tokens: in the W 1 and W 2 bands and are characterized by W 1 − W 2 0.5 mag. Instead, the red W 1 − W 2 > 1 of our objects imply a considerable contribution of the warm and hot dust to their mid-infrared luminosity (Izotov et al. 2014a ). Three out of five galaxies were detected by WISE in the W 4 band at 22 μm. The estimated ratio of the 22 μm luminosity, which is a characteristic of warm dust, to the luminosity absorbed at 1500 Å in these galaxies is of order of unity (Table 9 ). As the luminosity of the cold dust emitting in the far-infrared range of extreme starbursts (not accessible to WISE ) is less or comparable to the luminosity of the warm dust (Izotov et al. 2014b ), we conclude that the UV luminosity absorbed in visible star-forming regions of our galaxies is consistent with the luminosity emitted by dust in the infrared range. Optical, near- and mid-infrared observations of other low-metallicity SFGs with similar properties suggest that they are relatively transparent (Izotov Thuan 2011 , 2016 ). That there is not much dust-obscured hidden star formation is also implied by the observed thermal free–free cm radio emission in dwarf galaxies with optical and infrared observations. Its flux density is consistent with the value derived from the flux density of the H β emission line (Izotov et al. 2014b ), indicating that there is not a considerable amount of additional star formation, not seen in the UV range, in our galaxies. 10 DISCUSSION To the best of our knowledge, our experiment is the first where compact SFGs with strong emission lines and high [O iii ]λ5007/[O ii ]λ3727 ratios are observed in the LyC. Furthermore, the entire sample (five out of five) at z ∼ 0.3 is found to emit LyC radiation, with absolute escape fractions ranging between 6 per cent and 13 per cent. Our observations thus significantly expand the sample of LyC leakers at low redshift, from four previously known galaxies (Leitet et al. 2013 ; Borthakur et al. 2014 ; Leitherer et al. 2016 ) to nine. The newly discovered sources also show significantly higher LyC escape fractions, compared to f esc (LyC) ≈ (1–4.5) per cent previously found. Apparently, the selection criteria we adopted are very efficient in finding LyC leakers. As such, this finding is probably one of the most important results of our study. Compactness and a peculiar emission line ratio as selection criteria, were previously already suggested to be related to LyC leakage. Jaskot Oey ( 2013 ) and Nakajima Ouchi ( 2014 ) have proposed that extreme [O iii ]λ5007/[O ii ]λ3727 ratios may be due to high escape fractions of ionizing photons and have argued that this could be the case for some ‘GP’ galaxies at z ∼ 0.1–0.3 or in z ∼ 2–3 LAEs. For comparison, Heckman et al. ( 2011 ) examined so-called Lyman-break analogues (LBAs) and suggested that a subset of them, those with a compact massive (∼10 9 M ⊙ ) dominant central object, could be LyC leakers. The LBAs have lower excitation and higher masses compared to
ner_tags: O O B-Wavelength I-Wavelength O B-Wavelength I-Wavelength I-Wavelength O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O B-Wavelength O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O B-Telescope O O B-Wavelength I-Wavelength I-Wavelength O B-Wavelength I-Wavelength O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O O O B-Telescope O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O B-Wavelength O B-Wavelength B-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O B-Wavelength O B-Wavelength O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O B-Wavelength O O O O O B-Wavelength O O O O O O O O O B-Formula I-Formula I-Formula O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O B-Wavelength O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O B-Citation I-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O B-Wavelength O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula O O B-Formula I-Formula I-Formula B-Wavelength O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O B-Wavelength O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O B-Wavelength O O O O O O O O