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We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of nine low-mass star-forming galaxies at redshifts, z , in the range 0.3179–0.4524, with stellar masses |$M_\star \, \lt $| 108 M⊙ and very high specific star-formation rates sSFR ∼150–630 Gyr−1, aiming to study the dependence of leaking Lyman continuum (LyC) emission on stellar mass and some other characteristics of the galaxy. We detect LyC emission in four out of nine galaxies with escape fractions, f esc(LyC), in the range of 11–35 per cent, and establish upper limits for f esc(LyC) in the remaining five galaxies. We observe a narrow Ly α emission line with two peaks in seven galaxies and likely more complex Ly α profiles in the two remaining galaxies. The velocity separation between the peaks V sep varies in the range from ∼229 to ∼512 km s−1. Our additional data on low-mass galaxies confirm and strengthen the tight anticorrelation between f esc(LyC) and V sep found for previous low-redshift galaxy samples with higher stellar masses. V sep remains the best indirect indicator of LyC leakage. It is better than O32 on which f esc(LyC) depends weakly, with a large scatter. Finally, contrary to expectations, we find no increase of f esc(LyC) with decreasing galaxy stellar mass M ⋆. [ABSTRACT FROM AUTHOR]

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of eight compact star-forming galaxies at redshifts z = 0.02811–0.06540, with low oxygen abundances 12 + log(O/H) = 7.43–7.82 and extremely high emission-line flux ratios O32 = [O  iii ] λ5007/[O  ii ] λ3727 ∼ 22–39, aiming to study the properties of Ly α emission in such conditions. We find a diversity in Ly α properties. In five galaxies Ly α emission line is strong, with equivalent width (EW) in the range 45–190 Å. In the remaining galaxies, weak Ly α emission with EW(Ly α) ∼ 2–7 Å is superposed on a broad Ly α absorption line, indicating a high neutral hydrogen column density N (H  i) ∼ (1 – 3)× 1021 cm−2. We examine the relation between the Ly α escape fraction f esc(Ly α) and the Lyman continuum escape fraction f esc(LyC), using direct measures of the latter in eleven low-redshift LyC leakers, to verify whether f esc(Ly α) can be an indirect measure of escaping LyC radiation. The usefulness of O32, of the Ly α equivalent width EW(Ly α), and of the Ly α peak separation V sep as indirect indicators of Ly α leakage is also discussed. It is shown that there is no correlation between O32 and f esc(Ly α). We find an increase of f esc(Ly α) with increasing EW(Ly α) for EW(Ly α) <100 Å, but for higher EW(Ly |$\alpha)\gtrsim$| 150 Å the f esc(Ly α) is nearly constant attaining the value of ∼0.25. We find an anticorrelation between f esc(Ly α) and V sep, though not as tight as the one found earlier between f esc(LyC) and V sep. This finding makes V sep a promising indirect indicator of both the Ly α and ionizing radiation leakage. [ABSTRACT FROM AUTHOR]

We report the detection of the Lyman continuum (LyC) radiation of the compact star-forming 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 O32 = [O iii] λ5007/[O ii] λ3727 = 11.5. The escape fraction of the LyC radiation fesc(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 Ly α emission line is detected in the spectrum of J1154+2443 with a separation between the peaks Vsep of 199 km s−1, one of the lowest known for Ly α-emitting galaxies, implying a high fesc(Ly α). Comparing the extinction-corrected Ly α/H β flux ratio with the case B value, we find fesc(Ly α) = 98 per cent. Our observations, combined with previous detections in the literature, reveal an increase of O32 with increasing fesc(LyC). We also find a tight anticorrelation between fesc(LyC) and Vsep. 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+log O/H = 7.65 ± 0.01, the lowest stellar mass M⋆ = 108.20 M⊙, a similar star formation rate SFR = 18.9 M⊙ yr−1, and a high specific SFR of 1.2 × 10−7 yr−1. [ABSTRACT FROM AUTHOR]

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of nine low-mass star-forming galaxies at redshifts, z , in the range 0.3179–0.4524, with stellar masses |$M_\star \, \lt $| 108 M⊙ and very high specific star-formation rates sSFR ∼150–630 Gyr−1, aiming to study the dependence of leaking Lyman continuum (LyC) emission on stellar mass and some other characteristics of the galaxy. We detect LyC emission in four out of nine galaxies with escape fractions, f esc(LyC), in the range of 11–35 per cent, and establish upper limits for f esc(LyC) in the remaining five galaxies. We observe a narrow Ly α emission line with two peaks in seven galaxies and likely more complex Ly α profiles in the two remaining galaxies. The velocity separation between the peaks V sep varies in the range from ∼229 to ∼512 km s−1. Our additional data on low-mass galaxies confirm and strengthen the tight anticorrelation between f esc(LyC) and V sep found for previous low-redshift galaxy samples with higher stellar masses. V sep remains the best indirect indicator of LyC leakage. It is better than O32 on which f esc(LyC) depends weakly, with a large scatter. Finally, contrary to expectations, we find no increase of f esc(LyC) with decreasing galaxy stellar mass M ⋆. [ABSTRACT FROM AUTHOR]