Measuring 3D structure, dust extinction, and star formation histories from deep Hubble Space Telescope multi-color photometry in the Small Magellanic Cloud
Abstract
Dust properties in the Small Magellanic Cloud (SMC) provide insight into the interstellar environment of one of the closest analogs to early-Universe and low-metallicity galaxies. We examine the spatial variations in dust extinction curve properties and the three-dimensional structure in the Southwest Bar of the SMC using resolved stellar populations observed with the Hubble Space Telescope (HST) as a part of the Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE) program. Our eight-band HST photometry enables us to use color-magnitude diagrams (CMDs) of reddened red clump and red giant branch stars to simultaneously constrain SMC's 3D structure allowing us to accurately measure dust extinction from the CMD. Our CMD models are based on a detailed analysis of the SMC star formation history using red clump and red giant branch statistics to constrain the star formation rate and metallicity evolution of the SMIDGE region. We use the Bayesian Extinction And Stellar Tool (BEAST, Gordon et al. (2016)) to model the photometric effects of extinction on the spectral energy distribution of individual stars in SMIDGE taking into account a log-normal distribution of AV and an input extinction curve. We additionally model the relative positions of the stellar and dust distributions and the galactic depth along the line of sight. We then use CMD matching techniques similar to Dolphin (2002) based on Poisson statistics to extract the best-fit dust extinction and 3D structure parameters. We find a large line-of-sight depth (~ 10 kpc) and a slight offset of the dust on the near side of the stars resulting in a 0.65 - 0.70 reddened fraction. We find an extinction curve shape which varies only modestly even towards regions with high molecular gas content. These results yield the first detailed dust extinction curve properties in a key region in the SMC and have potential implications for how dust coagulates in molecular clouds in low-metallicity galaxies.
- Publication:
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American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23331106Y