Satellites around massive galaxies since z∼ 2

© 2012 The Authors. © 2012 Monthly Notices of the Royal Astronomical Society © 2012 RAS. We thank the anonymous referee for a careful and constructive reading of the manuscript that helped us to improve the quality of the paper. We are grateful to Lulu Liu for providing us with their measurements of the fraction of galaxies with satellites obtained from the SDSS, used here as a local (z = 0) comparison. We thank Juan Betancort for his valuable input on several aspects of the statistical analysis in this paper. We are grateful to Sergio Pascual for his very useful help with programming questions. We would like also to acknowledge fruitful discussions with Javier Cenarro, Luis Díaz, Rosa Domínguez, César González, Carlos López San Juan, José Onorbe, Thorsten Naab and Vicent Quilis. IT is a Ramón y Cajal Fellow of the Spanish Ministry of Science and Innovation. This work has been supported by the 'Programa Nacional de Astronomía y Astrofísica' of the Spanish Ministry of Science and Innovation under grant AYA2010-21322-C03-02. PGP and GB acknowledge support from the Spanish Programa Nacional de Astronomía y Astrofísica under grants AYA2009-10368 and AYA2009-07723-E. This work has made use of the Rainbow Cosmological Surveys Data base, which is operated by the Universidad Complutense de Madrid (UCM).
The accretion of minor satellites has been postulated as the most likely mechanism to explain the significant size evolution of massive galaxies over cosmic time. Using a sample of 629 massive (M_star~ 10^11 M_⊙) galaxies from the near-infrared Palomar/DEEP-2 survey, we explore what fraction of these objects have satellites with 0.01 < M_sat/M_central < 1 (1:100) up to z= 1 and what fraction have satellites with 0.1 < M_sat/M_central < 1 (1:10) up to z= 2 within a projected radial distance of 100 kpc. We find that the fraction of massive galaxies with satellites, after background correction, remains basically constant and close to 30 per cent for satellites with a mass ratio down to 1:100 up to z= 1, and close to 15 per cent for satellites with a 1:10 mass ratio up to z= 2. The family of spheroid-like massive galaxies presents a 2–3 times larger fraction of objects with satellites than the group of disc-like massive galaxies. A crude estimation of the number of 1:3 mergers a massive spheroid-like galaxy has experienced since z~2 is around 2. For a disc-like galaxy this number decreases to ~1.
Ministerio de Ciencia e Innovación (MICINN)
Programa Nacional de Astronomía y Astrofísica (PNAyA), España
Depto. de Física de la Tierra y Astrofísica
Fac. de Ciencias Físicas
TRUE
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