Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies

• Published in: Monthly notices of the Royal Astronomical Society 2016-10, Vol.461 (4), p.3683-3701
• Main Authors: Izotov, Y. I., Schaerer, D., Thuan, T. X., Worseck, G., Guseva, N. G., Orlitová, I., Verhamme, A.
• Format: Article
• Language: English
• Subjects: Aluminum; Astronomy; Continuums; Disks; Emissions; Escape velocity; Galaxies; Hubble Space Telescope; Radiation; Red shift; Star & galaxy formation; Star formation; Symbols
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw1205

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] λ5007/[O ii] λ3727 ≳ 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) × 109 M⊙, high star formation rates, SFR ∼ 14–36 M⊙ yr−1, and high SFR densities, Σ ∼ 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] λ5007/[O ii] λ3727 ratios appears to pick up very efficiently sources with escaping LyC radiation: all five of our selected galaxies are LyC leakers.