Strong Lyman continuum emitting galaxies show intense CIV 1550 emission

Abstract

Using the Space Telescope Imaging Spectrograph, we have obtained ultraviolet (UV) spectra from ∼ 1200 to 2000 Å of known Lyman continuum (LyC) emitting galaxies at low redshift (z ∼ 0.3 − 0.4) with varying absolute LyC escape fractions ( f esc ∼ 0.01 − 0.72). Our observations include in particular the galaxy J1243+4646, which has the highest known LyC escape fraction at low redshift. While all galaxies are known Lyman alpha emitters, we consistently detect an inventory of additional emission lines, including C iv λ1550, He ii λ1640, O iii] λ1666, and C iii] λ1909, whose origin is presumably essentially nebular. C iv λ1550 emission is detected above 4 σ in six out of eight galaxies, with equivalent widths of EW(C iv) = 12 − 15 Å for two galaxies, which exceeds the previously reported maximum emission in low-z star-forming galaxies. We detect C iv λ1550 emission in all LyC emitters with escape fractions f esc > 0.1 and find a tentative increase in the flux ratio C iv λ1550/C iii] λ1909 with f esc . Based on the data, we propose a new criterion to select and classify strong leakers (galaxies with f esc > 0.1): C iv λ1550/C iii] λ1909 > ∼ 0.75. Finally, we also find He ii λ1640 emission in all the strong leakers with equivalent widths from 3 to 8 Å rest frame. These are among the highest values observed in star-forming galaxies and are primarily due to a high rate of ionizing photon production. The nebular He ii λ1640 emission of the strong LyC emitters does not require harder ionizing spectra at > 54 eV compared to those of typical star-forming galaxies at similarly low metallicity.

Scrutiny of a very young, metal-poor star-forming Lyα-emitter at z ~ 3.7

“…Following the results by Kakiichi & Gronke (2019), the estimated peak separation suggests a Lyman-continuum escape fraction 𝑓 LyC esc 15 per cent. This is also confirmed by the trend recently reported by Schaerer et al (2022) between the 𝑓 LyC esc and the C43 ratio (i.e. CIV𝜆1550/CIII𝜆1906, 1909.…”

“…CIV𝜆1550/CIII𝜆1906, 1909. According to their study, Schaerer et al (2022) report that galaxies with C43 < 0.75 typically have Lyman-continuum escape fraction below 10 per cent. For our target, the observed C43 ratio is equal to 0.18±0.03, thus reinforcing the conclusion that our target is a weak Lyman-continuum leaker.…”