AMUSE-Field II. Nucleation of early-type galaxies in the field vs.
  cluster environment
  The optical light profiles of nearby early type galaxies are known to exhibit
a smooth transition from nuclear light deficits to nuclear light excesses with
decreasing galaxy mass, with as much as 80 per cent of the galaxies with
stellar masses below 10^10 Msun hosting a massive nuclear star cluster. At the
same time, while all massive galaxies are thought to harbor nuclear
super-massive black holes (SMBHs), observational evidence for SMBHs is slim at
the low end of the mass function. Here, we explore the environmental dependence
of the nucleation fraction by comparing two homogeneous samples of nearby field
vs. cluster early type galaxies with uniform Hubble Space Telescope (HST)
coverage. Existing Chandra X-ray Telescope data for both samples yield
complementary information on low-level accretion onto nuclear SMBHs.
Specifically, we report on dual-band (F475W & F850LP) Advanced Camera for
Surveys (ACS) imaging data for 28 out of the 103 field early type galaxies that
compose the AMUSE-Field Chandra survey, and compare our results against the
companion HST and Chandra surveys for a sample of 100 Virgo cluster early types
(ACS Virgo Cluster and AMUSE-Virgo surveys, respectively). We model the
two-dimensional light profiles of the field targets to identify and
characterize NSCs, and find a field nucleation fraction of 26% (+17%, -11%; at
the 1-sigma level), consistent with the measured Virgo nucleation fraction of
30% (+17%, -12%), across a comparable mass distribution. Coupled with the
Chandra result that SMBH activity is higher for the field, our findings
indicate that, since the last epoch of star formation, the funneling of gas to
the nuclear regions has been inhibited more effectively for Virgo galaxies,
arguably via ram pressure stripping.
