Nadine Neumayer, C. Jakob Walcher
We present new upper limits for black hole masses in extremely late type
spiral galaxies. We confirm that this class of galaxies has black holes with
masses less than 10^6 Msolar, if any. We also derive new upper limits for
nuclear star cluster (NC) masses in massive galaxies with previously determined
black hole masses. We use the newly derived upper limits and a literature
compilation to study the low mass end of the global-to-nucleus relations. We
find the following (1) The M_BH-sigma relation cannot flatten at low masses,
but may steepen. (2) The M_BH-M_bulge relation may well flatten in contrast.
(3) The M_BH-Sersic n relation is able to account for the large scatter in
black hole masses in low-mass disk galaxies. Outliers in the M_BH-Sersic n
relation seem to be dwarf elliptical galaxies. When plotting M_BH versus M_NC
we find three different regimes: (a) nuclear cluster dominated nuclei, (b) a
transition region, and (c) black hole-dominated nuclei. This is consistent with
the picture, in which black holes form inside nuclear clusters with a very
low-mass fraction. They subsequently grow much faster than the nuclear cluster,
destroying it when the ratio M_BH/M_NC grows above 100. Nuclear star clusters
may thus be the precursors of massive black holes in galaxy nuclei.
View original:
http://arxiv.org/abs/1201.4950
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