Revealing the physical conditions around Sgr A using Bayesian inference. I. Observations and radiative transfer

Tomas A. James*, Serena Viti, Farhad Yusef-Zadeh, Marc Royster, Mark Wardle

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    2 Citations (Scopus)


    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.

    Original languageEnglish
    Article number69
    Pages (from-to)1-21
    Number of pages21
    JournalAstrophysical Journal
    Issue number2
    Publication statusPublished - 1 Aug 2021


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