Volume 531, July 2011
|Number of page(s)||10|
|Published online||01 July 2011|
The evolution of early-type galaxies selected by their spatial clustering
Departamento de Astronomía y Astrofísica, and Centro de
Astro-IngenieríaPontificia Universidad Católica de Chile,
V. Mackenna 4860,
2 Max-Planck-Institut fur Astrophysik, Karl-Schwarzschild-Str. 1, Postfach 1317, 85741 Garching, Germany
3 Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Rd, Piscataway, NJ 08854, USA
4 Physics and Astronomy Department, Tufts University, Robinson Hall, Room 257, Medford, MA 02155, USA
Received: 18 March 2011
Accepted: 23 May 2011
Aims. We present a new method that uses luminosity or stellar mass functions combined with clustering measurements to select samples of galaxies at different redshifts likely to follow a progenitor-to-descendant relationship. Because the method uses clustering information, we refer to galaxy samples selected this way as clustering-selected samples. We apply this method to infer the number of mergers during the evolution of MUSYC early-type galaxies (ETGs) from z ≃ 1 to the present-day.
Methods. The method consists in using clustering information to infer the typical dark-matter halo mass of the hosts of the selected progenitor galaxies. Using ΛCDM predictions, it is then possible to follow these haloes to a later time where the sample of descendants will be that with the clustering of these descendant haloes.
Results. This technique shows that ETGs at a given redshift evolve into brighter galaxies at lower redshifts (considering rest-frame, passively evolved optical luminosities). This indicates that the stellar mass of these galaxies increases with time and that, in principle, a stellar mass selection at different redshifts does not provide samples of galaxies in a progenitor-descendant relationship.
Conclusions. The comparison between high-redshift ETGs and their likely descendants at z = 0 points to a higher number density for the progenitors by a factor 5.5 ± 4.0, implying the need for mergers to decrease their number density by today. Because the luminosity densities of progenitors and descendants are consistent, our results show no need for significant star-formation in ETGs since z = 1, which indicates that the needed mergers are dry, i.e. gas free.
Key words: galaxies: evolution / galaxies: formation / cosmology: observations
© ESO, 2011
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