Lyman Continuum Emission Escaping from Green Pea Galaxies at z=0.5
Abstract
Metal-poor starburst galaxies may include many or most of the galaxies from which substantial Lyman continuum emission can escape. Li and Malkan (2018 ApJ 860, 83) used SDSS photometry to find a population of metal-poor starburst galaxies at z~0.5, from their strong [OIII]4959+5007 emission lines, which produce a detectable excess brightness in the i bandpass, compared with surrounding filters. We therefore used the HST/COS spectrograph to observe two of the newly discovered i-band excess galaxies around their Lyman limits. One has very strongly detected continuum below its Lyman limit, corresponding to an escape fraction of 18±3%. The other, which is less compact in UV imaging, has a 3-sigma upper limit to its Lyman escape fraction of < 5%. Before the UV spectroscopy, the existing data could not distinguish these two galaxies. This suggests that perhaps ~half of the strong [OIII] emitters as a class have significant ionizing photons escaping, and that might be determined by the luck of the particular viewing geometry. Obtaining the HST spectroscopy, revealed that the Lyman-continuum emitter differs in having no central absorption in its prominent Ly-alpha emission line profile. The other target, with no escaping Lyman continuum, shows the more typical double-peaked Ly-alpha emission. This profile signals the presence of a significant column of HI along our line-of-sight, which absorbs both Ly-alpha photons at the systemic redshift, and also Lyman limit photons which were emitted in our direction.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23516819M