%0 Journal Article
%T Are Nuclear Star Clusters the Precursors of Massive Black Holes?
%A Nadine Neumayer
%A C. Jakob Walcher
%J Advances in Astronomy
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/709038
%X 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 106 , if any. We also derive new upper limits for nuclear star cluster 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 - relation cannot flatten at low masses, but may steepen. (2) The - relation may well flatten in contrast. (3) The -Sersic relation is able to account for the large scatter in black hole masses in low-mass disk galaxies. Outliers in the -Sersic relation seem to be dwarf elliptical galaxies. When plotting versus 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 / grows above 100. Nuclear star clusters may thus be the precursors of massive black holes in galaxy nuclei. 1. Introduction Supermassive black holes (BHs) are thought to be ubiquitous in the nuclei of massive galaxies. The discovery of a number of tight correlations between the global properties of galaxies and the properties of their nuclei (e.g., [1每3]) has led astronomers to realize that the evolution of galaxies may be closely linked to their nuclear properties. However, the nuclei of galaxies do not only host massive BHs but also host massive star clusters, commonly called nuclear star clusters (NCs). (Note that we here make the distinction between nucleus, that is, the location at the very center, and nuclear star cluster. Often the NC has been called nucleus or stellar nucleus in the past, but this seems ambiguous to us). The overall nucleation frequency is around 75% over all Hubble types ([4每6], hereafter B02), but NCs seem to be absent in the most massive galaxies [5, 7]. NCs typically have stellar velocity dispersions of 15每 , effective radii of a few parsecs, and dynamical masses of ~106每107 (B02 [8, 9]). Moreover, they show stellar populations of multiple ages [10每12], pointing towards them having a complex formation history. This might be related to their special location in the galaxy, as on average, NCs appear to sit at the photometric centre of their host galaxy [6, 13]. We recently showed that for bulgeless galaxies their location
%U http://www.hindawi.com/journals/aa/2012/709038/