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Towards Understanding the Galactic H II Region Sgr B1: Dust properties and Massive Stars

Presentation #343.03 in the session “Milky Way & Galactic Center”.

Published onJan 11, 2021
Towards Understanding the Galactic H II Region Sgr B1: Dust properties and Massive Stars

The central ~500 pc, known as the Central Molecular Zone (CMZ), contains the most dense molecular clouds in the Galaxy; however, the measured star formation rate (SFR) is an order of magnitude lower than expected, seriously challenging theoretical models of star formation(e.g. Barnes et al. 2017). Kruijssen et al. (2014) first posited a very compelling paradigm for star formation in the Galactic Center wherein episodic star formation is triggered as the dense molecular gas clouds orbiting the center pass by the central star cluster at Sgr A and the massive black hole Sgr A*. The result of this paradigm should be a string of H II regions and their ionizing stars that increase in age as a function of their distance from pericenter passage by Sgr A. The massive H II region, Sgr B1, however, does not fit into this model. Sgr B1 appears too dispersed to be as young as its orbital position - immediately adjacent to the very young star-forming region Sgr B2 - would suggest. We have obtained SOFIA observations of Sgr B1 using FORCAST and FIFI-LS to test this theory. We initially found (Simpson et al. 2018) that the stars ionizing Sgr B1 are NOT young and most likely did not form in situ, but instead are more evolved stars, possibly from an earlier generation of star formation. Additional FIFI-LS results on the line emission formed in photo-dissociation regions are presented at this meeting in the poster by Simpson et al.. Here we present the FORCAST observations, including new data obtained as part of one of the first SOFIA Legacy programs (Hankins et al. 2020), of Sgr B1 and examine the dust properties and geometry in the region. We present the dust temperature and opacity maps and explore the results in relation to with the known massive starsin the region. In addition, we have conducted observations with SpeX on IRTF in an effort to identify the additional ionization and heating sources required by our SOFIA observations, which have hitherto been unidentified. We have discovered two additional massive stars, and will present their spectral classifications and explore how they fit into the observations of the ionized gas and dust in Sgr B1.

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