The Stellar Mass Assembly of Galaxies fromz= 0 toz= 4: Analysis of a Sample Selected in the Rest‐Frame Near‐Infrared withSpitzer

Abstract

Using a sample of ∼28,000 sources selected at 3.6-4.5 microns with Spitzer observations of the HDF-N, the CDF-S, and the Lockman Hole (surveyed area: ∼664 arcmin 2 ), we study the evolution of the stellar mass content of the Universe at 0<z<4. We calculate stellar masses and photometric redshifts, based on ∼2,000 templates built with stellar population and dust emission models fitting the UV-to-MIR spectral energy distributions of galaxies with spectroscopic redshifts. We estimate stellar mass functions for different redshift intervals. We find that 50% of the local stellar mass density was assembled at 0<z<1 (average SFR: 0.048 M ⊙ yr −1 Mpc −3 ), and at least another 40% at 1<z<4 (average SFR: 0.074 M ⊙ yr −1 Mpc −3 ). Our results confirm and quantify the "downsizing" scenario of galaxy formation. The most massive galaxies (M>10 12.0 M ⊙ ) assembled the bulk of their stellar content rapidly (in 1-2 Gyr) beyond z∼3 in very intense star formation events (producing high specific SFRs). Galaxies with 10 11.5 <M<10 12.0 M ⊙ assembled half of their stellar mass before z∼1.5, and more than 90% of their mass was already in place at z∼0.6. Galaxies with M<10 11.5 M ⊙ evolved more slowly (presenting smaller specific SFRs), assembling half of their stellar mass below z∼1. About 40% of the local stellar mass density of 10 9.0 <M<10 11.0 M ⊙ galaxies was assembled below z∼0.4, most probably through accretion of small satellites producing little star formation. The cosmic stellar mass density at z>2.5 is dominated by optically faint (R 25) red galaxies (Distant Red Galaxies or BzK sources) which account for ∼30% of the global population of galaxies, but contribute at least 60% to the cosmic stellar mass density. Bluer galaxies (e.g., Lyman Break Galaxies) are more numerous but less massive, contributing less than 50% to the global stellar mass density at high redshift.

The Galaxy UV Luminosity Function Before the Epoch of Reionization

“…We find good agreement with observations (Pérez- González et al 2008;Stark et al 2013;Tomczak et al 2014;Grazian et al 2015;Song et al 2015) taking into account the scatter in observations at z < 2, and the uncertain but potentially significant contribution of massive quiescent galaxies at low redshift. (2015); Song et al (2015).…”

Mass-metallicity relation explored with CALIFA

“…Matteucci & Francois 1989;Boissier & Prantzos 1999), combined with the fact that more massive regions form stars faster (i.e., at higher SFRs), thus earlier in cosmological times, which can be considered a local downsizing effect, similar to the one observed in individual galaxies (e.g. Pérez-González et al 2008). This explanation does not require a strong effect of inflows/outflows in shaping the M-Z relation, which can be naturally explained by secular evolution processes.…”

Dusty star-forming galaxies at high redshift

“…This however assumes that high-J CO transitions trace the same region as low-J CO lines, however this often cannot be the case as the integrated SMG star formation history would exceed the local baryon density . Similarly, potential discrepancies in the integrated cosmic star formation history, and evolution of the stellar mass function may imply either a bottom light or top heavy IMF at high-z, with the idea that such an IMF would cause inferred SFRs to decrease, and bring the two values into agreement (Hopkins & Beacom, 2006;Elsner et al, 2008;Pérez-González et al, 2008;Wilkins et al, 2008), though issues related to luminosity function integration as well as nebular line contamination in stellar mass estimates may relieve some of these tensions (Reddy & Steidel, 2009;Stark et al, 2013). van Dokkum (2008 suggested that the color evolution of early type galaxies at z ∼ 1, combined with their mass to light ratios may be well described by a bottom light IMF, though note in van Dokkum & Conroy (2012) that the same observations could be consistent with a Salpeter IMF.…”