Abstract
Observations show a prevalence of high redshift galaxies with large stellar
masses and predominantly passive stellar populations. A variety of processes
have been suggested that could reduce the star formation in such galaxies to
observed levels, including quasar mode feedback, virial shock heating, or
galactic winds driven by stellar feedback. However, the main quenching
mechanisms have yet to be identified. Here we study the origin of star
formation quenching using Argo, a cosmological zoom-in simulation that follows
the evolution of a massive galaxy at $z\geq2$. This simulation adopts the
same sub-grid recipes of the Eris simulations, which have been shown to form
realistic disk galaxies, and, in one version, adopts also a mass and spatial
resolution identical to Eris. The resulting galaxy has properties consistent
with those of observed, massive (M_* ~ 1e11 M_sun) galaxies at z~2 and with
abundance matching predictions. Our models do not include AGN feedback
indicating that supermassive black holes likely play a subordinate role in
determining masses and sizes of massive galaxies at high z. The specific star
formation rate (sSFR) of the simulated galaxy matches the observed M_* - sSFR
relation at early times. This period of smooth stellar mass growth comes to a
sudden halt at z=3.5 when the sSFR drops by almost an order of magnitude within
a few hundred Myr. The suppression is initiated by a leveling off and a
subsequent reduction of the cool gas accretion rate onto the galaxy, and not by
feedback processes. This "cosmological starvation" occurs as the parent dark
matter halo switches from a fast collapsing mode to a slow accretion mode.
Additional mechanisms, such as perhaps radio mode feedback from an AGN, are
needed to quench any residual star formation of the galaxy and to maintain a
low sSFR until the present time.
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