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Diffuse Lyα Emitting Halos: A Generic Property of High-redshift Star-forming Galaxies

Steidel, Charles C. and Bogosavljević, Milan and Shapley, Alice E. and Kollmeier, Juna A. and Reddy, Naveen A. and Erb, Dawn K. and Pettini, Max (2011) Diffuse Lyα Emitting Halos: A Generic Property of High-redshift Star-forming Galaxies. Astrophysical Journal, 736 (2). Art. No. 160. ISSN 0004-637X.

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Using a sample of 92 UV continuum-selected, spectroscopically identified galaxies with langzrang = 2.65, all of which have been imaged in the Lyα line with extremely deep narrow-band imaging, we examine galaxy Lyα emission profiles to very faint surface brightness limits. The galaxy sample is representative of spectroscopic samples of Lyman break galaxies (LBGs) at similar redshifts in terms of apparent magnitude, UV luminosity, inferred extinction, and star formation rate and was assembled without regard to Lyα emission properties. Approximately 45% (55%) of the galaxy spectra have Lyα appearing in net absorption (emission), with ≃20% satisfying commonly used criteria for the identification of "Lyα emitters" (LAEs; W 0(Lyα) ≥ 20 Å). We use extremely deep stacks of rest-UV continuum and continuum-subtracted Lyα images to show that all sub-samples exhibit diffuse Lyα emission to radii of at least 10" (~80 physical kpc). The characteristic exponential scale lengths for Lyα line emission exceed that of the λ_0 = 1220 Å UV continuum light by factors of ~5-10. The surface brightness profiles of Lyα emission are strongly suppressed relative to the UV continuum light in the inner few kpc, by amounts that are tightly correlated with the galaxies' observed spectral morphology; however, all galaxy sub-subsamples, including that of galaxies for which Lyα appears in net absorption in the spectra, exhibit qualitatively similar diffuse Lyα emission halos. Accounting for the extended Lyα emission halos, which generally would not be detected in the slit spectra of individual objects or with typical narrow-band Lyα imaging, increases the total Lyα flux (and rest equivalent width W _0(Lyα)) by an average factor of ~5, and by a much larger factor for the 80% of LBGs not classified as LAEs. We argue that most, if not all, of the observed Lyα emission in the diffuse halos originates in the galaxy H II regions but is scattered in our direction by H I gas in the galaxy's circum-galactic medium. The overall intensity of Lyα halos, but not the surface brightness distribution, is strongly correlated with the emission observed in the central ~1" —more luminous halos are observed for galaxies with stronger central Lyα emission. We show that whether or not a galaxy is classified as a giant "Lyα blob" (LAB) depends sensitively on the Lyα surface brightness threshold reached by an observation. Accounting for diffuse Lyα halos, all LBGs would be LABs if surveys were sensitive to 10 times lower Lyα surface brightness thresholds; similarly, essentially all LBGs would qualify as LAEs.

Item Type:Article
Related URLs:
URLURL TypeDescription
Steidel, Charles C.0000-0002-4834-7260
Shapley, Alice E.0000-0003-3509-4855
Kollmeier, Juna A.0000-0001-9852-1610
Reddy, Naveen A.0000-0001-9687-4973
Erb, Dawn K.0000-0001-9714-2758
Pettini, Max0000-0002-5139-4359
Additional Information:© 2011 The American Astronomical Society. Received 2011 January 10; accepted 2011 May 24; published 2011 July 19. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. This work has been supported by the US National Science Foundation through grants AST-0606912 and AST-0908805 (C.C.S.), and by the David and Lucile Packard Foundation (A.E.S.). C.C.S. acknowledges additional support from the John D. and Catherine T. MacArthur Foundation and the Peter and Patricia Gruber Foundation. D.K.E. was supported by the National Aeronautics and Space Administration under Award No.NAS7-03001 and the California Institute of Technology. Gwen Rudie and Olivera Rakic each provided very helpful comments on an earlier draft of the paper; we also thank Kurt Adelberger for his early involvement in the work which made the new results possible. We are grateful to the staff of the W. M. Keck Observatory who keep the instruments and telescopes running effectively. A careful reading and constructive report by the referee is very much appreciated. Finally, we wish to extend thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests.
Funding AgencyGrant Number
David and Lucile Packard FoundationUNSPECIFIED
John D. and Catherine T. MacArthur FoundationUNSPECIFIED
Peter and Patricia Gruber FoundationUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:cosmology: observations; galaxies: evolution; galaxies: high-redshift
Issue or Number:2
Classification Code:PACS: 98.80.Es; 98.62.Py; 98.54.Cm; 98.58.J.Hf
Record Number:CaltechAUTHORS:20110902-103429209
Persistent URL:
Official Citation:Diffuse Lyα Emitting Halos: A Generic Property of High-redshift Star-forming Galaxies Charles C. Steidel et al. 2011 ApJ 736 160
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:25209
Deposited By: Ruth Sustaita
Deposited On:02 Sep 2011 19:25
Last Modified:04 Dec 2019 23:03

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