The contribution of very massive high-redshift SWIRE galaxies to the stellar mass function
Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 3, 35122 Padova, Italy e-mail: firstname.lastname@example.org
2 Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0424, USA
3 Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312, 85741 Garching, Germany
4 Infrared Processing & Analysis Center, California Institute of Technology 100-22, Pasadena, CA 91125, USA
5 Institut d'Astrophysique de Paris, 98bis bld Arago, 75014 Paris, France
6 Astronomy Centre, CPES, University of Sussex, Falmer, Brighton BN19QJ, UK
7 INAF – Osservatorio Astronomico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
8 Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
9 INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00044 Monteporzio Catone, Italy
10 INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
11 Dipartimento di Fisica, Università degli Studi “Roma Tre”, Via della Vasca Navale 84, 00146 Roma, Italy
12 Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 2, 50125 Firenze, Italy
13 Spitzer Science Center, California Institute for Technology, 220-6, Pasadena, CA 91125, USA
Accepted: 24 September 2007
Context.In the last couple of years a population of very massive (>1011 ), high-redshift (z≥2) galaxies has been identified, but its role in galaxy evolution has not yet been fully understood.
Aims.It is necessary to perform a systematic study of high-redshift massive galaxies, in order to determine the shape of the very massive tail of the stellar mass function and determine the epoch of their assembly.
Methods.We selected high-z massive galaxies at 5.8 μm, in the SWIRE ELAIS-S1 field (1 deg2). Galaxies with the 1.6 μm stellar peak redshifted into the IRAC bands (z1-3, called “IR-peakers”) were identified. Stellar masses were derived by means of spectro-photometric fitting and used to compute the stellar mass function (MF) at z = 1-2 and 2-3. A parametric fit to the MF was performed, based on a Bayesian formalism, and the stellar mass density of massive galaxies above determined.
Results.We present the first systematic study of the very-massive tail of the galaxy stellar mass function at high redshift. A total of 326 sources were selected. The majority of these galaxies have stellar masses in excess of 1011 and lie at z > 1.5. The availability of mid-IR data turned out to be a valuable tool to constrain the contribution of young stars to galaxy SEDs, and thus their ratio. The influence of near-IR data and of the chosen stellar library on the SED fitting are also discussed. The z = 2-3 stellar mass function between 1011 and ~1012 is probed with unprecedented detail. A significant evolution is found not only for galaxies with M ~1011 , but also in the highest mass bins considered. The comoving number density of these galaxies was lower by more than a factor of 10 at z = 2-3, with respect to the local estimate. SWIRE 5.8 μm peakers more massive than 1.6 1011 provide 30-50% of the total stellar mass density in galaxies at z = 2-3.
Key words: galaxies: evolution / galaxies: luminosity function, mass function / galaxies high-redshift / galaxies: fundamental parameters / galaxies: statistics / infrared: galaxies
© ESO, 2007