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On the lack of correlation between [O III ]/[O II ] and Lyman continuum escape fraction

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posted on 2024-08-06, 11:55 authored by Robert Bassett, Emma Ryan-WeberEmma Ryan-Weber, Jeff CookeJeff Cooke, C. G. Diaz, Themiya NanayakkaraThemiya Nanayakkara, Tiantian Yuan, L. R. Spitler, U. Meštrić, T. Garel, M. Sawicki, S. Gwyn, A. Golob
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 [Oiii] 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.

Funding

ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions

Australian Research Council

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Detecting the deaths of the first stars: Investigating the physical processes in the early Universe

Australian Research Council

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ISSN

1365-2966

Journal title

Monthly Notices of the Royal Astronomical Society

Volume

483

Issue

4

Pagination

22 pp

Publisher

Oxford University Press

Copyright statement

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. Copyright © 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

Language

eng

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