Searching for massive galaxies at z ≥ 3.5 in GOODS-North*
Dipartimento di Astronomia e Scienza dello Spazio, Università degli Studi di Firenze, Largo E. Fermi 3 50125 Firenze, Italy e-mail: firstname.lastname@example.org
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
Accepted: 21 January 2009
Aims. We constrain the space density and properties of massive galaxy candidates at redshifts of 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 sample was selected to mag at 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 m band to ensure that the near-IR m (rest-frame) peak is falling in or beyond this band.
Results. We found 53 candidates, of masses in the range . 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 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 . The comoving number density of galaxies with stellar masses of above 5 (a reasonable stellar-mass completeness limit for our sample) is 2.6 10-5 Mpc-3 (using the volume within ), and the corresponding stellar mass density is 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 10-5 Mpc-3 and a stellar mass density of 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 between and , and by to .
Key words: cosmology: observations / galaxies: formation / Galaxy: evolution / infrared: galaxies / galaxies: high-redshift / galaxies: photometry
© ESO, 2009