The contribution of very massive high-redshift SWIRE galaxies to the stellar mass function

S. Berta; C. J. Lonsdale; M. Polletta; R. S. Savage; A. Franceschini; H. Buttery; A. Cimatti; J. Dias; C. Feruglio; F. Fiore; E. V. Held; F. La Franca; R. Maiolino; A. Marconi; I. Matute; S. J. Oliver; E. Ricciardelli; S. Rubele; N. Sacchi; D. Shupe; J. Surace

doi:doi:10.1051/0004-6361:20077491

Free access

Issue		A&A Volume 476, Number 1, December II 2007


Page(s)		151 - 175
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20077491

A&A 476, 151-175 (2007)
DOI: 10.1051/0004-6361:20077491

The contribution of very massive high-redshift SWIRE galaxies to the stellar mass function

S. Berta^{1, 2, 3}, C. J. Lonsdale^{2, 4}, M. Polletta^{2, 5}, R. S. Savage⁶, A. Franceschini¹, H. Buttery⁷, A. Cimatti⁸, J. Dias⁷, C. Feruglio⁹, F. Fiore⁹, E. V. Held¹⁰, F. La Franca¹¹, R. Maiolino⁹, A. Marconi¹², I. Matute⁷, S. J. Oliver⁶, E. Ricciardelli¹, S. Rubele¹, N. Sacchi¹¹, D. Shupe¹³, and J. Surace¹³

¹ Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 3, 35122 Padova, Italy
e-mail: berta@mpe.mpg.de
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

(Received 16 March 2007 / Accepted 24 September 2007)

Abstract
Context.In the last couple of years a population of very massive ( $M_\star$ >10¹¹ $M_\odot$ ), high-redshift (z $\ge$ 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 $\mu$ m, in the SWIRE ELAIS-S1 field (1 deg²). Galaxies with the 1.6 $\mu$ m stellar peak redshifted into the IRAC bands (z $\simeq$ 1-3, 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 z = 2 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 $M_\odot$ 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 $M_\star/L$ 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 $M_\odot$ is probed with unprecedented detail. A significant evolution is found not only for galaxies with M ~10¹¹ $M_\odot$ , 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 $\mu$ m peakers more massive than 1.6 $\times$ 10¹¹ $M_\odot$ 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

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