STScI Spring Symposium 2024: Dust around Massive Stars Is Agnostic to Galactic Environment: New Insights from PHAT/BEAST

Transcript

1. Intro ✦ One main processes in a galactic ecosystem is the exchange of energy and momentum between stars and the interstellar medium (ISM), i.e. gas cools to form stars; stars heat up the ISM, halting further star formation. ✦ The majority of energy in heating the ISM stems from massive stars (Minit > 8 M ), so, it is vital that we understand where massive stars form and exist in galaxies. Method ✦ Emission from massive stars is expected to peak in the NUV, however, this brightness can be greatly extinguished by any dust lying along the line-of-sight (since dust preferentially extinguishes shorter wavelengths). ✦ We use the Bayesian Extinction and Stellar Tool (BEAST; Gordon+16) to characterize the stellar types and line-of-sight dust (~0.5-pc) of over 42k massive star candidates in M31 using photometry from the PHAT (Dalcanton+12). ⊙ By constructing a catalog of over 42,000 massive stars in M31, we find most massive stars in sparse regions likely formed in-situ, as opposed to migrating there. DUST AROUND MASSIVE STARS IS AGNOSTIC TO GALACTIC ENVIRONMENT: NEW INSIGHTS FROM PHAT/BEAST Christina W. Lindberg1 (clindbe2@jhu.edu), Claire Murray2, Julianne Dalcanton3, Josh Peek2, Karl Gordon2 1. Johns Hopkins University; 2. Space Telescope Science Institute; 3. Flatiron Institute BEAST; Gordon+16 λ VISIBLE Flux NIR NUV STELLAR MODEL [initial mass, age, metallicity] DUST MODEL [extinction (AV), grain size (RV), extinction curve] Results ✦ We use Kernel Density Estimation (k=100 pc) to quantify the density of massive stars across the disk. ✦ We measure the median amount of dust content at the location of each massive star using dust maps at 25-pc resolution from Dalcanton+15. This Av scales logarithmically with the stellar densities. ✦ However, at ~0.5-pc resolution, line-of-sight Av is not correlated with galactic environment and remains constant across all stellar densities. Discussion ✦ If the massive stars in the inter-arm regions had migrated from the denser rings, we would expect their line-of-sight extinction to sample from the total dust content in the region, and should therefore follow a similar trend as the extinction at 25-pc resolution. ✦ Discrepancy between the two measurements indicates that massive stars in sparse environments are not runaway stars, but likely formed in situ from ISM structures unresolved at 25-pc. Background: Spitzer 24-micron emission Minit ≥ 8M⊙