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Extended and filamentary Lyα emission from the formation of a protogalactic halo at z = 2.63

Rauch, Michael and Becker, George D. and Haehnelt, Martin G. and Gauthier, Jean-Rene and Sargent, Wallace L. W. (2013) Extended and filamentary Lyα emission from the formation of a protogalactic halo at z = 2.63. Monthly Notices of the Royal Astronomical Society, 429 (1). pp. 429-443. ISSN 0035-8711. doi:10.1093/mnras/sts346.

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We report the observation of a further asymmetric, extended Lyα emitting halo at z = 2.63, from our ultra-deep, long-slit spectroscopic survey of faint high-redshift emitters, undertaken with Magellan LDSS3 in the GOODS-S field. The Lyα emission, detected over more than 30 kpc, is spatially coincident with a statistically significant concentration of galaxies visible in deep broad-band imaging. While these faint galaxies without spectroscopic redshifts cannot all with certainty be associated with one another or with the Lyα emission, there are a number of compelling reasons why they very probably form a Milky Way halo-mass group at the Lyα redshift. Filamentary structure, possibly consisting of Lyα emission with very high equivalent width, blue stellar continua and evidence for disturbed stellar populations, suggest that the properties of the emitting region reflect ongoing galaxy assembly, with recent galaxy mergers and star formation occurring in the group. The Lyα emission may be powered by cooling radiation or spatially extended star formation in the halo, but is unlikely to be fluorescence driven by either an active galactic nucleus or one of the galaxies. A comparison with the Lyα surface brightness profiles of more typical, bright Lyα emitters or Lyman break galaxies from similarly deep two-dimensional spectra shows them to be conspicuously different from the extended, asymmetric object studied here. This is consistent with the picture that typical Lyα emitters represent Lyα resonantly scattering from single, kinematically quiescent, compact sources of ionizing radiation, whereas extended emission of the kind seen in the current halo reflect a more active, kinematically disturbed stage in the galaxy formation process. Hence, unusual Lyα emission as observed here may provide unique insights into what is probably a key mode of galaxy formation at high redshifts. Our observations provide further, circumstantial evidence that galaxy mergers may promote the production and/or escape of ionizing radiation, and that the haloes of interacting galaxies may be significant sources for ionizing photons during the epoch of reionization.

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Additional Information:© 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2012 November 1. Received 2012 October 26. In original form 2012 June 12. First published online: December 5, 2012. This paper includes data gathered with the 6.5-m Magellan Telescopes located at Las Campanas Observatory, Chile. Some of the data presented herein were 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 the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We acknowledge helpful discussions with Bob Carswell, Hsiao- Wen Chen, Jeff Cooke, Masami Ouchi and Francois Schweizer. We thank the staff of the Las Campanas Observatory and the Keck Observatory for their help with the observations, and thank Luke Barnes for providing us the results of his simulations. MR is grateful to the IoA in Cambridge and to the Raymond and Beverley Sackler Distinguished Visitor programme for hospitality and support in summer 2011, when some of this work was done. He further acknowledges support from the National Science Foundation through grant AST-1108815. GDB has been supported by the Kavli Foundation. J-RG gratefully acknowledges the financial support of a Millikan Fellowship provided by Caltech.
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Kavli FoundationUNSPECIFIED
Caltech Millikan FellowshipUNSPECIFIED
Subject Keywords:galaxies: dwarf – galaxies: evolution – galaxies: interactions – intergalactic medium – dark ages, reionization, first stars – diffuse radiation
Issue or Number:1
Record Number:CaltechAUTHORS:20130613-092001286
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38937
Deposited By: Tony Diaz
Deposited On:24 Jun 2013 16:49
Last Modified:09 Nov 2021 23:41

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