The Build-up of the Red Sequence in High Redshift Galaxy Clusters Pierluigi Cerulo Presented in fulfillment of the requirements of the degree of Doctor of Philosophy 12 February 2015 Faculty of Science, Engineering and Technology Swinburne University i Abstract The primary scientific goal of this thesis is to study of the evolution of galaxies in high redshift clusters through the investigation of the build-up of the red sequence as a function of redshift. We address this problem from four complementary points of view, namely the study of the build-up of the faint end of the red sequence, the analysis of the morphology of red sequence galaxies, the investigation of the relationships between galaxy stellar populations, luminosity, and morphology, and the comparison between the properties of galaxies in low and high mass clusters. For this purpose we use a sample of 9 galaxy clusters at 0:8 < z < 1:5 from the HAWK- I Cluster Survey (HCS, Lidman et al. 2013), a program conducted with the infrared High Acuity Wide-field K-band Imager (HAWK-I) at the ESO Very Large Telescope (VLT), and aimed at the study of high-redshift clusters. Deep optical imaging from the Hubble Space Telescope (HST) and VLT, and up to 100 redshifts from various observing programs are also available for each of the clusters, making the HCS one of the richest and deepest samples of high redshift clusters currently available. Throughout the thesis we use the WIde-field Nearby Galaxy-cluster Survey (WINGS, Fasano et al. 2006) as a comparison sample of clusters at low redshifts. Given the diversity and heterogeneity of the HCS dataset, we set out, at the beginning of this project, to develop a method for the analysis of the clusters with the aim of using all the available photometric and spectroscopic information to produce unbiased multi-wavelength samples. We tested our method on the cluster XMMU J1229+0151, at z = 0:98, which is one of the lowest-redshift HCS clusters and has one of the richest datasets. We implemented two methods for the estimation of cluster membership, based on photometric redshifts and on statistical background subtraction, showing that they produced reliable and consistent results. We also adopted a coupled visual and automatic approach for the morphological classification of red sequence galaxies, showing that it results in a reliable separation between elliptical and S0 galaxies, as well as disc-dominated galaxies. The analysis of the HCS clusters shows that the red sequence was already in place at z = 1:5. In fact, we find that the red sequence slope and intrinsic scatter do not change significantly with redshift, in agreement with most results in the recent literature. We also find that the cluster red sequence was already developed at low luminosities, showing that the luminous-to-faint-ratio and the luminosity distributions are consistent with the z 0:05 clusters of the WINGS survey. Interestingly, we detect a population of ∼ ii luminous (VAB < 22:0 mag) and massive (log(M∗=M ) > 11:0) red sequence galaxies − at the centres of the clusters with high dark matter halo masses which are not present in low-mass clusters. In order to explain the properties of the HCS red sequence, we propose an evolutionary scenario based on the accretion of low-mass groups on to a central massive protocluster at z > 2. According to this scenario, the red sequence is populated both by the galaxies that ceased their star formation in the protocluster and by the galaxies that had their star formation quenched in the satellite groups. The latter populate the red sequence at all stellar masses, resulting in a fast build-up also at the faint end, as we observe in the HCS clusters. In this scenario, more massive clusters are formed at earlier times, with respect to their low-mass counterparts, and accrete satellite groups over longer timescales. Therefore, the central galaxies in these systems accrete low-mass satellite galaxies over longer timescales than those involved in lower-mass clusters, experiencing a higher mass growth. This can explain the presence of the high mass central galaxies in the most massive clusters. As well as analyse the evolution of the cluster red sequence, we investigate the mor- phological properties of red sequence members. We find that the HCS red sequence is dominated by early-type galaxies as in lower-redshift clusters. However , the comparison with WINGS shows that there is a significant growth in the fraction of S0 galaxies, which become dominant on the WINGS red sequence at magnitudes VAB > 21:0 mag. Unlike − WINGS, the HCS red sequence is dominated by elliptical galaxies at all luminosities and stellar masses. We conclude that elliptical and S0 galaxies follow different evolutionary paths, and that the low-redshift S0s were formed as the result of the morphological trans- formation of quiescent spiral galaxies. We also find that, at both high and low redshifts, late-type galaxies make up 10% of the red sequence, and that they have slightly bluer colours than early-type galaxies. Our analysis also shows that the bright end of the red sequence is dominated by elliptical galaxies at low and high redshifts. In order to study the relationships between galaxy luminosity, morphology, and stellar populations, we analysed a sample of spectra of red sequence galaxies in 3 HCS clusters at z 1 observed at the 8m Gemini-North telescope and at the 10m Keck I telescope. ∼ The preliminary results of this study, which are based on a purely qualitative analysis of the co-added spectra, suggest that S0 galaxies host younger stellar populations than those of elliptical galaxies. Our results also suggest that the age of the stellar populations increases with galaxy luminosity. We stress that these results are preliminary and that only after estimating stellar age and metallicity from the available spectra, we will be able to quantitatively investigate any relation between stellar populations, morphology, and iii luminosity of red sequence galaxies. iv v Acknowledgements I would like to thank my supervisors Warrick Couch and Chris Lidman who gave me the opportunity to work on an exciting research project for my PhD. I would also like to thank the Australian Astronomical Observatory (AAO) for granting me a top-up scholarship and for hosting me during my visits. I thank the AAO staff for their help and assistance during my visits at the observatory. The research developed during my PhD would not have been possible without the help and support of the HCS collaboration who gave me useful feedback and comments for my paper \The morphological transformation of red sequence galaxies in the distant cluster XMMU J1229+0151". In particular, I thank Simona Mei and Marc-Huertas-Company who hosted me at the Paris Observatory, allowing me to actively participate in their research activities, and giving me valuable suggestions for my work. I would also like to thank Ricardo Demarco and Julie Nantais for providing me with the most up to date redshift catalogues for the cluster RDCS J1252.9-2927, which have improved the quality and reliability of my results. I thank the members of external collaborations who provided me with additional data, catalogues, and software. The SofI images of the cluster XMMU J1229+0151 were pro- vided by Joana Santos. The ISAAC images of the clusters RCS 2319.8+0038, RCS 0220.9- 0333, and RCS 2345-3633 were provided by Roberto Mu~noz.The WINGS catalogues and additional related information were provided by Bianca Poggianti and Alessia Moretti. The software for stellar population measurements was provided by Max Spolaor and Pe- ter Jensen. The software for simulating galaxy images was provided by Boris H¨außler. I thank Evelyn Caris for her help with the CarPy software and Keck data reduction. I thank Joshua Meyers for kindly providing his PSF fitting software. Finally I would like to thank the Centre for Astrophysics and Supercomputing for giving me the opportunity to work in a high quality research centre with an excellent work environment. In particular, I thank my review panel for their helpful suggestions and the PhD student coordinators Chris Blake and Virginia Kilborn for the useful meetings organised in these four years. I also thank Chris Blake, Darren Croton, Alister Graham, and Luca Cortese for their suggestions on the estimation of completeness limits, red sequence number counts, aperture photometry, and red sequence selection effects, and I thank Matt Owers and Max Spolaor for introducing me to MOS spectroscopy and stellar populations. The work presented in this thesis has been carried out with the Green and gSTAR vi supercomputers, and I thank the Swinburne supercomputing team for their support. vii ix Statement of originality The work presented in this thesis was carried out at the Centre for Astrophysics & Supercomputing of the Swinburne University of Technology and at the Australian Astro- nomical Observatory during the period 2010-2015. This thesis contains no material that has been accepted for the award of any other degree or diploma. To the best of my knowledge, this thesis contains no material previously published or written by another author, except where due reference is made in the text of the thesis. All figures were created by the author, except where due reference is made in the text of the thesis. All work presented is that of the author, except where due reference is made in the text of the thesis and I remain solely responsible for this work. All my principal and associate supervisors were co-authors of the relevant publications during which I received their guidance and input. The content of the Chapters listed below has appeared in refereed journals.