Upper limits on the presence of central massive black holes in two
  ultra-compact dwarf galaxies in Centaurus A
  The recent discovery of massive black holes (BHs) in the centers of high-mass
ultra compact dwarf galaxies (UCDs) suggests that at least some are the
stripped nuclear star clusters of dwarf galaxies. We present the first study
that investigates whether such massive BHs, and therefore stripped nuclei, also
exist in low-mass ($M<10^{7}M_{\odot}$) UCDs. We constrain the BH masses of two
UCDs located in Centaurus A (UCD320 and UCD330) using Jeans modeling of the
resolved stellar kinematics from adaptive optics VLT/SINFONI data. No massive
BHs are found in either UCD. We find a $3\,\sigma$ upper limit on the central
BH mass in UCD\,330 of $M_{\bullet}<1.0\times10^{5}M_{\odot}$, which
corresponds to 1.7\% of the total mass. This excludes a high mass fraction BH
and would only allow a low-mass BHs similar to those claimed to be detected in
Local Group GCs. For UCD320, poorer data quality results in a less constraining
$3\,\sigma$ upper limit of $M_{\bullet}<1\times10^{6}M_{\odot}$, which is equal
to 37.7\% of the total mass. The dynamical $M/L$ of UCD320 and UCD330 are not
inflated compared to predictions from stellar population models. The
non-detection of BHs in these low-mass UCDs is consistent with the idea that
elevated dynamical $M/L$s do indicate the presence of a substantial BH. Despite
not detecting massive BHs, these systems could still be stripped nuclei. The
strong rotation ($v/\sigma$ of 0.3 to 0.4) in both UCDs and the two-component
light profile in UCD330 support the idea that these UCDs may be stripped nuclei
of low-mass galaxies where the BH occupation fraction is not yet known.
