http://arxiv.org/abs/1607.00288
Context: Several issues regarding the nature of dust at high redshift remain unresolved: its composition, its production and growth mechanisms, and its effect on background sources. Aims: This paper aims to provide a more accurate relation between dust depletion levels and dust-to-metals ratio (DTM), and to use the DTM to investigate the origin and evolution of dust in the high redshift Universe via GRB-DLAs. Methods: We use absorption-line measured metal column densities for a total of 19 GRB-DLAs, including five new GRB afterglow spectra from VLT/X-shooter. We use the latest linear models to calculate the dust depletion strength factor in each DLA. Using this we calculate total dust and metal column densities to determine a DTM. We explore the evolution of DTM with metallicity, and compare this to previous trends in DTM measured with different methods. Results: We find significant dust depletion in 16 of our 19 GRB-DLAs, yet 18 of the 19 have a DTM significantly lower than the Milky Way. We find that DTM is positively correlated with metallicity, which supports a dominant ISM-grain-growth mode of dust formation. We find a substantial discrepancy between the dust content measured from depletion and that derived from the total $V$-band extinction, $A_V$, measured by fitting the afterglow SED. We advise against using a measurement from one method to estimate that from the other, until the discrepancy can be resolved.
P. Wiseman, P. Schady, J. Bolmer, et. al.
Mon, 4 Jul 16
58/58
Comments: Submitted to Astronomy & Astrophysics. 12 pages, 8 figures
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