DISCOVERY OF z ∼ 8 GALAXIES IN THE HUBBLE ULTRA DEEP FIELD FROM ULTRA-DEEP WFC3/IR OBSERVATIONS

By R. Bouwens, G. Illingworth, P. Oesch, M. Stiavelli, P. V. van Dokkum, M. Trenti, D. Magee, I. Labbé, M. Franx, C. Carollo and 1 more. 2009

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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 ∼ 8–8.5, only 600 million years from recombination, using a Y105-dropout selection. The new 4.7 arcmin2 WFC3/IR observations reach to ∼28.8 AB mag (5σ) in the Y105J125H160 bands. These remarkable data reach ∼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 ∼ 8–8.5Y105-dropouts. We find five likely z ∼ 8–8.5 candidates. The sources have H160-band magnitudes of ∼28.3 AB mag and very blue UV-continuum slopes, with a median estimated β of ≲−2.5 (where fλ ∝ λβ). This suggests that z ∼ 8 galaxies are not only essentially dust free but also may have very young ages or low metallicities. The observed number of Y105-dropout candidates is smaller than the 20 ± 6 sources expected assuming no evolution from z ∼ 6, but is consistent with the five expected extrapolating the Bouwens et al. luminosity function (LF) results to z ∼ 8. These results provide evidence that the evolution in the LF seen from z ∼ 7 to z ∼ 3 continues to z ∼ 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∼ 8–9.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/be41b8aec1c03371c10219fcce09440187a33431

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In Astronomy and Astrophysics

  1. P. V. van Dokkum
  2. Richard S. Ellis
  3. M. Franx
  4. L. Hernquist
  5. P. Hopkins
  6. R. Bouwens
  7. Christopher J. Conselice
  8. R. Dav'e

In Instrumentation

  1. P. V. van Dokkum
  2. Richard S. Ellis
  3. M. Franx
  4. R. Bouwens
  5. Christopher J. Conselice
  6. G. Illingworth
  7. I. Labbé
  8. P. Oesch

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