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