The fraction of quiescent massive galaxies in the early Universe

¹ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio (RM), Italy e-mail: fontana@oa-roma.inaf.it
² Dipartimento di Fisica, Università di Roma “La Sapienza”, P.le A. Moro 2, 00185 Roma, Italy
³ Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003, USA
⁴ INAF – Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy

Received: 12 January 2009
Accepted: 21 January 2009

Abstract

Aims. We attempt to compile a complete, mass-selected sample of galaxies with low specific star-formation rates, and compare their properties with theoretical model predictions.

Methods. We use the  flux ratio and the SED fitting to the m spectral distribution, to select quiescent galaxies from to in the GOODS-MUSIC sample. Our observational selection can be translated into thresholds in specific star-formation rate , which can be compared with theoretical predictions.

Results. In the framework of the well-known global decline in quiescent galaxy fraction with redshift, we find that a non-negligible fraction of massive galaxies with low specific star-formation rate exists up to , including a tail of “red and dead” galaxies with  yr^-1. Theoretical models vary to a large extent in their predictions for the fraction of galaxies with low specific star-formation rates, but are unable to provide a global match to our data.