J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons

Abstract

We report the detection of the Lyman continuum (LyC) radiation of the compact starforming galaxy (SFG) J1154+2443 observed with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope. This galaxy, at a redshift of z = 0.3690, is characterized by a high emission-line flux ratio O 32 = [O iii]λ5007/[O ii]λ3727 = 11.5. The escape fraction of the LyC radiation f esc (LyC) in this galaxy is 46 per cent, the highest value found so far in low-redshift SFGs and one of the highest values found in galaxies at any redshift. The narrow double-peaked Lyα emission line is detected in the spectrum of J1154+2443 with a separation between the peaks V sep of 199 km s −1 , one of the lowest known for Lyα-emitting galaxies, implying a high f esc (Lyα). Comparing the extinction-corrected Lyα/Hβ flux ratio with the case B value we find f esc (Lyα) = 98 per cent. Our observations, combined with previous detections in the literature, reveal an increase of O 32 with increasing f esc (LyC). We also find a tight anticorrelation between f esc (LyC) and V sep . The surface brightness profile derived from the COS acquisition image reveals a bright star-forming region in the centre and an exponential disc in the outskirts with a disc scale length α = 1.09 kpc. J1154+2443, compared to other known low-redshift LyC leakers, is characterized by the lowest metallicity, 12+logO/H = 7.65±0.01, the lowest stellar mass M = 10 8.20 M , a similar star formation rate SFR = 18.9 M yr −1 and a high specific SFR of 1.2×10 −7 yr −1 .

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

“…Our stacked LyC subsample with an average escape fraction f esc ∼ 0.35 has a large [O iii]/[O ii] line ratio of ≃ 10. Combining this measurement with individual LyC leaking sources at low-z(Izotov et al 2016a(Izotov et al ,b, 2018a as well as a single z = 3 LyC emitter, Ion2(Vanzella et al 2015;de Barros et al 2016), strengthens the positive correlation presented byIzotov et al (2018a) and…”

“…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.…”

The Lyman Alpha Reference Sample. X. Predicting Lyα Output from Star-forming Galaxies Using Multivariate Regression*

“…Given the success of our modelling at predicting global Lyα properties we can also attempt to predict more specific quantities, such as the velocity shift of the red peak. This size of velocity shift is related to the Lyα peak separation which has been claimed to be strongly correlated with the escape of Lyman continuum radiation (Izotov et al 2018) and also impacts the optical depth that the Lyα experiences as it travels through a neutral IGM. It would therefore be interesting if we could predict this quantity as well.…”

Outside the Lyman-break box: detecting Lyman continuum emitters at 3.5 < z < 5.1 with CLAUDS

“…Research by Izotov et al (2016Izotov et al ( , 2018b reports the detection of escaping LyC radiation from four compact star-forming galaxies (SFGs) 1 with f esc ∼ 6-13%. More recently, the same group reported the highest f esc = 46 ± 2% detection to date in low redshift compact SFGs (Izotov et al 2018a). These recent observational results indicate that all compact SFGs with reported LyC detections in Izotov et al (2016Izotov et al ( , 2018a share the same properties.…”

“…More recently, the same group reported the highest f esc = 46 ± 2% detection to date in low redshift compact SFGs (Izotov et al 2018a). These recent observational results indicate that all compact SFGs with reported LyC detections in Izotov et al (2016Izotov et al ( , 2018a share the same properties.…”