GALAXY STELLAR MASS ASSEMBLY BETWEEN 0.2 <z< 2 FROM THE S-COSMOS SURVEY

Abstract

We follow the galaxy stellar mass assembly by morphological and spectral type in the COSMOS 2 deg 2 field. We derive the stellar mass functions and stellar mass densities from z = 2 to z = 0.2 using 196,000 galaxies selected at F 3.6 μm > 1 μJy with accurate photometric redshifts (σ (z phot −z spec )/(1+z spec ) = 0.008 at i + < 22.5). Using a spectral classification, we find that z ∼ 1 is an epoch of transition in the stellar mass assembly of quiescent galaxies. Their stellar mass density increases by 1.1 dex between z = 1.5-2 and z = 0.8-1 (Δt ∼ 2.5 Gyr), but only by 0.3 dex between z = 0.8-1 and z ∼ 0.1 (Δt ∼ 6 Gyr). Then, we add the morphological information and find that 80%-90% of the massive quiescent galaxies (log M ∼ 11) have an elliptical morphology at z < 0.8. Therefore, a dominant mechanism links the shutdown of star formation and the acquisition of an elliptical morphology in massive galaxies. Still, a significant fraction of quiescent galaxies present a Spi/Irr morphology at low mass (40%-60% at log M ∼ 9.5), but this fraction is smaller than predicted by semi-analytical models using a "halo quenching" recipe. We also analyze the evolution of star-forming galaxies and split them into "intermediate activity" and "high activity" galaxies. We find that the most massive "high activity" galaxies end their high star formation rate phase first. Finally, the space density of massive star-forming galaxies becomes lower than the space density of massive elliptical galaxies at z < 1. As a consequence, the rate of "wet mergers" involved in the formation of the most massive ellipticals must decline very rapidly at z < 1, which could explain the observed slow down in the assembly of these quiescent and massive sources.

Star formation properties of sub-mJy radio sources

“…Passive galaxies are the vast majority of RL AGN hosts at masses > 10 10.5 M⊙ while at lower masses they are mostly MS galaxies. This trend is similar to what is observed in the overall galaxy population; the fraction of active galaxies increases as the stellar mass decreases (e.g., Peng et al 2010;Ilbert et al 2010Ilbert et al , 2013. Therefore, it seems that there is no strong connection between the presence of radio jets and the SF activity of the host.…”

“…This reflects the fact that the SFR is well constrained when FIR photometry is available, while on the stellar masses there are larger uncertainties, especially in AGN host galaxies, depending on the fitting technique and especially on the model library adopted (e.g. Ilbert et al 2010). …”

Redshift evolution of stellar mass versus gas fraction relation in 0 <z< 2 regime: observational constraint for galaxy formation models

“…Here, we mention that Popping et al (2012) showed that their IAB < 24 mag sample is complete (100 %) for the range of 10 9.2 M⊙ < M⋆ < 10 11.7 M⊙ at 0.5 < z < 0.75 with respect to the SMF derived in the same field (Ilbert et al 2010). However, it is almost evenly < 50% for all stellar mass ranges at z > 1.25.…”

Comparing Dark Energy Survey andHST–CLASH observations of the galaxy cluster RXC J2248.7−4431: implications for stellar mass versus dark matter

“…We chose to use LEPHARE, together with the Bruzual & Charlot (2003) templates, as this combination has been shown to be robust in the estimation of physical parameters of galaxies (Ilbert et al 2010).…”