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Constraining Galactic Outflows and Lyman Alpha Escape in Star Forming Galaxies

Presentation #336.04D in the session Starburst Galaxies.

Published onJun 29, 2022
Constraining Galactic Outflows and Lyman Alpha Escape in Star Forming Galaxies

The neutral hydrogen Lyman Alpha (LyA) emission line is one of the brightest signals in the universe and offers great potential to constrain the neutral gas distribution of the circumgalactic medium (CGM) surrounding star forming galaxies. Reliable models capable of interpreting the LyA emission line therefore have the potential to constrain mass outflow rates and the escape fraction of Lyman continuum (LyC) radiation from the CGM — a key component for understanding the reionization history of the universe. So far, extracting the neutral gas distribution from the LyA signal has proven difficult, and there are no interpretive models capable of recovering the neutral gas distribution while simultaneously explaining other tracers of the neutral gas such as low-ionization state (LIS) metal lines. For my thesis work, I developed a semi-analytical line transfer (SALT) model to interpret the spectra of galactic outflows. By modeling both the resonant absorption and reemission of photons by an outflowing medium, SALT is able to constrain the gas properties of the entire CGM — a vast improvement from prior models which typically consider only line of sight absorption. I used SALT to check for relationships between properties of LIS gas with LyA escape and found that the geometry of the LIS gas is the primary factor influencing LyA escape. My results also suggest that for spherical outflows the escape of LyA radiation and the LyA luminosity both increase with the extent of the galactic winds, suggesting that a significant portion of the LyA signal may be coming from the wind itself, rather than just from recombination events in HII regions. Using the SALT model constraints, I am now in the process of modeling the LyA radiative transfer in Green Pea galaxies to predict the observed LyA profiles. If successful, then the reverse process will become possible — that is, to predict the neutral gas distribution form the LyA signal.

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