Lyman-α spectral properties of five newly discovered Lyman continuum emitters

By A. Verhamme, I. Orlitová, Daniel Schaerer, Y. Izotov, G. Worseck, T. Thuan, N. Guseva. 2016

167 citations recorded by the source corpus.

Aims. We have recently reported the discovery of five low redshift Lyman continuum (LyC) emitters (LCEs) with absolute escape fractions f esc LyC that range from 6 to 13%, higher than previously found and that more than double the number of low redshift LCEs. We use these observations to test theoretical predictions about a link between the characteristics of the Lyman-alpha (Ly α ) line from galaxies and the escape of ionizing photons. Methods. We analyse the Ly α spectra of eight LCEs of the local Universe observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope (our five leakers and three galaxies from the litterature), and compare their strengths and shapes to the theoretical criteria and comparison samples of local galaxies: the Lyman Alpha Reference Survey, Lyman-break analogs, Green Peas, and the high-redshift strong LyC leaker Ion2 . Results. Our LCEs are found to be strong Ly α emitters, with high equivalent widths, EW (Ly α ) > 70 A, and large Ly α escape fractions, f esc Ly α > 20%. The Ly α profiles are all double-peaked with a small peak separation, in agreement with our theoretical expectations. They also have no underlying absorption at the Ly α position. All these characteristics are very different from the Ly α properties of typical star-forming galaxies of the local Universe. A subset of the comparison samples (2−3 Green Pea galaxies) share these extreme values, indicating that they could also be leaking. We also find a strong correlation between the star formation rate surface density and the escape fraction of ionizing photons, indicating that the compactness of star-forming regions plays a role in shaping low column density paths in the interstellar medium of LCEs. Conclusions. The Ly α properties of LCEs are peculiar: Ly α can be used as a reliable tracer of LyC escape from galaxies, complementing other indirect diagnostics proposed in the literature.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/88b5421f120450a48b26d768ea7c1d8cacb1c0ad

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In Astronomy and Astrophysics

1. Y. Izotov
2. T. Thuan
3. C. Conroy
4. P. Oesch
5. S. Tacchella
6. Usa
7. U. Virginia
8. Charlottesville

In Instrumentation

1. C. Conroy
2. T. Thuan
3. Y. Izotov
4. P. Oesch
5. S. Tacchella
6. S. Bose
7. R. Naidu
8. C. Mason

Citations in the corpus

• J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons (2017, background): “Following Verhamme et al. (2017) we also find a strong anticorrellation between the fesc and Vsep.”
• Low-redshift Lyman continuum leaking galaxies with high [O iii]/[O ii] ratios (2018, background): “Verhamme et al. (2017) have proposed that the presence of a double-peaked Lyα profile, with a small peak separation, would be a good indicator of LyC leakage.”
• Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, background): “For instance, the overwhelming majority of LyC leakers are compact (e.g., Izotov et al. 2018a) and show multi-peaked Lyα (e.g., Verhamme et al. 2017).”