Diverse properties of Ly α emission in low-redshift compact star-forming galaxies with extremely high [O iii]/[O ii] ratios. Issue 1 (31st October 2019)

• Record Type: Journal Article
• Authors: Izotov, Y I; Schaerer, D; Worseck, G; Verhamme, A; Guseva, N G; Thuan, T X; Orlitová, I; Fricke, K J
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 491:Issue 1(2020)
• Page Start: 468
• Page End: 482
• Publication Date: 2019-10-31
• Subjects: galaxies: abundances -- galaxies: dwarf -- galaxies: fundamental parameters -- galaxies: ISM -- galaxies: starburst -- dark ages, reionization, first stars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz3041
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: 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)× 10 21 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.