2009/10/31 by R. J. Bouwens, G. D. Illingworth, P. A. Oesch +9 · 6 citations
Engineering · Physics and Astronomy · #Astronomy and Astrophysical Research #CCD and CMOS Imaging Sensors #Galaxies: Formation, Evolution, Phenomena #Galaxy #Hubble Deep Field #Hubble Ultra-Deep Field #Luminosity #Luminous infrared galaxy #Measure (data warehouse) #Red shift #Spectral slope #astro-ph.CO
paper · pdf · doi:10.1088/2041-8205/708/2/l69
5 pages, 5 figures, accepted for publication in Astrophysical Journal Letters
openalex publication_date 2009/12/18 · arxiv created 2010/01/09 · arxiv updated 2015/05/14 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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 ∼ 7. We determine the UV-continuum slope β in these galaxies, and compare the slopes with galaxies at later times to measure the evolution in β. For luminous L * z =3 galaxies, we measure a mean UV-continuum slope β of −2.0 ± 0.2, which is comparable to the β ∼ −2 derived at similar luminosities at z ∼ 5–6. However, for the lower luminosity 0.1 L * z =3 galaxies, we measure a mean β of −3.0 ± 0.2. This is substantially bluer than is found for similar luminosity galaxies at z ∼ 4, just 800 Myr later, and even at z ∼ 5–6. In principle, the observed β of −3.0 can be matched by a very young, dust-free stellar population, but when nebular emission is included the expected β becomes ⩾−2.7. To produce these very blue βs (i.e., β ∼ −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 esc ≳ 0.3) could minimize the contribution from this red nebular emission. If this is correct and the escape fraction in faint z ∼ 7 galaxies is ≳0.3, it may help to explain how galaxies reionize the universe.