The ATLAS3D Project - XXVIII. Dynamically-driven star formation
  suppression in early-type galaxies
  We present measurements of the star formation rate (SFR) in the early-type
galaxies (ETGs) of the ATLAS3D sample, based on Wide-field Infrared Survey
Explorer (WISE) 22um and Galaxy Evolution Explorer (GALEX) far-ultraviolet
emission. We combine these with gas masses estimated from 12CO and HI data in
order to investigate the star formation efficiency (SFE) in a larger sample of
ETGs than previously available. We first recalibrate (based on WISE data) the
relation between old stellar populations (traced at Ks-band) and 22um
luminosity, allowing us to remove the contribution of 22um emission from
circumstellar dust. We then go on to investigate the position of ETGs on the
Kennicutt-Schmidt (KS) relation. Molecular gas-rich ETGs have comparable star
formation surface densities to normal spiral galaxy centres, but they lie
systematically offset from the KS relation, having lower star formation
efficiencies by a factor of ~2.5 (in agreement with other authors). This effect
is driven by galaxies where a substantial fraction of the molecular material is
in the rising part of the rotation curve, and shear is high. We show here for
the first time that although the number of stars formed per unit gas mass per
unit time is lower in ETGs, it seems that the amount of stars formed per
free-fall time is approximately constant. The scatter around this dynamical
relation still correlates with galaxy properties such as the shape of the
potential in the inner regions. This leads us to suggest that dynamical
properties (such as shear or the global stability of the gas) may be important
second parameters that regulate star formation and cause much of the scatter
around star-formation relations.
