1. THE BUILD-UP OF THE COLOUR- MAGNITUDE RELATION IN LOW-Z GALAXY CLUSTERS Bertinoro School 23 th -29 th May 2009 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

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 over cosmic 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? To study 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. CMR Morphology 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. M r

8. Giant/Dwarf Ratio Mean Back Giants: M r <-20.52 Dwarfs: -20.52< M r <-18.32 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 L X No trends of g/d ratios as a function of L X 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 L X Are non BCG clusters diverse? Are BCG and X-Ray clusters similar? Downsizing Or is it?