forming galaxies depend on the mass of cluster they are in? • Rich, centrally concentrated, relaxed clusters have fewer star-forming or late-type galaxies (Zabludoff & Mulchaey 1998, Biviano 1997, Mar%nez et al. 2002, Yang et al. 2005, Weinmann et al. 2006) • Tanaka et al. 2004, De Propris et al. 2004, Balogh et al. 2004 do not find any significant dependence of type-frac%on on velocity dispersion of massive groups and clusters 12th December 2012 Weinmann et al. 2006 [email protected] Starburst galaxies: Global environment Control sample Clusters with starbursts • There is no difference in cluster mass distributions (proxy: x-ray luminosity) • Velocity dispersion in clusters with starbursts is statistically higher than the comparison sample, implying they are more likely to be non-relaxed Mahajan, Raychaudhury & Pimbblet, 2012 12th December 2012 [email protected] Starburst galaxies: Local environment Most of the SB galaxies lie outside the cluster virial boundary and on filaments feeding them SB galaxies Other cluster galaxies Stas%cally, starburst galaxies are both samples found in group-like environment at 1-2r200 relave to their counterparts at similar distance from the cluster centre Mahajan, Raychaudhury & Pimbblet, 2012 12th December 2012 [email protected] Transitional galaxy population The k+A or post-starburst galaxies Coma supercluster SDSS DR6 Strong Hδ absorp%on, no Hα emission Passive k+A Star-forming Mahajan, Haines & Raychaudhury, 2011 12th December 2012 [email protected] Strong Hδ absorp%on, no Hα emission • Mz < -20 • No giant k+A giants in Coma Passive k+A Star-forming • Mean (g-r) colour for dwarfs changes by ~0.4 mag between the centre and thrice the radius of the cluster • Most k+A galaxies are found within 1.5 %mes the radius of the cluster Mahajan, Haines & Raychaudhury, 2011 12th December 2012 [email protected] Fundamental advantage over SDSS UK Schmidt telescopes have contributed immensely to the Largest superclusters at 0.03<z<0.1 study of the largest structures are in the southern hemisphere in the nearby Universe 2dFGRS survey FLAIR on UK Schmidt (40 sq. deg.) Shapley Supercluster Pisces-Cetus Supercluster Kaldare, Colless, Raychaudhury & Peterson 2003 Porter & Raychaudhury 2005 Largest superclusters at 0.03<z<0.1 are in the southern hemisphere • FLAIR Shapley-Hydra (FLASH) redshix survey with the UK Schmidt telescope • 4613 galaxies brighter than bJ=16.7 mag • 700 sq deg Kaldare, Colless, Raychaudhury & Peterson 2003 TAIPAN will have a unique opportunity to study the impact of different environments (groups, clusters, filaments) on dwarfs and giants MulFple passes in high- density regions a must 12th December 2012 [email protected] for completeness! Regarding target selec%on Galaxy stellar mass func%on itself varies with density dex Mass frac%on per Log M*/Msun Also Joss Bland-Hawthorn’s talk Low z: SDSS; Baldry et al .2006 High z: DEEP2; Bundy et al. 2006 Red galaxy frac%on depends on both local density and galaxy stellar mass SDSS Baldry et al. 2006, also Kauffmann et al. 2004 Summary • Dwarf galaxies show a stronger SFR-density relaon compared to giants. • Galaxies spend most of their %me on the cosmic-web away from clusters. When they fall in clusters, %dal forces and ram-pressure strip them of cold gas, ini%ang passive evolu%on thereaer. • SFR in infalling galaxies seems to be higher on the vicinity of clusters, especially in dynamically young clusters. • This is likely due to an increased rate of galaxy-galaxy interac%ons in intermediate environments such as the cluster outskirts. • TAIPAN has an obvious advantage for studying the impact of the large-scale cosmic web on the galaxy populaons because of the presence of several superclusters (z<0.1) in the southern hemisphere. • This work certainly requires mul%ple passes, especially for the high density regions. • Galaxy M* func%on itself is a func%on of galaxy density. 12th December 2012 [email protected] .
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