The UV continuum of z > 1 star-forming galaxies in the Hubble ultraviolet Ultradeep Field

Peter Kurczynski, Eric Gawiser, Marc Rafelski, Harry I. Teplitz, Viviana Acquaviva, Thomas M. Brown, Dan Coe, Duilia F. De Mello, Steven L. Finkelstein, Norman A. Grogin, Anton M. Koekemoer, Kyoung Soo Lee, Claudia Scarlata, Brian D. Siana

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16 Scopus citations


We estimate the UV continuum slope, β, for 923 galaxies in the range 1 < z < 8 in the Hubble Ultradeep Field (HUDF). These data include 460 galaxies at 1 < z < 2 down to an absolute magnitude MUV = - 14(∼0.006Lz=1; 0.02 Lz=0), comparable to dwarf galaxies in the local universe. We combine deep HST/UVIS photometry in F225W, F275W, F336W wavebands (UVUDF) with recent data from HST/WFC3/IR (HUDF12). Galaxies in the range 1 < z < 2 are significantly bluer than local dwarf galaxies. We find their mean (median) values {β} = - 1.382(-1.830) ± 0.002 (random) ±0.1 (systematic). We find comparable scatter in β (standard deviation = 0.43) to local dwarf galaxies and 30% larger scatter than z > 2 galaxies. We study the trends of β with redshift and absolute magnitude for binned sub-samples and find a modest color-magnitude relation, dβ/dM = -0.11 ± 0.01, and no evolution in dβ/dM with redshift. A modest increase in dust reddening with redshift and luminosity, ΔE(B - V) ∼ 0.1, and a comparable increase in the dispersion of dust reddening at z < 2, appears likely to explain the observed trends. At z > 2, we find trends that are consistent with previous works; combining our data with the literature in the range 1 < z < 8, we find a color evolution with redshift, dβ/dz = -0.09 ± 0.01 for low luminosity (0.05 Lz=3), and dβ/dz = -0.06 ± 0.01 for medium luminosity (0.25 Lz=3) galaxies.

Original languageEnglish (US)
Article numberL5
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Sep 20 2014

Bibliographical note

Publisher Copyright:
© 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A.


  • Cosmology: observations
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift
  • Galaxies: structure


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