Friday, 20 February 2009

Explaining Lya Blobs as Cold Streams of Gas in the Halos of Galaxies

There have been several proposed mechanisms to power the extended diffuse Lyman-alpha emission (Lyman-alpha blobs, or LABs) that is sometimes associated with massive and active galaxies at high redshift.  One idea is that the we are observing cooling radiation from gas that is accreting onto the galaxies.  Dijkstra and Loeb endorse this idea, and specifically associate the radiation with cold accretion.

In their model, some fraction of the gravitational energy is converted into heat via weak shocks, which leads to the Ly-a emission.  By taking the cold gas fraction that comes from simulations, and putting in a few additional parameters, they are able to calculate the Ly-a emission as a function of halo mass.  This leads to the above figure.  The curves are different model predictions for how biased a region of space was probed by the survey that led to those data points (are there no good luminosity functions available for LABs?), so I think the comparison of the models and data is illustrative only.

No comments: