Heintz, K. E.K. E.HeintzLedoux, C.C.LedouxFynbo, J. P. U.J. P. U.FynboJakobsson, P.P.JakobssonNoterdaeme, P.P.NoterdaemeKrogager, J. -K.J. -K.KrogagerBolmer, J.J.BolmerMøller, P.P.MøllerVergani, S. D.S. D.VerganiWatson, D.D.WatsonZafar, T.T.ZafarDe Cia, A.A.De CiaTanvir, N. R.N. R.TanvirMalesani, D. B.D. B.MalesaniJapelj, J.J.JapeljCOVINO, StefanoStefanoCOVINOKaper, L.L.Kaper2020-12-172020-12-1720190004-6361http://hdl.handle.net/20.500.12386/28908We present a survey for neutral atomic-carbon (C I) along gamma-ray burst (GRB) sightlines, which probes the shielded neutral gas-phase in the interstellar medium (ISM) of GRB host galaxies at high redshift. We compile a sample of 29 medium- to high-resolution GRB optical afterglow spectra spanning a redshift range through most of cosmic time from 1 < z < 6. We find that seven (≈25%) of the GRBs entering our statistical sample have C I detected in absorption. It is evident that there is a strong excess of cold gas in GRB hosts compared to absorbers in quasar sightlines. We investigate the dust properties of the GRB C I absorbers and find that the amount of neutral carbon is positively correlated with the visual extinction, A<SUB>V</SUB>, and the strength of the 2175 Å dust extinction feature, A<SUB>bump</SUB>. GRBs with C I detected in absorption are all observed above a certain threshold of logN(H I)/cm<SUP>-2</SUP> + [X/H] > 20.7 and a dust-phase iron column density of logN(Fe)<SUB>dust</SUB>/cm<SUP>-2</SUP> > 16.2. In contrast to the SED-derived dust properties, the strength of the C I absorption does not correlate with the depletion-derived dust properties. This indicates that the GRB C I absorbers trace dusty systems where the dust composition is dominated by carbon-rich dust grains. The observed higher metal and dust column densities of the GRB C I absorbers compared to H<SUB>2</SUB>- and C I-bearing quasar absorbers is mainly a consequence of how the two absorber populations are selected, but is also required in the presence of intense UV radiation fields in actively star-forming galaxies.STAMPAenArticle10.1051/0004-6361/2018342462-s2.0-85059480891000454400600004https://www.aanda.org/articles/aa/full_html/2019/01/aa34246-18/aa34246-18.html2019A&A...621A..20HFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation