James, TA;
Viti, S;
Yusef-Zadeh, F;
Royster, M;
Wardle, M;
(2021)
Revealing the Physical Conditions around Sgr A* Using Bayesian Inference. I. Observations and Radiative Transfer.
Astrophysical Journal
, 916
(2)
, Article 69. 10.3847/1538-4357/abfd99.
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Abstract
We report subarcsecond Atacama Large Millimeter/submillimeter Array (ALMA) observations between 272 and 375 GHz toward Sgr A*'s circumnuclear disk (CND). Our data comprise eight individual pointings, with significant SiO (87–76) and SO (7–6) emission detected toward 98 positions within these pointings. Additionally, we identify H2CS (91,9–81,8), OCS (25–24), and CH3OH (21,1–20,2) toward a smaller subset of positions. By using the observed peak line flux density, together with a Bayesian inference technique informed by radiative transfer models, we systematically recover the physical gas conditions toward each of these positions. We estimate that the bulk of the surveyed gas has temperature Tkin < 500 K and density nH ⪅ 106 cm−3, consistent with previous studies of similar positions as traced by HCN clumps. However, we identify an uncharacteristically hot (Tkin ≈ 600 K) and dense (nH ≈ 106 cm−3) source in the Northeastern Arm. This position is found to be approximately consistent with a gravitationally bound region dominated by turbulence. We also identify a nearby cold (Tkin ≈ 60 K) and extremely dense (nH ≈ 107 cm−3) position that is again potentially bound and dominated by turbulence. We also determine that the total gas mass contained within the CND is MCND ≲ 4 × 104 M⊙. Furthermore, we qualitatively note that the observed chemical enrichment across large scales within the CND is consistent with bulk grain processing, though multiple desorption mechanisms are plausibly responsible. Further chemical modeling is required to identify the physical origin of the grain processing, as well as the localized H2CS and OCS emission.
| Type: | Article |
|---|---|
| Title: | Revealing the Physical Conditions around Sgr A* Using Bayesian Inference. I. Observations and Radiative Transfer |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.3847/1538-4357/abfd99 |
| Publisher version: | https://doi.org/10.3847/1538-4357/abfd99 |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | Interstellar medium; Molecular clouds; Star formation; Astrochemistry; Radiative transfer; Bayesian statistics; Observational astronomy; Spectral line identification |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10133440 |
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