Abstract
We present a comparison between the observed color distribution, number and mass density of massive galaxies at 1.5 4x10^10 Msun) galaxies extracted from the FIRES, GOODS-South, and MUSYC surveys, together spanning an area of 496 arcmin^2, with synthetic photometry from hydrodynamical merger simulations. As in the Hopkins et al. (2006b) model, we use the observed quasar luminosity function to estimate the merger rate. We find that the synthetic U-V and V-J colors of galaxies that had a quasar phase in their past match the colors of observed galaxies that are best characterized by a quiescent stellar population. At z ~ 2.6, the observed number and mass density of quiescent red galaxies with M > 4x10^10 Msun is consistent with the model in which every quiescent massive galaxy underwent a quasar phase in the past. At z ~ 1.9, 2.8 times less quiescent galaxies are observed than predicted by the model as descendants of higher redshift quasars. The merger model also predicts a large number of galaxies undergoing merger-driven star formation. We find that the predicted number and mass density accounts for 30-50% of the observed massive star-forming galaxies. However, their colors do not match those of observed star-forming galaxies. In particular, the colors of dusty red galaxies are not reproduced by the simulations. Several possible origins of this discrepancy are discussed. The observational constraints on the validity of the model are currently limited by cosmic variance and uncertainties in stellar population synthesis and radiative transfer.
Highlights
In recent years, deep near- and mid-infrared observations have revealed significant populations of red galaxies at redshifts z ∼ 2 and above (Franx et al 2003; Daddi et al 2004; Yan et al 2004)
We find that the synthetic U − V and V − J colors of galaxies that had a quasar phase in their past match the colors of observed galaxies that are best characterized by a quiescent stellar population
Given that M05-based synthetic photometry placed some of the simulated post-quasar galaxies with low sSFRs in the star-forming part of the UVJ diagram, we focus on the results obtained using BC03 templates
Summary
Deep near- and mid-infrared observations have revealed significant populations of red galaxies at redshifts z ∼ 2 and above (Franx et al 2003; Daddi et al 2004; Yan et al 2004). 4 MPE, Giessenbackstrasse, D-85748, Garching, Germany 5 Department of Astronomy, University of California Berkeley, Berkeley, CA 94720 6 Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101; Hubble Fellow 7 Department of Astronomy, Yale University, New Haven CT 06520-8101 8 Kavli Institute for Cosmological Physics, and Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 9 Enrico Fermi Institute, Chicago, IL 60637; Spitzer Fellow Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vei 30, DK-2100 Copenhagen, Denmark European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei Munchen, Germany masses, Wuyts et al (2007) found that the lower mass galaxies at redshifts 2 < z < 3.5 have bluer rest-frame U − V colors compared to the most massive galaxies. A substantial fraction of the massive red galaxies at high redshift are best characterized by a quiescent stellar population on the basis of their broad-band SEDs (Labbe et al 2005; Wuyts et al 2007) and the presence of a Balmer/4000 ̊A break and absence of emission lines in their rest-frame optical spectra (Kriek et al 2006)
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