http://arxiv.org/abs/1608.07577
Using the deepest space-based data obtained, we find that a scenario wherein galaxy star formation is quenched by crossing a high stellar mass surface density ($\Sigma_e\equiv M_*/2\pi r_{e}^{2}$) threshold is not favored over a null case where evolution from blue to red occurs at roughly fixed $\Sigma_e$. Two observations support this: (1) The mean $U-V$ colors of galaxies at all $6.5\lesssim\log\Sigma_e/M_\odot\,{\rm kpc}^{-2}\lesssim10$ have reddened since $z\approx3$ at rates/times correlated with $\Sigma_e$, i.e., there is no preferred surface density at which blue galaxies become red, but $\Sigma_e$ controls the pace of maturation. (2) The growth of the number of $\log M_*/M_\odot\geq 9.4$ red galaxies at fixed $\Sigma_e$ shows no significant enhancement over that of the global population at $0.2\leq z\leq3.0$ ($\Delta t\approx9$ Gyr), i.e., the $\gtrsim2.5\times$ rise in the red fraction over that interval need not be due to blue galaxies rapidly transforming en masse from low to high densities, but is accounted for by the general “turning-red” of all galaxies at all $\Sigma_e$. These results are consistent with a scenario wherein evolutionary rates are set ab initio by primordial overdensities, with denser objects evolving faster than less-dense ones towards a terminal quiescence induced by gas depletion or other Hubble-timescale phenomena. Unless ruled-out by stellar ages, observed $\Sigma_e$ thresholds are thus as likely to be consequences of density-accelerated evolution as they are causes of quenching.
L. Abramson and T. Morishita
Tue, 30 Aug 16
38/78
Comments: 6 pages, 3 figures, submitted to ApJ Letters
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