The SAMI Galaxy Survey: Kinematics of Dusty Early-Type Galaxies
  Recently, large samples of visually classified early-type galaxies (ETGs)
containing dust have been identified using space-based infrared observations
with the Herschel Space Telescope. The presence of large quantities of dust in
massive ETGs is peculiar as X-ray halos of these galaxies are expected to
destroy dust in 10 Myr (or less). This has sparked a debate regarding the
origin of the dust: is it internally produced by asymptotic giant branch (AGB)
stars, or is it accreted externally through mergers? We examine the 2D stellar
and ionised gas kinematics of dusty ETGs using IFS observations from the SAMI
galaxy survey, and integrated star-formation rates, stellar masses, and dust
masses from the GAMA survey. Only 8% (4/49) of visually-classified ETGs are
kinematically consistent with being dispersion-supported systems. These
"dispersion-dominated galaxies" exhibit discrepancies between stellar and
ionised gas kinematics, either offsets in the kinematic position angle or large
differences in the rotational velocity, and are outliers in star-formation rate
at a fixed dust mass compared to normal star-forming galaxies. These properties
are suggestive of recent merger activity. The remaining 90% of dusty ETGs have
low velocity dispersions and/or large circular velocities, typical of
"rotation-dominated galaxies". These results, along with the general evidence
of published works on X-ray emission in ETGs, suggest that they are unlikely to
host hot, X-ray gas consistent with their low stellar mass when compared to
dispersion-dominated galaxies. This means dust will be long lived and thus
these galaxies do not require external scenarios for the origin of their dust
content.
