Abstract
| Vergani |
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| Probing the metallicity of the neutral gas in galaxies up to the end of the reionization |
| GRBs have been heralded as effective probes to study the chemical evolution of star-forming galaxies up to the highest redshift. They are associated with massive stars and their bright afterglows can be used as powerful background sources capable of unveiling the gas along their line-of-sight, including that of their host galaxies. An opportunity to explore the metal abundances of the neutral gas of a L* galaxy at the end of the reionisation epoch was provided by the bright GRB 210905A at redshift z = 6.3. In this talk I will present the spectroscopic observation of its afterglow as well as the photometric observation of its host galaxy. ESO VLT/X-shooter optical spectroscopy allowed to detect and characterize in detail neutral-hydrogen, low-ionization, high-ionization and fine-structure absorption lines, as well as a tentative Lyman-α emission at velocity > 1000 km s^-1 from the absorbing gas. Metallicity, kinematics, chemical abundance pattern, dust depletion and dust-to-metal mass ratio could be determined for the neutral gas of GRB host galaxy. Additionally, late-time HST observations of the GRB field hint for a complex GRB host galaxy system. I will place these results in a more general study on the evolution of the dust and metal content of galaxies as probed by GRBs, compared with that predicted by galaxy simulations. These results show the power of GRB absorption line spectroscopy as a direct way to probe the metal enrichment of the neutral gas of galaxies also at high redshift, otherwise of extremely difficult access, even in the JWST era. |