On the dust properties of high-redshift molecular clouds and the connection to the 2175 Å extinction bump

Heintz, K. E.K. E.HeintzZafar, T.T.ZafarDe Cia, A.A.De CiaVergani, S. D.S. D.VerganiJakobsson, P.P.JakobssonFynbo, J. P. U.J. P. U.FynboWatson, D.D.WatsonJapelj, J.J.JapeljMøller, P.P.MøllerCOVINO, StefanoStefanoCOVINOKaper, L.L.KaperAndersen, A. C.A. C.Andersen2020-12-172020-12-1720190035-8711http://hdl.handle.net/20.500.12386/28954We present a study of the extinction and depletion-derived dust properties of gamma-ray burst (GRB) absorbers at 1 < z < 3 showing the presence of neutral atomic-carbon (C I). By modelling their parametric extinction laws, we discover a broad range of dust models characterizing the GRB C I absorption systems. In addition to the already well-established correlation between the amount of C I and visual extinction, AV, we also observe a correlation with the total-to-selective reddening, RV. All three quantities are also found to be connected to the presence and strength of the 2175 Å dust extinction feature. While the amount of C I is found to be correlated with the SED-derived dust properties, we do not find any evidence for a connection with the depletion-derived dust content as measured from [Zn/Fe] and N(Fe)dust. To reconcile this, we discuss a scenario where the observed extinction is dominated by the composition of dust particles confined in the molecular gas-phase of the interstellar medium (ISM). We argue that since the depletion level trace non-carbonaceous dust in the ISM, the observed extinction in GRB C I absorbers is primarily produced by carbon-rich dust in the molecular cloud and is therefore only observable in the extinction curves and not in the depletion patterns. This also indicates that the 2175 Å dust extinction feature is produced by dust and molecules in the cold and molecular gas-phase. This scenario provides a possible resolution to the discrepancy between the depletion- and SED-derived amounts of dust in high- z absorbers.STAMPAenOn the dust properties of high-redshift molecular clouds and the connection to the 2175 Å extinction bumpArticle10.1093/mnras/stz10122-s2.0-85067917405000474899400046https://academic.oup.com/mnras/article-abstract/486/2/2063/5437691?redirectedFrom=fulltext2019MNRAS.486.2063HFIS/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