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arXiv · 1812.04129

On the Lack of Correlation Between [OIII]/[OII] and Lyman-Continuum Escape Fraction

R. Bassett·E. V. Ryan-Weber·J. Cooke·C. G. Diaz·T. Nanayakkara·T. -T. Yuan·L. R. Spitler·U. Meštrić·T. Garel·M. Sawicki·S. Gwyn·A. Golob
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Abstract

We present the first results of our pilot study of 8 photometrically selected Lyman continuum (LyC) emitting galaxy candidates from the COSMOS field and focus on their optical emission line ratios. Observations were performed in the H and K bands using the Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE) instrument at the Keck Observatory, targeting the [OII], H$β$, and [OIII] emission lines. We find that photometrically selected LyC emitting galaxy candidates have high ionization parameters, based on their high [OIII]/[OII] ratios (O32), with an average ratio for our sample of 2.5$\pm$0.2. Preliminary results of our companion Low Resolution Imaging Spectrometer (LRIS) observations, targeting LyC and Ly$α$, show that those galaxies with the largest O32 are typically found to also be Ly$α$ emitters. High O32 galaxies are also found to have tentative non-zero LyC escape fractions ($f_{esc}(LyC)$) based on $u$ band photometric detections. These results are consistent with samples of highly ionized galaxies, including confirmed LyC emitting galaxies from the literature. We also perform a detailed comparison between the observed emission line ratios and simulated line ratios from density bounded H$_{\textrm{II}}$ regions modeled using the photoionization code MAPPINGS V. Estimates of $f_{esc}(LyC)$ for our sample fall in the range from 0.0-0.23 and suggest possible tension with published correlations between O32 and $f_{esc}(LyC)$, adding weight to dichotomy of arguments in the literature. We highlight the possible effects of clumpy geometry and mergers that may account for such tension.

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R. Bassett, E. V. Ryan-Weber, J. Cooke, C. G. Diaz, T. Nanayakkara, T. -T. Yuan, L. R. Spitler, U. Meštrić, T. Garel, M. Sawicki, S. Gwyn, A. Golob. 2018-12-10. On the Lack of Correlation Between [OIII]/[OII] and Lyman-Continuum Escape Fraction. https://doi.org/10.1093/mnras%2Fsty3320

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