Morphological Quenching of Star Formation: Making Early-Type Galaxies Red

Abstract

We point out a natural mechanism for quenching of star formation in early-type galaxies (ETGs). It automatically links the color of a galaxy with its morphology and does not require gas consumption, removal or termination of gas supply. Given that star formation takes place in gravitationally unstable gas disks, it can be quenched when a disk becomes stable against fragmentation to bound clumps. This can result from the growth of a stellar spheroid, for instance by mergers. We present the concept of morphological quenching (MQ) using standard disk instability analysis, and demonstrate its natural occurrence in a cosmological simulation using an efficient zoom-in technique. We show that the transition from a stellar disk to a spheroid can be sufficient to stabilize the gas disk, quench star formation, and turn an ETG red and dead while gas accretion continues. The turbulence necessary for disk stability can be stirred up by sheared perturbations within the disk in the absence of bound star-forming clumps. While other quenching mechanisms, such as gas stripping, active galactic nucleus feedback, virial shock heating, and gravitational heating are limited to massive halos, MQ can explain the appearance of red ETGs also in halos less massive than ∼1012 M . The dense gas disks observed in some of today's red ellipticals may be the relics of this mechanism, whereas red galaxies with quenched gas disks could be more frequent at high redshift.

Galaxy Growth at Early Times from 3D Studies

“…These properties, along with trends of increasing central dynamical mass fraction and bulge-to-disk ratio with galaxy mass and evolutionary stage, and possibly older clump ages at smaller galactocentric distances (e.g., Genzel et al 2008Genzel et al , 2011Förster Schreiber et al 2011b;Wuyts et al 2012;Tacchella et al 2014), are consistent with theoretical arguments and numerical simulations of turbulent gas-rich disks in which giant star-forming clumps result from violent gravitational instabilities and bulges form via efficient secular processes on timescales < 1 Gyr (e.g., Bournaud et al 2007Bournaud et al , 2014Ceverino et al 2012;Dekel & Burkert 2014). Bulge growth in high-z disks can lead to "morphological quenching" as the central stellar spheroidal component stabilizes the gas-rich disk against fragmentation (e.g., Martig et al 2009). Dynamical analysis of the SINS/zC-SINF AO sample revealed increasingly centrally peaked Toomre Q values well above unity in the inner 2 − 3 kpc of the most massive galaxies, where star formation is suppressed and a massive stellar bulge is present -tantalizing evidence for inside-out gravitationally-driven quenching acting at z ∼ 2 (Genzel et al 2014a).…”

SDSS-IV MaNGA-resolved Star Formation and Molecular Gas Properties of Green Valley Galaxies: A First Look with ALMA and MaNGA

“…On the other hand, although the morphological quenching (Martig et al 2009) also predicts low SFE in the disks that are stabilized against gas fragmentation due to the presence of massive bulges, it may not be relevant to the three systems discussed in this work since morphological quenching is only effective in bulge dominated systems, unlike our green valley galaxies.…”

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

“…For massive galaxies, morphological quenching is one of the important processes, which can quench star formation even in the presence of a gas component. Martig et al (2009) showed that star formation is suppressed once the central spheroidal component becomes sufficiently massive to stabilise the galactic disc against local gravitational instability. Some observational studies suggested that morphological quenching is in action in the earlytype galaxies (Martig et al 2013;Morokuma-Matsui et al 2015).…”