VERY BLUE UV-CONTINUUM SLOPE {beta} OF LOW LUMINOSITY z {approx} 7 GALAXIES FROM WFC3/IR: EVIDENCE FOR EXTREMELY LOW METALLICITIES?
- UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)
- Institute for Astronomy, ETH Zurich, 8092 Zurich (Switzerland)
- University of Colorado, Center for Astrophysics and Space Astronomy, 389-UCB, Boulder, CO 80309 (United States)
- Space Telescope Science Institute, Baltimore, MD 21218 (United States)
- Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands)
- Department of Astronomy, Yale University, New Haven, CT 06520 (United States)
- Carnegie Observatories, Pasadena, CA 91101 (United States)
We use the ultra-deep WFC3/IR data over the Hubble Ultra Deep Field and the Early Release Science WFC3/IR data over the CDF-South GOODS field to quantify the broadband spectral properties of candidate star-forming galaxies at z {approx} 7. We determine the UV-continuum slope {beta} in these galaxies, and compare the slopes with galaxies at later times to measure the evolution in {beta}. For luminous L* {sub z=3} galaxies, we measure a mean UV-continuum slope {beta} of -2.0 {+-} 0.2, which is comparable to the {beta} {approx} -2 derived at similar luminosities at z {approx} 5-6. However, for the lower luminosity 0.1L* {sub z=3} galaxies, we measure a mean {beta} of -3.0 {+-} 0.2. This is substantially bluer than is found for similar luminosity galaxies at z {approx} 4, just 800 Myr later, and even at z {approx} 5-6. In principle, the observed {beta} of -3.0 can be matched by a very young, dust-free stellar population, but when nebular emission is included the expected {beta} becomes {>=}-2.7. To produce these very blue {beta}s (i.e., {beta} {approx} -3), extremely low metallicities and mechanisms to reduce the red nebular emission seem to be required. For example, a large escape fraction (i.e., f {sub esc} {approx}> 0.3) could minimize the contribution from this red nebular emission. If this is correct and the escape fraction in faint z {approx} 7 galaxies is {approx}>0.3, it may help to explain how galaxies reionize the universe.
- OSTI ID:
- 21301411
- Journal Information:
- Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 708; ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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