Probing Small-Scale ISM Structure around Massive Stars in the Andromeda Galaxy (M31)
Massive stars are significant contributors of ionizing radiation and momentum, which can destroy surrounding gas in just a few Myrs. While most massive stars are observed in spiral structures associated with giant molecular clouds, we observe that massive stars also exist in the interarm regions of galaxies like M31, where relatively little star-forming material is observed at length scales greater than 10 pc.
By comparing the SED-fit line of sight extinction of massive stars (probing the sub-pc ISM structure) with other general ISM tracers (25-pc extinction maps, CO, HI), we find massive stars have on average the same amount of extinction at small scales, regardless of their location within a galaxy, indicating that even at 25-pc, we are still not capable of resolving star-forming ISM structures (Lindberg et al., 2024).
The entire catalog of 40,000 massive star candidates from the PHAT footprint can be downloaded from MAST.
Spatial distribution of massive star candidates (n=42,107) in M31 (Lindberg et al.~2024a), overlaid on a 24-$\mu$m Spitzer map. Sources are colored by their local (0.5-pc) extinction.
References
2024
Dust around Massive Stars Is Agnostic to Galactic Environment: New Insights from PHAT/BEAST
Christina Willecke Lindberg, Claire E. Murray, Julianne J. Dalcanton, and 2 more authors
Resolving the environments of massive stars is crucial for understanding their formation mechanisms and their impact on galaxy evolution. An important open question is whether massive stars found in diffuse regions outside spiral arms formed in situ or migrated there after forming in denser environments. To address this question, we use multiresolution measurements of extinction in the Andromeda galaxy (M31) to probe the interstellar medium surrounding massive stars across galactic environments. We construct a catalog of 42,107 main-sequence massive star candidates (M ≥ 8 M ⊙) using resolved stellar photometry from the Panchromatic Hubble Andromeda Treasury (PHAT) program, plus stellar and dust model fits from the Bayesian Extinction and Stellar Tool (BEAST). We quantify galactic environments by computing surrounding stellar densities of massive stars using kernel density estimation. We then compare high-resolution line-of-sight extinction estimates from the BEAST with 25 pc resolution dust maps from PHAT, measuring the total column density distribution of extinction. Our key finding is that, although the average total column density of dust increases with the density of massive stars, the average line-of-sight extinction toward massive stars remains constant across all environments. This suggests that massive stars have a uniform amount of dust in their immediate environment, regardless of their location in the galaxy. One possible explanation for these findings is that small molecular clouds are still capable of forming massive stars, even if they are not resolvable at 25 pc. These results indicate that massive stars are forming in the sparse regions of M31, as opposed to migrating there.
@article{lindberg2024,author={{Lindberg}, Christina Willecke and {Murray}, Claire E. and {Dalcanton}, Julianne J. and {Peek}, J.~E.~G. and {Gordon}, Karl D.},title={{Dust around Massive Stars Is Agnostic to Galactic Environment: New Insights from PHAT/BEAST}},journal={Astrophysical Journal},keywords={Massive stars, Interstellar medium, Hubble Space Telescope, Interstellar dust, Stellar populations, 732, 847, 761, 836, 1622, Astrophysics - Astrophysics of Galaxies},year={2024},month=mar,volume={963},number={1},eid={58},pages={58},doi={10.3847/1538-4357/ad18cc},archiveprefix={arXiv},eprint={2401.10991},primaryclass={astro-ph.GA},adsurl={https://ui.adsabs.harvard.edu/abs/2024ApJ...963...58L},adsnote={Provided by the SAO/NASA Astrophysics Data System}}
