DISCOVERY OF z {approx} 8 GALAXIES IN THE HUBBLE ULTRA DEEP FIELD FROM ULTRA-DEEP WFC3/IR OBSERVATIONS
- UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)
- Institute for Astronomy, ETH Zurich, 8092 Zurich (Switzerland)
- Space Telescope Science Institute, Baltimore, MD 21218 (United States)
- Department of Astronomy, Yale University, New Haven, CT 06520 (United States)
- University of Colorado, Center for Astrophysics and Space Astronomy, 389-UCB, Boulder, CO 80309 (United States)
- Carnegie Observatories, Pasadena, CA 91101 (United States)
- Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands)
We utilize the newly acquired, ultra-deep WFC3/IR observations over the Hubble Ultra Deep Field (HUDF) to search for star-forming galaxies at z {approx} 8-8.5, only 600 million years from recombination, using a Y {sub 105}-dropout selection. The new 4.7 arcmin{sup 2} WFC3/IR observations reach to {approx}28.8 AB mag (5{sigma}) in the Y {sub 105} J {sub 125} H {sub 160} bands. These remarkable data reach {approx}1.5 AB mag deeper than the previous data over the HUDF, and now are an excellent match to the HUDF optical ACS data. For our search criteria, we use a two-color Lyman break selection technique to identify z {approx} 8-8.5Y {sub 105}-dropouts. We find five likely z {approx} 8-8.5 candidates. The sources have H {sub 160}-band magnitudes of {approx}28.3 AB mag and very blue UV-continuum slopes, with a median estimated {beta} of {approx}<-2.5 (where f {sub {lambda}} {proportional_to} {lambda}{sup {beta}}). This suggests that z {approx} 8 galaxies are not only essentially dust free but also may have very young ages or low metallicities. The observed number of Y {sub 105}-dropout candidates is smaller than the 20 {+-} 6 sources expected assuming no evolution from z {approx} 6, but is consistent with the five expected extrapolating the Bouwens et al. luminosity function (LF) results to z {approx} 8. These results provide evidence that the evolution in the LF seen from z {approx} 7 to z {approx} 3 continues to z {approx} 8. The remarkable improvement in the sensitivity of WFC3/IR has enabled Hubble Space Telescope to cross a threshold, revealing star-forming galaxies at z{approx} 8-9.
- OSTI ID:
- 21301365
- Journal Information:
- Astrophysical Journal Letters, Vol. 709, Issue 2; Other Information: DOI: 10.1088/2041-8205/709/2/L133; Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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