- Broida 1640
Lucio Mayer, Institute for Theoretical Physics, University of Zurich
The emergence of bright Quasars as early as z >~ 7 strongly suggests the existence of a rapid pathway to form supermassive black holes. Conventional models based on the growth of light BH seeds from primordial Population III stars have difficulties in explaining such a rapid assembly. As a result, models in which massive BH seeds form by direct gas collapse in protogalaxies have received significant attention in the last few years. In the most common variants such models rely on fairly idealized thermodynamical conditions of gas flows in protogalaxies, such as suppression of cooling via dissociation of molecular hydrogen and metal-free gas in order to suppress fragmentation. We have recently developed a novel formation scenario that does not rely on any of such restrictive conditions (Mayer et al. 2010, Nature, 466, 1082). It is based on mergers between the most massive, already metal enriched protogalaxies at z <~ 10, in which gas inflows in excesse of 10^4 Mo/yr can arise in less than 10^5 yr following the merger. The latter gives rise to supermassive, gravitationally unstable nuclear clouds with masses in excesse of 10^8 Mo. These are likely precursors of massive BH seeds that could form after a short supermassive star and/or a quasi-star phase. I will show new simulations which confirm this scenario further using more sophisticated radiative cooling, highlighting the role of gravitoturbulence in achieving prominent inflows while minimizing the effect of fragmentation and star formation in the nuclear gas. Using the Millennium simulations combined with the latest semi-analytical galaxy formation models with black hole growth we compare our scenario with a Pop III-based scenario. We find specific signatures of massive BH seeds formed by our direct collapse in the clustering and morphology of the host galaxies at both high and low redshift. Our model is so far the only one consistent with very recent determinations of the accreting SMBH population in dropout galaxies at z~6-8.