The French-Italian XSHOOTER GTO program : investigating GRB host galaxies

Organisateur :

Date prévue : 15-19 Novembre 2010
Date définitive : 2010-11-15

Organisateur : Susanna Vergani (GEPI)

Gamma-ray bursts (GRBs) are the most powerful explosions since the formation of the Universe. They are associated with the gravitational collapse of stellar compact objects (neutron stars, black holes) or of massive stars exploding as supernovae. Thanks to their exceptional brightness, GRB afterglows can be used as powerful extragalactic background sources. They behave like distant lighthouses capable of unveiling the properties of the universe at different redshift. GRBs are traditionally divided in short (SGRBs, with duration less than 2 s and with harder spectra) and long (LGRBs, softer and of longer duration) subclasses. The typical nature of LGRB host galaxy is of a faint starforming galaxy, dominated by a young stellar population, with low masses.. Similar galaxies are hard to detect outside the local group, whereas GRB hosts can benefit from the very bright afterglow emission to accurately determine their position and redshift. In this context spectroscopy of high redshift GRBs represents a powerful tool to provide an invaluable piece of information to understand the galaxy evolution history in the Universe, since GRB hosts form a unique sample of typically faint and low mass galaxies which, unlike most other methods, is not selected on the luminosities of the galaxies themselves.

Our group belonging to the GEPI team co-lead, together with Italy, a French-Italian GTO program on the study of the chemical composition of long GRB host galaxies with the new ESO-VLT spectrograph XShooter. X-Shooter is the first ESO new second generation instrument and has the unique capability to produce intermediate resolution spectra from the UV to the near-infrared, covering simultaneously a spectral range from 3000 to 24000A. Thanks to the X-Shooter sensitivity and spectral range, we can determine the properties of the population of GRB host galaxies also at high redshift (nowadays most of the GRB host spectroscopical emission line studies are limited to z up to about 1.5) and will give very important information

on galaxy evolution, complementary to the one coming from the large surveys of high redshift galaxies. The observations have started in autumn 2009 and will continue for three years.

This atelier is the occasion to have a dedicated, face-to face meeting with our European collaborators to:

discuss the data analysis and interpretation (Xshooter is a new instrument with a new data reduction


prepare the first paper of the collaboration, presenting the results of the first year of the host galaxy


making the point on the IFU data, with an introduction on the scientific results that can be achieved

using this kind of observations and on the data reduction procedures;

fix the steps and objectives for future works.