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Published September 10, 2016 | Submitted + Published
Journal Article Open

Spectroscopic Measurements of the Far-Ultraviolet Dust Attenuation Curve at z~3

Abstract

We present the first spectroscopic measurements of the shape of the far-ultraviolet (far-UV; λ = 950-1500 Å) dust attenuation curve at high redshift (z ~ 3). Our analysis employs rest-frame UV spectra of 933 galaxies at z ~ 3, 121 of which have very deep spectroscopic observations (≳7hr) at λ = 850 - 1300 Å, with the Low Resolution Imaging Spectrograph on the Keck Telescope. By using an iterative approach in which we calculate the ratios of composite spectra in different bins of continuum color excess, E(B-V), we derive a dust curve that implies a lower attenuation in the far-UV for a given E(B-V) than those obtained with standard attenuation curves. We demonstrate that the UV composite spectra of z ~ 3 galaxies can be modeled well by assuming our new attenuation curve, a high covering fraction of Hi, and absorption from the Lyman–Werner bands of H_2 with a small (≾20%) covering fraction. The low covering fraction of H_2 relative to that of the H_I and dust suggests that most of the dust in the ISM of typical galaxies at z ~ 3 is unrelated to the catalysis of H_2, and is associated with other phases of the ISM (i.e., the ionized and neutral gas). The far-UV dust curve implies a factor of ≈ 2 lower dust attenuation of Lyman continuum (ionizing) photons relative to those inferred from the most commonly assumed attenuation curves for L^* galaxies at z ~ 3. Our results may be utilized to assess the degree to which ionizing photons are attenuated in H ii regions or, more generally, in the ionized or low column density N(HI) ≾ 10^(17.2) cm^(−2) neutral ISM of high-redshift galaxies.

Additional Information

© 2016 American Astronomical Society. Received 2015 December 7; revised 2016 May 10; accepted 2016 May 23; published 2016 September 8. N.A.R. is supported by an Alfred P. Sloan Research Fellowship, and acknowledges the visitors program at the Institute of Astronomy in Cambridge, UK, where part of this research was conducted. C.C.S. acknowledges NSF grants AST-0908805 and AST-1313472. M.B. acknowledges support of the Serbian MESTD through grant ON176021. We thank Allison Strom for providing the photometry for the KBSS galaxies. We are grateful to the anonymous referee whose comments led to significant improvements in the presentation of the analysis. We wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, the observations presented herein would not have been possible.

Attached Files

Published - apj_828_2_107.pdf

Submitted - 1606.00434v1.pdf

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August 22, 2023
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