25 July 2008

14 August 2008

Joseph Hennawi, University of Chicago, Berkeley

Quasars Probing Quasars: Understanding the Physics of Massive Galaxy Formation  

One of the most important problems in galaxy formation is understanding the physics which governs the observed bimodality in the galaxy population. Lower mass galaxies are gas rich and form a "blue cloud" in the color magnitude diagram, whereas more massive "red-and- dead" galaxies are gas poor and inhabit the red sequence. As a result, all galaxy formation models include some variant of feedback which acts to "quench" star formation in massive systems. Observing the formation epoch of red and dead galaxies will shed light on the physics behind this quenching. The strong clustering of luminous quasars at z ~ 2-3 indicates that they are indeed the progenitors of galaxies on the red sequence today. I will introduce a novel technique whereby a foreground quasar can be studied in absorption against a background quasar, resolving scales as small as 30kpc. This experiment reveals a rich absorption spectrum which contains a wealth of information about the physical conditions of gas in massive proto- galaxies. I will review absorption line modeling techniques and discuss the implications of these new observations for galaxy formation and feedback scenarios.

Tobias Goerdt, Racah Institute of Physics

Core creation in galaxies and haloes via sinking massive objects: application to binary nuclei  

Massive objects sinking within galaxies or dark matter haloes via dynamical friction will exchange momentum with central particles, ejecting them from the cusp and reducing the density of the inner region. We explore parameter space using numerical simulations and give empirical relations for the size of the resulting core within structures that have different initial cusp slopes. We show that simple energetic arguments can be used to predict these scaling laws. As an application we consider the dwarf spheroidal galaxy VCC 128 which has a double nucleus separated by less than a hundred parsecs. If this galaxy has a surrounding cold dark matter halo with central density proportional to r^-1 then these objects should sink to the centre of the cusp and coalesce in a few million years. We show that the sinking nuclei naturally create a core equal to their current separation if the initial dark matter cusp is slightly shallower than a log slope of -0.75 at around 0.1% of the virial radius. The sinking objects naturally stall at this radius for many Gyrs. This may be indirect observational evidence for central dark matter cusps shallower than r^-1 at the very centers of dark matter haloes.