Intense C III] λλ1907,1909 emission from a strong Lyman continuum emitting galaxy

Abstract

We have obtained the first complete ultraviolet (UV) spectrum of a strong Lyman continuum (LyC) emitter at low redshift – the compact, low-metallicity, star-forming galaxy J1154+2443 – with a Lyman continuum escape fraction of 46% discovered recently. The Space Telescope Imaging Spectrograph spectrum shows strong Lyα and C III] λ1909 emission, as well as O III] λ1666. Our observations show that strong LyC emitters can have UV emission lines with a high equivalent width (e.g. EW(C III]) = 11.7 ± 2.9 Å rest-frame), although their equivalent widths should be reduced due to the loss of ionizing photons. The intrinsic ionizing photon production efficiency of J1154+2443 is high, log(ξ0ion = 25.56 erg−1 Hz), comparable to that of other recently discovered z ~ 0.3−0.4 LyC emitters. Combining our measurements and earlier determinations from the literature, we find a trend of increasing ξ0ion with increasing C III] λ1909 equivalent width, which can be understood by a combination of decreasing stellar population age and metallicity. Simple ionization and density-bounded photoionization models can explain the main observational features including the UV spectrum of J1154+2443.

Reconciling escape fractions and observed line emission in Lyman-continuum-leaking galaxies

“…(6)), we could also determine the corresponding value of the total LyC escape fraction for the χ 2 minimum. We also examined the weight of the ionizationbounded component ω in the DBC scenario (respectively (1 − ω) in the DBG scenario) to compare it to the UV covering fractions deduced from the Lyman series absorption lines (Gazagnes et al 2018;Chisholm et al 2018;Schaerer et al 2018). Hereafter, we summarize some interesting trends that merit further examination:…”

“…In the present work we study eleven z ∼ 0.3−0.4 Lyman continuum emitters discovered with the COS spectrograph on-board HST and whose properties have been amply discussed in several papers (Izotov et al 2016a(Izotov et al ,b, 2018aSchaerer et al 2016Schaerer et al , 2018Verhamme et al 2017;Gazagnes et al 2018;Chisholm et al 2018). The metallicities of these galaxies are in the range 12 + log(O/H) = 7.65−8.16, with a median oxygen abundance of 12 + log(O/H) of 7.91.…”

Intense C iv and He ii Emission in z ∼ 0 Galaxies: Probing High-energy Ionizing Photons∗

“…Relative to these works, the two galaxies presented here seem to have H-ionizing production efficiencies typical of low-mass, metal-poor, high-ionization z ∼ 0 galaxies (log ξ 0 ion ≥ 25.13, 25.18, depending on f esc ). However, the empirical relationship between ξ ion and total EW([O III]λλ4959 + 5007) from Chevallard et al (2018) Schaerer et al (2018) find a trend of increasing ξ ion with C III] λλ1907,1909 EW and note a large C III] EW for the local leaker, J1154+2443, which has a large LyC escape of f esc = 0.46. Extrapolating this C III] EW trend predicts log ξ ion > 25.8 for our galaxies (EW(C III]) = −16.4 and −18.4Å).…”

The Lyman Continuum Escape Survey. II. Ionizing Radiation as a Function of the [O iii]/[O ii] Line Ratio

“…Green triangles present individual (small) and composite (large) measurements of extreme emission line galaxies (EELGs) at z = 1.3 − 2.4 . Orange star illustrates a low-z strong LyC emitting galaxy, J1154+2334, with fesc = 0.46 (Izotov et al 2018a;Schaerer et al 2018 nificantly larger for LAEs than for continuum-selected LBGs. But again, we can see that both LyC-detected and non-detected LAEs subsamples have comparable values, log ξ ion ≃ 25.5 − 25.7, providing further evidence that the two populations of LAEs are spectroscopically indistinguishable.…”