Speaker:  Claudia Scarlata, SSC, Caltech

Abstract:  Extended Lyman alpha nebulae: hot or cold?

The mechanism powering Lyman alpha emission in extended Lyman alpha 
nebulae discovered at high redshifts is still elusive. These  nebulae 
are similar to those observed around high redshift radio galaxies, but 
they are not associated with either radio or Xray sources. Various 
mechanisms have been proposed to power the emission, including 
photoionization by a dust enshrouded AGN, interaction between the IGM 
and the super winds produced in a starburst, and cooling radiation from 
gas falling in a galaxy potential well. I will present recent results 
from a study of an extended Lyman-alpha nebula at z=2.4, associated with 
two dusty sources  at the same redshift.
Using a combination of rest-frame UV and mid-IR spectroscopy and imaging 
to constrain the source of energy, I find that the mechanism that best 
reproduces all the observed properties of this peculiar object is gas 
cooling through cold filaments.
I will also present some related results on the role that the dust 
geometry has on the escape of the Lyman alpha photons. Using a sample of 
z~0.3 Lyman alpha emitters I will show that Lyman alpha photons escape 
through clean line of sights within the galaxy, following similar paths 
traveled by Balmer and continuum photons