Le 5 décembre 2014
De 10h30 à 12h00
Jonathan Stern
Max-Planck-Institut für Astronomie, Heidelberg
Photo-ionization modelling of emission and absorption lines is widely used to derive metal abundances in quasars and star forming regions, constrain quasar and stellar spectra at unobservable ultraviolet wavelengths, and recently also to constrain the importance of radiation pressure feedback in models of star formation. In the commonly used constant-density models of photoionized gas, the gas density and the incident photon flux are independent free parameters. However, in a wide range of astrophysical environments, observations suggest that the distribution of gas densities scales with the photon flux, in contrast with the assumption that the two parameters are independent. Why does the gas density depend on the photon flux?
I will present the mechanism of radiation pressure confinement, in which the gas density distribution is set by pressure equilibrium of the gas with the incident radiation. I will compare the predictions of this mechanism with observations,
and discuss its implications for models of quasar feedback.