Friday, 24 July 2009

D'Onghia, Springel, Hernquist & Keres, "Substructure depletion in the milky way halo by a disk". The put a disk in a cosmologically simulated halo, by hand and observe a lot of stripping of the mass of subhaloes by disk shocking. This reduces the amount of substructure in the inner halo and may help solving the missing satellite problem...

Friday, 10 July 2009

Narrow-line AGN and their host galaxies

from Greene et al., arXiv:0907.1086

In this paper several aspects of 0.1<z<0.4 narrow-line (obscured) AGN
and their host galaxies are investigated. The sample was selected
from the SDSS and higher-quality follow-up spectra were taken with
Magellan; derived properties include AGN line widths, stellar velocity
dispersions, and Eddington ratios.

The plot above is particularly notable, showing the [OIII] width (i.e.
gas velocity dispersion) compared to the stellar velocity dispersion.
There's no apparent correlation, indicating that gas in the galaxy is
very much out of equilibrium with the stars; from this the authors
conclude that the AGN must be affecting the gas properties on a
galaxy-wide scale.

The diversity of type 1a supernovae from broken symmetries

Stellar mass growth over cosmic time

Several authors have found that the SFR of star-forming galaxies is approximately proportional to stellar mass to the first power, and that the constant of proportionality decreases with redshift. Using such a relation, it is straightforward to parameterize the growth of a galaxy
(ignoring major mergers) given it's observed redshift and stellar mass.

This letter by Alvio Renzini, discusses this issue. Renzini takes a recent parameterization of the SFR from the literature, and estimates how a galaxy at z=3 (when the universe was 2Gyr old) will grow. The upper red curve in the plot above shows the growth of stellar mass for the published parameterization... but obviously a typical observed galaxy can't grow in mass by 5 orders of magnitude from z=3 to z=0. So the lower red curves show how the growth will occur if you reduce the SFR at all redshifts by a factor of \eta.

The letter goes on to briefly discuss how environment, mergers, and morphological transformations/quenching will affect galaxy growth.