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Lyman-alpha Escape From Green Peas with RASCAS

Presentation #144.01 in the session “Galaxy Evolution and Kinematics”.

Published onJan 11, 2021
Lyman-alpha Escape From Green Peas with RASCAS

Light emitted by massive stars from the first galaxies is hypothesized to have reionized the universe around redshift six. To test this hypothesis, we must understand how much ionizing (LyC) radiation was indeed able to escape from early galactic environments. The most promising observational probe to do this is the intense emission that young galaxies produce at the Lyman-alpha (LyA) wavelength. Indeed, the LyA escape fraction and emission peak separation are known to correlate with the LyC escape fraction in local star forming galaxies. Understanding the physical contexts surrounding these relationships is necessary for applying local relationships to the first galaxies when only the LyA signal is available. The interpretation of the LyA signal is challenging, however, reflecting the complex nature of the ISM and CGM both of which LyA radiation must successfully escape from in order to ionize intergalactic space. These environments typically show large column densities of neutral hydrogen and have a dynamical component by way of large scale galactic winds. Previous attempts to reproduce the LyA profiles in Green Pea galaxies -the only known local analogs of high redshift galaxies to consistently show LyC leakage - using models constrained by fitting steady spherical outflow models to UV spectral features have come up short. Recently, for the first time, we were able to constrain the bi-conical geometry of the outflows as well as their velocity field gradient in ten Green Pea galaxies using semi-analytical model fits to UV data. Using these constraints to better simulate the Green Peas in the radiation transfer software, RASCAS, we were able to predict the corresponding LyA profiles. We test both LyA radiation produced ex-situ or from recombination within the star forming regions, and LyA radiation produced in situ or from collisional excitations occurring in the outflows. We present our results in this poster


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