The UV Continuum of z > 1 Star-forming Galaxies in the Hubble Ultraviolet UltraDeep Field

September 2014 • 2014ApJ...793L...5K

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

Abstract • 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 M_UV= -14(∼ 0.006 L^*_z=1; 0.02 L^*_z=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 L^*_z=3), and dβ/dz = -0.06 ± 0.01 for medium luminosity (0.25 L^*_z=3) galaxies.

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Harry Teplitz

Senior Scientist