Galaxy formation and evolution

Abstract:

The GalICS (Galaxies in Cosmological Simulations) semi-analytical model of hierar- chical galaxy formation is used to investigate the effects of different galactic properties, including star formation rate (SFR) and outflows, on the shape of the mass metallic- ity relation and to predict the relation for galaxies at redshift z=2.27 and z=3.54. Our version of GalICS has the chemical evolution implemented in great detail and is less heavily reliant on approximations such as instantaneous recycling. We vary the model parameters controlling both the efficiency and redshift dependence of the SFR as well as the efficiency of supernova feedback. We find that the factors controlling the SFR influence the relation significantly at all redshifts and require a strong redshift dependence, proportional to 1+z, in order to reproduce the observed relation at the low mass end. Indeed, at any redshift, the predicted relation flattens out at the high mass end resulting in a poorer agreement with observations in this regime. We also find that variation of the parameters associated with outflows has a minimal effect on the relation at high redshift but does serve to alter its shape in the more recent past. We thus conclude that the relation is one between SFR and mass and that outflows are only important in shaping the relation at late times. When the relation is stratified by SFR it is apparent that the predicted galaxies with increasing stellar masses have higher SFRs, supporting the view that galaxy downsizing is the origin of the relation. Attempting to reproduce the observed relation, we vary the parameters controlling the efficiency of star formation and its redshift dependence and compare the predicted relations with Erb et al. (2006) at z=2.27 and Maiolino et al. (2008) at z=3.54 in order to find the best-fitting parameters. (Abridged)

Abstract:

We construct mass models of 28 S0-Sb galaxies. The models have an axisymmetric stellar component and a NFW dark halo and are constrained by observed KS-band photometry and stellar kinematics. The median dark halo virial mass is 1012.8 M⊙, and the median dark/total mass fraction is 20% within a sphere of radius r1/2, the intrinsic half-light radius, and 50% within R25. We compare the Tully-Fisher relations of the spirals and S0s in the sample and find that S0s are 0.5 mag fainter than spirals at KS-band and 0.2 dex less massive for a given rotational velocity. We use this result to rule out scenarios in which spirals are transformed into S0s by processes which truncate star formation without affecting galaxy dynamics or structure, and raise the possibility of a break in homology between spirals and S0s. © 2010 American Institute of Physics.

Abstract:

We show that high quality laser guide star (LGS) adaptive optics (AO) observations of nearby early-type galaxies are possible when the tip-tilt correction is done by guiding on nuclei while the focus compensation due to the changing distance to the sodium layer is made 'open loop'. We achieve corrections such that 40% of flux comes from R<0.2 arcsec. To measure a black hole mass (M•) one needs integral field observations of both high spatial resolution and large field of view. With these data it is possible to determine the lower limit to M• even if the spatial resolution of the observations are up to a few times larger than the sphere of influence of the black hole. © 2010 American Institute of Physics.

Abstract:

We summarize the recent results of our survey of the nearest nuclear star clusters. The purpose of the survey is to understand nuclear star cluster formation mechanisms and constrain the presence of black holes using adaptive optics assisted integral field spectroscopy, optical spectroscopy, and HST imaging in 13 galaxies within 5 Mpc. We discuss the formation history of the nuclear star cluster and possible detection of an intermediate mass BH in NGC 404, the nearest S0 galaxy. © 2010 American Institute of Physics.