PI: Sally Oey, University of Michigan, firstname.lastname@example.org
Address: Astronomy Department, 830 Dennison Building, Ann Arbor, MI 48109-1042, USA
CoI: Eric Pellegrini, University of Michigan
Title: The Optical Depth of \hii Regions of M33
Abstract: The fate of ionizing radiation from massive stars is of fundamental importance on scales ranging from individual stellar sources to cosmic reionization. We propose narrow-band emission-line imaging of the nearby spiral galaxy, M33, to directly observe the optical depths of its \hii region population, using the technique of ionization-parameter mapping. We will use the Mosaic-1.1 camera on the 4-m Mayall telescope, exploiting the newly upgraded detectors to obtain narrow-band imaging in \oii(lambda)3727. These data will be combined with existing Mosaic archive observations in \oiii(lambda)5007, \sii(lambda)6724, and \Ha, supplemented with new, deep observations and with new continuum imaging in the medium-width continuum filters BATC454 and BATC705. With these data, we will construct line ratio maps that will allow us to estimate the optical depth and escape fraction of ionizing radiation from all the observed \hii regions. We will quantitatively parameterize the Lyman continuum optical depth relative to the nebular and \hi properties, like the \Ha luminosity and \hi column density. Our results will yield a quantum advance in understanding the relationship between nebular optical depth and local ISM properties. This will thus clarify the role of density-bounded \hii regions in powering the diffuse, warm ionized medium (WIM). Our deep, narrowband dataset will provide a basis for future studies of the global WIM and ISM in this resolved, nearby galaxy; and the resulting spectacular emission-line imaging will be a wonderful resource for EPO purposes.
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