Diffuse ionized gas and the Lyman continuum photon escape fraction in galaxies
IDPASC Portugal - PHD Programme 2015
2015 / 2016
Jean Michel Gomes
Universidade do Porto
Diffuse ionized gas (DIG) is an ubiquitous component in star-forming galaxies that permeates their disk and halo. The excitation mechanisms and ionization conditions of the DIG pose a long-standing problem. The prevailing picture though is that the DIG originates from Lyman continuum (LyC) photons escaping from sites of ongoing star formation and their reprocessing into nebular emission on scales of ~1 kpc away from HII regions. The mechanisms facilitating transport of LyC photons are unclear, it is yet likely that a key role is played by injection of energy and momentum by stellar winds and supernovae into the turbulent and porous multi-phase gas component of galaxies. Shocks, photoelectric heating, and a diffuse floor of gas ionization from hot evolved post-AGB stars could provide a further contribution to the formation of the DIG. Various lines of evidence indicate that 20-50% of the total Halpha emission in galaxies can be in diffuse DIG form, a fact that introduces an observational (surface brightness) bias with important consequences on estimates of star formation rates both in the local universe and in high-redshift galaxies. The goal of this PhD project is twofold: a) Using spatially resolved integral field spectroscopy (IFS) data from CALIFA (http://califa.caha.es) and other IFS galaxy surveys, in combination with higher-spatial resolution imaging data, to isolate the DIG and study its spatial and spectroscopic properties. A central question to be addressed on the basis of detailed studies of local Hubble-type galaxies is how the contribution of the DIG to the total Halpha luminosity (and, the LyC escape fraction from HII regions) is related to the recent star formation history of galaxies. b) The second goal of this project is to explore the LyC escape fraction in starburst galaxies using archival IFS data and single-fiber spectra from Sloan Digital Sky Survey.