LERMA Extra-Galactic group meeting: Abstracts

Wednesday 19th of September 2012:
Hoai Dothi "Gravitationally lensed extended sources: the case of QSO RXJ0911"

After a brief reminder of the mechanism of gravitational lensing of extended sources, the particular case of the host galaxy of QSO RXJ0911, a high redshift (z~2.8) quadruply imaged quasar, is explored. The non linearity of the problem, together with the proximity of the source to a cusp of the lens inner caustic, have important consequences on the dependence of the image appearance on the size and shape of the source. Their expected main features and their interpretation in terms of source extension and shape are investigated in a spirit of simplicity and in preparation for the analysis of high sensitivity and spatial resolution images that will soon be within reach with the completion of the Atacama Large Millimeter/submillimeter Array (ALMA). In particular, the information on source size carried by relative image brightness is discussed. Extension of the results to other types of quadruply imaged quasars is briefly considered.

Thursday 10th of November 2011:
Francesco Shankar "Empirically evolving super-massive Black Holes "

I will discuss semi-empirical models of the supermassive black hole and active galacticnucleus (AGN) populations, which incorporate the black hole growth implied by the observed luminosity function assuming a radiative efficiency ε and a distribution of Eddington ratios λ. By generalizing these continuity-equation models to allow a distribution P(λ|MBH, z) we are able to draw on constraints from observationally estimated λ distributions and active galaxy fractions while accounting for the luminosity thresholds of observational samples. I will proceed discussing the clustering of active galaxies up to very high redshifts, and conclude inserting black hole growth in the more general framework of galaxy evolution.

Thursday 27th of October 2011:
Greg Novak "Black Hole Fueling and AGN Feedback: Toward a deeper physical understanding"

We have performed axisymmetric hydrodynamic simulations black hole fueling and feedback in a massive galaxy. The effects of the central black hole on the temperature and momentum of galactic gas resulting from both radiative and mechanical feedback (in the form of a broad-line wind) are treated carefully using a detailed and physically well-motivated prescription. The simulations cover a range of length scales from ~1 pc to ~100 kpc. We carefully treat the forces on the gas due to dust opacity in the UV, optical, and IR bands from photons generated by both stars and the central AGN. We include a prescription for angular momentum transport, allowing us to consider galaxies with large specific angular momenta (disk galaxies) in the axisymmetric code. We consider the case of including steady cosmological infall of cold gas, as well as the case of the rapid removal of the angular momentum of a cold gas disk to mimic the effect of a galaxy merger. We find that the black hole accretion rate depends strongly on the inner radius of the simulation, implying that physical processes that operate on infalling gas between 1 and 100 pc have an important effect on the true black hole accretion rate and the resulting feedback processes.