Publication Date:
2016-07-24
Description:
Following our first detection reported in Izotov et al., we present the detection of Lyman continuum (LyC) radiation of four other compact star-forming galaxies observed with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope . These galaxies, at redshifts of z ~ 0.3, are characterized by high emission-line flux ratios [O iii ] 5007/[O ii ] 3727 5. The escape fractions of the LyC radiation f esc (LyC) in these galaxies are in the range of ~6–13 per cent, the highest values found so far in low-redshift star-forming galaxies. Narrow double-peaked Ly α emission lines are detected in the spectra of all four galaxies, compatible with predictions for LyC leakers. We find escape fractions of Ly α, f esc (Ly α) ~ 20–40 per cent, among the highest known for Ly α emitting galaxies. Surface brightness profiles produced from the COS acquisition images reveal bright star-forming regions in the centre and exponential discs in the outskirts with disc scalelengths α in the range ~0.6–1.4 kpc. Our galaxies are characterized by low metallicity, ~1/8–1/5 solar, low stellar mass ~(0.2–4) x 10 9 M , high star formation rates, SFR ~ 14–36 M yr –1 , and high SFR densities, ~ 2–35 M yr –1 kpc –2 . These properties are comparable to those of high-redshift star-forming galaxies. Finally, our observations, combined with our first detection reported in Izotov et al., reveal that a selection for compact star-forming galaxies showing high [O iii ] 5007/[O ii ] 3727 ratios appears to pick up very efficiently sources with escaping LyC radiation: all five of our selected galaxies are LyC leakers.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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