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

Journal
Date Issued
2019
Author(s)
Heintz, K. E.
•
Zafar, T.
•
De Cia, A.
•
Vergani, S. D.
•
Jakobsson, P.
•
Fynbo, J. P. U.
•
Watson, D.
•
Japelj, J.
•
Møller, P.
•
•
Kaper, L.
•
Andersen, A. C.
DOI
Abstract
We 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.
Volume
486
Issue
2
Start page
2063
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2019MNRAS.486.2063H
Rights
open.access
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