GRB‐selected galaxies through cosmic time

Abstract

To use the luminous gamma‐ray bursts and their afterglows as messengers from the early Universe has been advocated ever since the discovery of the cosmological nature of the GRB phenomenon in the late nineties. It took, however, until the advent of Swift to detect high‐redshift GRBs in significant numbers, and to provide the localization capabilities to enable statistical samples of GRBs free of selection biases and complete in redshift. I will present and discuss some of the recent progress in the field, with an emphasize on new results derived from sample studies and their implications for the nature of GRBs and their host galaxies. I will particularly focus on observations made with the seven‐channel imager GROND and X‐shooter, an optical/NIR echelle spectrograph mounted at the Very Large Telescope since 2009. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Galaxy gas as obscurer – II. Separating the galaxy-scale and nuclear obscurers of active galactic nuclei

“…We note that our results tend to produce high covering fractions, which are only consistent with the measurements because of large uncertainties. Despite our efforts to mitig-ate stellar mass and metallicity biases, we suppose that the use of LGRB host galaxies in Paper I, may affect our results when applied to AGN host galaxies: LGRB host galaxies are actively star forming (Levesque 2014;Krühler 2015;Perley et al 2016a) and thus may have slightly more gas than the average AGN galaxy. A correction in the column density by a factor of 2 would agree well with data points at all redshifts.…”

“…Black circles are the same, but only allow galaxies with sub-solar stellar metallicity as GRB hosts. Such a sub-selection is necessary to reproduce the mass and luminosity distribution of the observed GRB population (Hjorth & Bloom 2012;Vergani et al 2015;Krühler 2015;Perley et al 2016c). Curves present the median, while the errorbars represent the 1σ scatter in the population.…”

“…If we further consider that LGRBs only occur in galaxies with stellar metallicities below solar, we arrive at the results presented by black circles. Such a metallicity cut is necessary to reproduce the mass and luminosity distribution of the observed GRB population, as well as observed metal emission lines (Hjorth & Bloom 2012;Vergani et al 2015;Krühler 2015;Perley et al 2016c). Remarkably, the metallicity cut has little effect on the absorbing LOS metallicity.…”