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

## TL;DR

This study investigates the relationship between optical emission line ratios and Lyman-Continuum escape fractions in galaxies, finding no strong correlation and highlighting the complexity of factors influencing LyC escape.

## Contribution

First observational analysis linking [OIII]/[OII] ratios with LyC escape fractions, challenging existing correlations and suggesting additional influencing factors.

## Key findings

- High [OIII]/[OII] ratios correlate with Lyα emission.
- Estimated LyC escape fractions range from 0.0 to 0.23.
- Tension with previous correlations between O32 and LyC escape fraction.

## 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$\beta$, 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$0.2. Preliminary results of our companion Low Resolution Imaging Spectrometer (LRIS) observations, targeting LyC and Ly$\alpha$, show that those galaxies with the largest O32 are typically found to also be Ly$\alpha$ 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.