NARROWBAND IMAGING OF ESCAPING LYMAN-CONTINUUM EMISSION IN THE SSA22 FIELD
- Department of Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90024 (United States)
- California Institute of Technology, MS 105-24, Pasadena, CA 91125 (United States)
We present the results of an ultradeep, narrowband imaging survey for Lyman-continuum (LyC) emission at z {approx} 3 in the SSA22a field. We employ a custom narrowband filter centered at {lambda} = 3640 A (NB3640), which probes the LyC region for galaxies at z {>=} 3.06. We also analyze new and archival NB4980 imaging tuned to the wavelength of the Ly{alpha} emission line at z = 3.09, and archival broadband B, V, and R images of the non-ionizing UV continuum. Our NB3640 images contain 26 z {>=} 3.06 Lyman break galaxies (LBGs) as well as a set of 130 Ly{alpha} emitters (LAEs), identified by their excess NB4980 flux relative to the BV continuum. Six LBGs and 28 LAEs are detected in the NB3640 image. LBGs appear to span a range of NB3640-R colors, while LAEs appear bimodal in their NB3640-R properties. We estimate average UV-to-LyC flux density ratios, corrected for foreground contamination and intergalactic medium absorption, finding (F{sub UV}/F{sub LyC}){sup LBG}{sub corr} = 11.3{sup +10.3}{sub -5.4}, which implies an LBG LyC escape fraction f{sup LyC}{sub esc} {approx} 0.1, and (F{sub UV}/F{sub LyC}){sup LAE}{sub corr} = 2.2{sup +0.9}{sub -0.6}. The strikingly blue LAE flux density ratios defy interpretation in terms of standard stellar population models. Assuming (F{sub UV}/F{sub LyC}){sup LBG}{sub corr} applies down to L = 0.1L*, we estimate a galaxy contribution to the intergalactic hydrogen ionization rate that is consistent with independent estimates based on the Ly{alpha} forest opacity at z {approx_equal} 3. If we assume that (F{sub UV}/F{sub LyC}){sup LAE}{sub corr} holds at the faintest luminosities, the galaxy contribution significantly exceeds that inferred from the Ly{alpha} forest. We interpret our results in terms of a model where LyC photons escape over only {approx}10%-20% of solid angle. When advantageously oriented, a galaxy will exhibit a low UV-to-LyC ratio, an effect enhanced for more compact galaxies. This model, however, does not adequately explain the extremely blue NB3640-R colors measured for some LAEs in our sample. Further follow-up study of these faint LAEs is crucial, given the potentially important contribution similar objects make to the process of reionization.
- OSTI ID:
- 21578351
- Journal Information:
- Astrophysical Journal, Vol. 736, Issue 1; Other Information: DOI: 10.1088/0004-637X/736/1/18; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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