Hubble Space Telescope Wide Field Camera 3 Observations of Escaping Lyman Continuum Radiation from Galaxies and AGN at Redshifts z∼2.3-6.
Abstract
We present an assessment of how much of Lyman Continuum (LyC) radiation may be escaping from galaxies with measured spectroscopic redshifts at z∼2.29-5.98. For this, we analyzed the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) mosaics of the Early Release Science (ERS) field in four filters where LyC can be observed.With our best current assessment of the WFC3 systematics, we find that the LyC emission of faint galaxies at <z>∼2.37, 2.65, 3.45, and 5.23 is detected at the 1.7≥σ≥4.2 level in typical image stacks of 6-18 objects in the WFC3/UVIS filters F225W, F275W, F336W, and ACS/WFC F435W filter respectively. The LyC flux of weak AGN are detected at similar levels at z∼2.29-3.47, but with fewer objects in F225W and F275W.The measured signal corresponds to total LyC fluxes of mAB∼27.4-30.2 mag. With SED-fitting of the UV-continuum longwards of Lyα, the observed flux corresponds to an average LyC escape fraction of order fesc∼6-16% in these redshift bins, respectively. Our results suggest that faint galaxies collectively, and to some extent weak AGN, may have measurably contributed to maintaining cosmic reionization at redshifts z∼2.29-5.98, although their average LyC escape fractions are relatively low in this epoch. Complete reionization at z≤6-7 may additionally require the steep faint-end of the luminosity function of galaxies at higher redshifts, integration to very faint luminosities (MAB∼-14 to -10 mag), and possibly fesc increasing at those fainter luminosities and lower metallicities at higher redshifts than sampled here.
- Publication:
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American Astronomical Society Meeting Abstracts #225
- Pub Date:
- January 2015
- Bibcode:
- 2015AAS...22525516S