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Janet Bowey (Univ. Cardiff)

Carbonates and ices in the z = 0.89 galaxy-absorber towards PKS 1830–211 and within star-forming regions of the Milky Way
When Dec 06, 2022
from 10:35 AM to 11:55 AM
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The line of sight towards blazar PKS 1830–211 passes through a face-on lensing spiral galaxy at z=0.886. The absorber produces submm and radio absorption bands due to molecular species indicative of conditions similar to those of Milky-Way (MW) molecular clouds and HII regions associated with massive young stellar objects (YSOs). I decipher the carriers of solid-state infrared absorption features near 4.3, 4.6, 6.0 and 6.9 micron and compare the results with those for MW sightlines through the Taurus molecular cloud towards Elias 16, and massive YSOs in high-mass star forming regions (S140 IRS 1,

Mon R2 IRS 3, AFGL 989). I show that overlapping 6.9 micron components, due to carbonate dust and CH3OH ice, can be distinguished during feature fitting and that the derived
proportions are consistent with CH3OH:H2O ratios obtained from 3.0--4.0 micron spectra. Other dust components and associated features include H2O (6.0 micron) and CO2 (4.3 micron) ices and an organic residue OCN- (4.6 micron). The ratio of CH3OH ice to H2O ice in the PKS 1830--211 absorber (20--40 %) is 3--8 times the value in quescent MW molecular clouds and similar to the highest values obtained in massive MW YSOs; it is also consistent

with the unique detection of gas-phase submm CH3OH absorption in this galaxy-absorber. Carbonate mass-densities towards PKS 1830--211 and Elias 16 are similar to those detected in the circumstellar environment of the dust-forming post-AGB star Sakurai's Object. No
CH3OH was detected in Mon R2 IRS 3, but this source may contain 20-micron-sized SiC grains which contribute to an absorption plateau near 6.4 micron. Carbonate dust was not detected towards AFGL 989.