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Published June 20, 2012 | Published
Journal Article Open

Resolving the Galaxies within a Giant Lyα Nebula: Witnessing the Formation of a Galaxy Group?


Detailed analysis of the substructure of Lyα nebulae can put important constraints on the physical mechanisms at work and the properties of galaxies forming within them. Using high-resolution Hubble Space Telescope (HST) imaging of a Lyα nebula at z ≈ 2.656, we have taken a census of the compact galaxies in the vicinity, used optical/near-infrared colors to select system members, and put constraints on the morphology of the spatially extended emission. The system is characterized by (1) a population of compact, low-luminosity (~0.1 L*) sources—17 primarily young, small (R_e ≈ 1-2 kpc), disky galaxies including an obscured active galactic nucleus—that are all substantially offset (≳20 kpc) from the line-emitting nebula; (2) the lack of a central galaxy at or near the peak of the Lyα emission; and (3) several nearly coincident, spatially extended emission components—Lyα, He II, and UV continuum—that are extremely smooth. These morphological findings are difficult to reconcile with theoretical models that invoke outflows, cold flows, or resonant scattering, suggesting that while all of these physical phenomena may be occurring, they are not sufficient to explain the powering and large extent of Lyα nebulae. In addition, although the compact galaxies within the system are irrelevant as power sources, the region is significantly overdense relative to the field galaxy population (by at least a factor of four). These observations provide the first estimate of the luminosity function of galaxies within an individual Lyα nebula system and suggest that large Lyα nebulae may be the seeds of galaxy groups or low-mass clusters.

Additional Information

© 2012 American Astronomical Society. Received 2011 May 25; accepted 2012 April 11; published 2012 May 30. The authors thank Kate Brand, Galina Soutchkova, and SangeetaMalhotra for their assistance with the HST observation planning and execution. We are grateful to Crystal Martin, Kristian Finlator, Avi Loeb, Dan Weedman, Tommaso Treu, Matt Auger, and the anonymous referee for useful discussions and suggestions. M.K.M.P. acknowledges support from an NSF Graduate Research Fellowship, a P.E.O. Fellowship, and a TABASGO Prize Postdoctoral Fellowship. This work was based on observations made with the NASA/ESA Hubble Space Telescope (HST Cycle 14; GO#10591), obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work is also based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and on data from the NOAO Deep Wide-Field Survey (B. Jannuzi, A. Dey) as distributed by the NOAO Science Archive. A.D. and B.T.J.'s research activities are supported by NOAO. NOAO is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under a cooperative agreement with the National Science Foundation. V.D. and B.T.S. are supported by the Spitzer Space Telescope project, which is managed by JPL on behalf of NASA. Facilities: HST, Subaru, Mayall

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