Must Starforming Galaxies Rapidly Get Denser Before They Quench?


الملخص بالإنكليزية

Using the deepest data yet obtained, we find no evidence preferring compaction-triggered quenching---where rapid increases in galaxy density truncate star formation---over a null hypothesis in which galaxies age at constant surface density ($Sigma_eequiv M_*/2pi r_{e}^{2}$). Results from two fully empirical analyses and one quenching-free model calculation support this claim at all $zleq3$: (1) Qualitatively, galaxies mean $U-V$ colors at $6.5lesssimlogSigma_e/{rm M_odot},{rm kpc}^{-2}lesssim10$ have reddened at rates/times correlated with $Sigma_e$, implying that there is no density threshold at which galaxies turn red but that $Sigma_e$ sets the pace of maturation; (2) Quantitatively, the abundance of $log M_*/{rm M_odot}geq9.4$ red galaxies never exceeds that of the total population a quenching time earlier at any $Sigma_e$, implying that galaxies need not transit from low to high densities before quenching; (3) Applying $dlog r_{e}/dt =1/2,dlog M_*/dt$ to a suite of lognormal star formation histories reproduces the evolution of the size--mass relation at $log M_*geq10$. All results are consistent with evolutionary rates being set ab initio by global densities, with denser objects evolving faster than less-dense ones towards a terminal quiescence induced by gas depletion or other $sim$Hubble-timescale phenomena. Unless stellar ages demand otherwise, observed $Sigma_e$ thresholds need not bear any physical relation to quenching beyond this intrinsic density--formation epoch correlation, adding to Lilly & Carollos arguments to that effect.

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