FLASH Talks: Modeling Ionized Gas in the Small Magellanic Cloud: The Wolf-Rayet Emission Nebula N76 & Is the Stellar Initial Mass Function Truly Universal?

Friday, 11 March 2022 noon — 1 p.m. MST

Elizabeth Tarantino (UMD) & Charles Steinhardt (Niehls Bohr Institute)
Elizabeth Tarantino, University of Maryland
Modeling Ionized Gas in the Small Magellanic Cloud: The Wolf-Rayet Emission Nebula N76
Massive stars inject energy and momentum into their surrounding gas, heating and influencing the physical conditions of the interstellar medium. The goal of this work is to understand the relationship between interstellar gas and star formation by determining the physical properties of the multiphase ISM. I will describe how we incorporate spatially resolved mid-infrared (MIR) and far-infrared (FIR) spectroscopy to model emission lines from the brightest Wolf-Rayet (WR) emission nebula N76 in the low metallicity Small Magellanic Cloud. We are particularly interested in determining the effects of metallicity on the ionized gas, as previous studies of unresolved low metallicity galaxies find hard radiation fields, extended bright [OIII] emission, and an overall more porous structure. We model the HII region N76 using the photoionization code Cloudy and find that modeling spatially resolved emission allows us to constrain properties much more accurately than using spatially integrated quantities. A spherical, constant density Cloudy model with a stellar wind-blown cavity reproduces the intensity and distribution of most ionized gas emission lines. I will then relate this work to accepted JWST programs and how they will improve our understanding of the cycle of gas, dust, and star formation in the nearby universe.
Charles Steinhardt, Niehls Bohr Institute
Is the Stellar Initial Mass Function Truly Universal?
Current techniques for analyzing large photometric catalogs are generally forced to assume a single, universal stellar initial mass function (IMF).  However, the IMF is predicted to depend upon the temperature of gas in star-forming molecular clouds, and thus should be expected to vary depending upon conditions within a star-forming galaxy.  The introduction of an additional parameter into photometric template fitting allows galaxies to be fit with a range of different IMFs.  Three surprising new features appear: (1) most star-forming galaxies are best fit with a bottom-lighter IMF than the Milky Way; (2) most star-forming galaxies at fixed redshift are fit with a very similar, but non-Milky Way IMF; and (3) the most massive star-forming galaxies at fixed redshift instead exhibit a less bottom-light IMF, which suggests quiescence may be the result of gas depletion rather than stochastic or environmental processes.  Finally, the lowest-mass star-forming galaxies appear to exhibit a distinct relationship between IMF and star formation rate, possibly hinting at distinct feedback mechanisms in the earliest stages of star formation.
FLASH Talks are scientific talks for the staff at NOIRLab and the University of Arizona's Steward Observatory. 
If you or a collaborator are interested in presenting at FLASH please get in touch. All FLASH talks are virtual for the foreseeable future, so feel free to suggest speakers from outside of Tucson!