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Issue A&A
Volume 500, Number 2, June III 2009
Page(s) 705 - 723
Section Extragalactic astronomy
DOI 10.1051/0004-6361/200810630
Published online 19 March 2009

A&A 500, 705-723 (2009)
DOI: 10.1051/0004-6361/200810630

Searching for massive galaxies at z $\geq$ 3.5 in GOODS-North

C. Mancini1, 2, 3, I. Matute2, A. Cimatti4, E. Daddi3, M. Dickinson5, G. Rodighiero6, M. Bolzonella7, and L. Pozzetti7

1  Dipartimento di Astronomia e Scienza dello Spazio, Università degli Studi di Firenze, Largo E. Fermi 3 50125 Firenze, Italy
    e-mail: mancini@arcetri.astro.it
2  Osservatorio Astrofisico di Arcetri (OAF), INAF-Firenze, Largo E. Fermi 5, 50125 Firenze, Italy
3  CEA-Saclay,DSM/DAPNIA/Service d'Astrophysique, 91191 Gif-Sur Yvette Cedex, France
4  Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
5  NOAO, 950 N. Cherry Ave. PO 26732, Tucson, AZ 85726-6732, USA
6  Dipartimento di Astronomia, Università di Padova, Vicolo Osservatorio 2, 35122 Padova, Italy
7  INAF-Bologna, via Ranzani, 40127 Bologna, Italy

Received 17 July 2008 / Accepted 21 January 2009

Abstract
Aims. We constrain the space density and properties of massive galaxy candidates at redshifts of $z\geq3.5$ in the Great Observatories Origin Deep Survey North (GOODS-N) field. By selecting sources in the Spitzer + IRAC bands, a sample highly complete in stellar-mass is assembled, including massive galaxies that are very faint in the optical/near-IR bands and would be missed by samples selected at shorter wavelengths.
Methods. The $z\geq3.5$ sample was selected to $m_{\rm AB}=23$ mag at $4.5~\mu$m using photometric redshifts obtained by fitting the galaxies spectral energy distribution at optical, near-IR bands, and IRAC bands. We also require that the brightest band (in AB scale) in which candidates are detected is the IRAC $8.0~\mu$m band to ensure that the near-IR $1.6~\mu$m (rest-frame) peak is falling in or beyond this band.
Results. We found 53 $z~\geq3.5$ candidates, of masses in the range $M_{\star}\sim10^{-}10^~M_{\odot}$. At least ~81% of these galaxies are missed by traditional Lyman Break selection methods based on ultraviolet light. Spitzer + MIPS emission is detected for 60% of the sample of $z\geq3.5$ galaxy candidates. Although in some cases this might suggest a residual contamination from lower redshift star-forming galaxies or Active Galactic Nuclei, 37% of these objects are also detected in the sub-mm/mm bands in SCUBA, AzTEC, and MAMBO surveys, and have properties fully consistent with vigorous starburst galaxies at $z\geq3.5$. The comoving number density of galaxies with stellar masses of above 5 $\times$ $10^~M_{\odot}$ (a reasonable stellar-mass completeness limit for our sample) is 2.6 $\times$ 10-5 Mpc-3 (using the volume within 3.5<z<5), and the corresponding stellar mass density is ${\sim}(2.9\pm 1.5)$ $\times$ $10^6~M_{\odot}$ Mpc-3, or about 3% of the local density above the same stellar mass limit. For the subsample of MIPS-undetected galaxies, we measure a number density of ${\sim}0.97$ $\times$ 10-5 Mpc-3 and a stellar mass density of ${\sim}(1.15\pm 0.7)$ $\times$ $10^6~M_{\odot}$ Mpc-3. Even in the unlikely case that these are all truly quiescent galaxies, this would imply an increase in the space density of passive galaxies by a factor of ${\sim}15$ between $z\sim 4$ and z=2, and by ${\sim}100$ to z=0.


Key words: cosmology: observations -- galaxies: formation -- Galaxy: evolution -- infrared: galaxies -- galaxies: high-redshift -- galaxies: photometry



© ESO 2009


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