Carbonates and ices in the z = 0.89 galaxy-absorber towards PKS 1830?211 and within star-forming regions of the Milky Way

Bowey, Janet E. ORCID: https://orcid.org/0000-0003-3738-8857 2023. Carbonates and ices in the z = 0.89 galaxy-absorber towards PKS 1830?211 and within star-forming regions of the Milky Way. Monthly Notices of the Royal Astronomical Society 524 (2) , 2446–2459. 10.1093/mnras/stad1928

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Abstract

A pair of 6.0 and 6.9 μm absorption features are frequently observed in Milky Way (MW) molecular-clouds and YSOs; they also occur in the z = 0.886 rest-frame of a molecule-rich spiral galaxy obscuring blazar PKS 1830–211. I calibrate χ2-fitting methods, which match observations with two or three laboratory spectra. The 6.0-μm component is dominated by H2O ice, as expected. Included MW sources were selected using opacity criteria which limit the range of explored H2O-ice column densities to 1.6–2.4 × 1018 molecules cm−2, while the H2O-ice density in the galaxy absorber is (2.7 ± 0.5) × 1018 molecules cm−2. CH3OH ice and / or small (< 0.1-μm-sized) Ca- and Mg-bearing carbonates contribute at 6.9 μm. The 41 per cent CH3OH:H2O molecular ratio in the PKS 1830–211 absorber is significantly higher than in the molecular cloud towards Taurus-Elias 16 (<7.5 per cent) and similar to the highest value in MW YSOs (35 per cent in AFGL 989). Fitted carbonate (-CO3):H2O ratios in the galaxy absorber of 0.091 per cent are low in comparison to most of the ratios detected in the MW sample (0.2 per cent–0.4 per cent; ∼0 per cent in AFGL 989). Inorganic carbonates could explain the increased oxygen depletion at the diffuse-medium-to-molecular-cloud transition, which Jones and Ysard associated with unobserved organic carbonates or materials with a C:O ratio of 1:3.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Publisher:	Oxford University Press
ISSN:	0035-8711
Date of First Compliant Deposit:	23 November 2023
Date of Acceptance:	22 June 2023
Last Modified:	24 Nov 2023 09:45
URI:	https://orca.cardiff.ac.uk/id/eprint/164273

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