On the lack of correlation between [O iii]/[O ii] and Lyman continuum escape fraction. Issue 4 (10th December 2018)

• Record Type: Journal Article
• Authors: Bassett, R; Ryan-Weber, E V; Cooke, J; Diaz, C G; Nanayakkara, T; Yuan, T-T; Spitler, L R; Meštrić, U; Garel, T; Sawicki, M; Gwyn, S; Golob, A
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 483:Issue 4(2019)
• Page Start: 5223
• Page End: 5245
• Publication Date: 2018-12-10
• Subjects: galaxies: intergalactic medium -- galaxies: ISM -- cosmology: dark ages, reionization, first stars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty3320
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present the first results of our pilot study of eight 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 [O ii ], H β, and [O iii ] emission lines. We find that photometrically selected LyC emitting galaxy candidates have high ionization parameters, based on their high [O iii ]/[O ii ] ratios (O32), with an average ratio for our sample of 2.5 ± 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 ii regions modelled using the photoionization code MAPPINGS V. Estimates of f esc (LyC) for our sample fall in the range from 0.0 to 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.