Astronomy and Astrophysics, volume 500, 705-723 (2009/6-3)
Searching for massive galaxies at z ≥ 3.5 in GOODS-North.
MANCINI C., MATUTE I., CIMATTI A., DADDI E., DICKINSON M., RODIGHIERO G., BOLZONELLA M. and POZZETTI L.
Abstract (from CDS):
We constrain the space density and properties of massive galaxy candidates at redshifts of z≥3.5 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. The z≥3.5 sample was selected to mAB=23mag at 4.5µm 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 8.0µm band to ensure that the near-IR 1.6µm (rest-frame) peak is falling in or beyond this band. We found 53 z≥3.5 candidates, of masses in the range M*∼1010-1011M☉. 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≥3.5 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≥3.5. The comoving number density of galaxies with stellar masses of above 5x1010 M☉ (a reasonable stellar-mass completeness limit for our sample) is 2.6x10–5/Mpc3 (using the volume within 3.5<z<5), and the corresponding stellar mass density is ~(2.9±1.5)x106M☉/Mpc3, 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 ∼0.97x10–5Mpc–3 and a stellar mass density of ~(1.15±0.7)x106M☉/Mpc3. 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 ∼15 between z∼4 and z=2, and by ∼100 to z=0.
cosmology: observations - galaxies: formation - Galaxy: evolution - infrared: galaxies - galaxies: high-redshift - galaxies: photometry
Table 6: [MMC2009c] NNNNN N=53 among (Nos 522-15771).
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