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HST/ACS Lyman alpha imaging of the nearby starburst ESO338-IG04

M. Hayes·G. Ostlin·J. M. Mas-Hesse·D. Kunth·C. Leitherer·A. Petrosian
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Abstract

ESO338-IG04 is a well known, local, luminous Blue Compact Galaxy. It has a complex morphology and contains a central young starburst with compact young star clusters. The galaxy was imaged using HST/ACS in the Lyman alpha line and continuum. Using the Starburst99 synthetic spectra and other imaging data from HST/WFPC2 we developed a technique that allows us to make the first photometrically valid continuum subtraction for the LYa line. Our results are in qualitative agreement with the models of LYa escape being regulated by kinematical properties of the interstellar medium. The line-only image shows LYa in both emission and absorption. Notably, emission is seen from central bright young clusters and is in spatial agreement with the features present in a longslit spectrum taken with HST/STIS. Diffuse LYa emission regions are seen surrounding the central starburst where photons escape after one or more resonant scatterings in HI. These regions dominate the total LYa output. Photometry reveals a total LYa flux of 194 x 10^-14 erg/s/cm^2. Inside an artificial aperture matching that of the IUE satelite, we measure a LYa flux and equivalent width consistent with previous studies using the IUE. Analysis of parameter dependencies show our technique to be largely parameter independent, producing LYa maps indistinguishable from one another by eye and with fluxes consistent with one another to better than 50%. By comparison of LYa fluxes with Ha fluxes of a previous study, we estimate that each observed LYa photon has undergone ~2 additional scatterings. We see that LYa line closely correlate with other tracers of kinematics.

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M. Hayes, G. Ostlin, J. M. Mas-Hesse, D. Kunth, C. Leitherer, A. Petrosian. 2005-03-15. HST/ACS Lyman alpha imaging of the nearby starburst ESO338-IG04. https://doi.org/10.1051/0004-6361%3A20052702

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