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THE BUILD-UP OF THE COLOUR-MAGNITUDE RELATION IN LOW-Z GALAXY CLUSTERS

THE BUILD-UP OF THE COLOUR-MAGNITUDE RELATION IN LOW-Z GALAXY CLUSTERS. Diego Capozzi 1,2 , Chris A. Collins 1 , John P. Stott 1. (1) Astrophysics Research Institute, Liverpool John Moores University - (2) Dep. Of Physical Sciences, Università Federico II di Napoli.

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THE BUILD-UP OF THE COLOUR-MAGNITUDE RELATION IN LOW-Z GALAXY CLUSTERS

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  1. THE BUILD-UP OF THE COLOUR-MAGNITUDE RELATION IN LOW-Z GALAXY CLUSTERS Diego Capozzi1,2, Chris A. Collins1, John P. Stott1 (1) Astrophysics Research Institute, Liverpool John Moores University - (2) Dep. Of Physical Sciences, Università Federico II di Napoli Bertinoro School 23th-29th May 2009

  2. OVERVIEW • Colour-Magnitude Relation (CMR) • Recent issues about CMR • Our work • Results • Future

  3. CMR • Interpreted as a correlation between galaxy M and mean stellar Z • Alternatively as due to a change of the mean age • age-metallicity degeneracy • Its origin can be explained through: • concurrent formation of Es in CCs in high-z monolithic collapse (Kodama & Arimoto 1997) • hierarchical formation of Es via merging overcosmic time (Kauffmann & Charlot 1998)

  4. CMR • Does its morphology evolve with z? • Slope: measures differential properties of Es as a function of L • Zero-point: for high-z (z >0.6) clusters it’s a measure of the formation epoch of the dominant stellar population of Es

  5. Recently • Analysis of CMR build-up and its relation with environment has provided: • clues to Es downsizing as • function of redshift • function of environment De Lucia et al. (2005)

  6. What do we want to do? • Tostudy the evolution of early-type galaxies in galaxy clusters • Low-z (0.05<z<0.26) • Optically (~500 maxBCG+HMF) and X-Ray (97 XCS) selected clusters • Using SDSS DR6 data

  7. Galaxies with R<1 Mpc Iterative biweight fit Bootstrap for determining errors on slope and zero-point Some differences among cluster samples seen Interpretation: work in progress g-r vs. Mr CMR Morphology

  8. Giant/Dwarf Ratio Giants: Mr<-20.52 Dwarfs: -20.52< Mr<-18.32 Mean Back Local Background: 2<R<3 Mpc Mean Background: Average among 17 control regions Best fit line: only statistical samples used Our results consistent with De Lucia et al. (2007) values for SDSS clusters

  9. G/D ratios vs LX No trends of g/d ratios as a function of LX have been found

  10. Results & Discussion • We analysed clusters galaxy evolution at low-z • Optically and X-Ray selected samples used • Some differences on the CMR morphology among the samples • Our g/d ratios are in accordance with De Lucia et al. (2007) values for SDSS clusters • No dependence of g/d ratios on LX • Are non BCG clusters diverse? Are BCG and X-Ray clusters similar? Downsizing Or is it?

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