I am just branching out into areas that can be considered cosmology. Here is some very recent work in this area.

I work with Marta Volonteri, professor at University of Michigan and Francesco Haardt of Universitá dell'Insubria.

Volonteri, M., Haardt, F., & Gultekin, K. (2008), Compact Massive Objects in Virgo Galaxies: the Black Hole Population MNRAS accepted, arXiv:0710.5770.

We investigate the distribution of massive black holes (MBHs) in the Virgo cluster. Observations suggest that AGN activity is widespread in massive galaxies (M_* >= 10¹⁰ M_⊙), while at lower galaxy masses star clusters are more abundant, which might imply a limited presence of central black holes in these galaxy-mass regimes. We explore if this possible threshold in MBH hosting, is linked to nature, nurture, or a mixture of both. The nature scenario arises naturally in hierarchical cosmologies, as MBH formation mechanisms typically are efficient in biased systems, which would later evolve into massive galaxies. Nurture, in the guise of MBH ejections following MBH mergers, provides an additional mechanism that is more effective for low mass, satellite galaxies. The combination of inefficient formation, and lower retention of MBHs, leads to the natural explanation of the distribution of compact massive objects in Virgo galaxies. If MBHs arrive to the correlation with the host mass and velocity dispersion during merger-triggered accretion episodes, sustained tidal stripping of the host galaxies creates a population of MBHs which lie above the expected scaling between the holes and their hosts.

Occupation fraction of MBHs in Virgo galaxies. Dotted histogram: Decarli et al. 2007. Dashed histogram: no recoil. Dot- dashed histogram: â = 0. Solid histogram: â = 0.9. From bottom- left panel, clockwise: model I (higheff), model II (mideff), model III (peak3), model IV (peak3.5). The simulations give black hole occupation fraction (BHOF), which can be compared to the hatched histogram, which is the observed AGN fraction, a hard lower limit for observed BHOF.

MBH mass against baryonic mass of host galaxy. Circles: no recoil, Triangles: â = 0. Stars: â = 0.9. From bottom-left panel, clockwise: model I (higheff), model II (mideff), model III (peak3), model IV (peak3.5). The interesting points are the high outliers which come from galaxies that have had their baryonic mass reduced via tidal stripping with black hole mass left intact.