On the lack of correlation between [O <scp>iii</scp>]/[O <scp>ii</scp>] and Lyman continuum escape fraction

Abstract

We present the first results of our pilot study of 8 photometrically selected\nLyman continuum (LyC) emitting galaxy candidates from the COSMOS field and\nfocus on their optical emission line ratios. Observations were performed in the\nH and K bands using the Multi-Object Spectrometer for Infra-Red Exploration\n(MOSFIRE) instrument at the Keck Observatory, targeting the [OII], H$\\beta$,\nand [OIII] emission lines. We find that photometrically selected LyC emitting\ngalaxy candidates have high ionization parameters, based on their high\n[OIII]/[OII] ratios (O32), with an average ratio for our sample of 2.5$\\pm$0.2.\nPreliminary results of our companion Low Resolution Imaging Spectrometer (LRIS)\nobservations, targeting LyC and Ly$\\alpha$, show that those galaxies with the\nlargest O32 are typically found to also be Ly$\\alpha$ emitters. High O32\ngalaxies are also found to have tentative non-zero LyC escape fractions\n($f_{esc}(LyC)$) based on $u$ band photometric detections. These results are\nconsistent with samples of highly ionized galaxies, including confirmed LyC\nemitting galaxies from the literature. We also perform a detailed comparison\nbetween the observed emission line ratios and simulated line ratios from\ndensity bounded H$_{\\textrm{II}}$ regions modeled using the photoionization\ncode MAPPINGS V. Estimates of $f_{esc}(LyC)$ for our sample fall in the range\nfrom 0.0-0.23 and suggest possible tension with published correlations between\nO32 and $f_{esc}(LyC)$, adding weight to dichotomy of arguments in the\nliterature. We highlight the possible effects of clumpy geometry and mergers\nthat may account for such tension.\n