Detections of [C II] 158 $\hat{I}¼$m and [O III] 88 $\hat{I}¼$m in a Local Lyman Continuum Emitter, Mrk 54, and its Implications to High-redshift ALMA Studies

Abstract

We present integral field, far-infrared (FIR) spectroscopy of Mrk 54, a local Lyman Continuum Emitter (LCE), obtained with FIFI-LS on the Stratospheric Observatory for Infrared Astronomy. This is only the second time, after Haro 11, that [C II] 158 $\hat{I}¼$m and [O III] 88 $\hat{I}¼$m spectroscopy of the known LCEs have been obtained. We find that Mrk 54 has a strong [C II] emission that accounts for $\sim 1$% of the total FIR luminosity, whereas it has only moderate [O III] emission, resulting in the low [O III]/[C II] luminosity ratio of $0.22\pm 0.06$. In order to investigate whether [O III]/[C II] is a useful tracer of $f_{\mathrm{esc}}$ (LyC escape fraction), we examine the correlations of [O III]/[C II] and (i) the optical line ratio of ${\mathrm{O}}_{32}\equiv$ [O III] 5007 Ã /[O II] 3727 Ã , (ii) specific star formation rate, (iii) [O III] 88 $\hat{I}¼$m/[O I] 63 $\hat{I}¼$m ratio, (iv) gas phase metallicity, and (v) dust temperature based on a combined sample of Mrk 54 and the literature data from the Herschel Dwarf Galaxy Survey and the LITTLE THINGS Survey. We find that galaxies with high [O III]/[C II] luminosity ratios could be the result of high ionization (traced by ${\mathrm{O}}_{32}$), bursty star formation, high ionized-to-neutral gas volume filling factors (traced by [O III] 88 $\hat{I}¼$m/[O I] 63 $\hat{I}¼$m), and low gas-phase metallicities, which is in agreement with theoretical predictions. We present an empirical relation between the [O III]/[C II] ratio and $f_{\mathrm{esc}}$ based on the combination of the [O III]/[C II] and ${\mathrm{O}}_{32}$ correlation, and the known relation between ${\mathrm{O}}_{32}$ and $f_{\mathrm{esc}}$. The relation implies that high-redshift galaxies with high [O III]/[C II] ratios revealed by ALMA may have $f_{\mathrm{esc}}\gtrsim 0.1$, significantly contributing to the cosmic reionization.

14 pages, 5 figures, Accepted for publication in ApJ