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The Chandra deep protocluster survey: Lyα blobs are powered by heating, not cooling

Geach, J. E. and Alexander, D. M. and Lehmer, B. D. and Smail, Ian and Matsuda, Y. and Chapman, S. C. and Scharf, C. A. and Ivison, R. J. and Volonteri, M. and Yamada, T. and Blain, A. W. and Bower, R. G. and Bauer, F. E. and Basu-Zych, A. (2009) The Chandra deep protocluster survey: Lyα blobs are powered by heating, not cooling. Astrophysical Journal, 700 (1). pp. 1-9. ISSN 0004-637X.

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We present the results of a 400 ks Chandra survey of 29 extended Lyα emitting nebulae (Lyα Blobs, LABs) in the z = 3.09 protocluster in the SS A22 field. We detect luminous X-ray counterparts in five LABs, implying a large fraction of active galactic nuclei (AGN) in LABs,f_(AGN) = 17^(+12)_( 7)% down to L _(2-32 keV) ~ 10^(44) erg s^(–1). All of the AGN appear to be heavily obscured, with spectral indices implying obscuring column densities of N_ H > 10^(23) cm^(–2). The AGN fraction should be considered a lower limit, since several more LABs not detected with Chandra show AGN signatures in their mid-infrared (mid-IR) emission. We show that the UV luminosities of the AGN are easily capable of powering the extended Lyα emission via photoionization alone. When combined with the UV flux from a starburst component, and energy deposited by mechanical feedback, we demonstrate that "heating" by a central source, rather than gravitational cooling is the most likely power source of LABs. We argue that all LABs could be powered in this manner, but that the luminous host galaxies are often just below the sensitivity limits of current instrumentation, or are heavily obscured. No individual LABs show evidence for extended X-ray emission, and a stack equivalent to a ≳ 9 Ms exposure of an average LAB also yields no statistical detection of a diffuse X-ray component. The resulting diffuse X-ray/Lyα luminosity limit implies there is no hot (T≳10^7 K) gas component in these halos, and also rules out inverse Compton scattering of cosmic microwave background photons, or local far-IR photons, as a viable power source for LABs.

Item Type:Article
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Alexander, D. M.0000-0002-5896-6313
Smail, Ian0000-0003-3037-257X
Bauer, F. E.0000-0002-8686-8737
Additional Information:© 2009. The American Astronomical Society. Received 2009 January 30; accepted 2009 April 8; published 2009 June 30. We thank the referee for helpful comments, and we appreciate useful discussions with Mark Dijkstra, Chris Done, Caryl Gronwall, Cedric Lacey, and Tom Theuns. J.E.G. is funded by the UK Science and Technology Facilities Council (S.T.F.C.). D.M.A. acknowledges the Royal Society and the Leverhulme Trust for financial support. B.D.L. is supported by an S.T.F.C. post-doctoral fellowship. I.S. acknowledges support from the Royal Society and S.T.F.C. Additional support for this work was provided by NASA through Chandra Award Number SAO G07-8138C (S.C.C., C.A.S., M.V.) issued by the Chandra Xray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory under a NASA contract.
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
Leverhulme TrustUNSPECIFIED
Subject Keywords:galaxies: active; galaxies: evolution; galaxies: formation; galaxies: high-redshift; X-rays: galaxies
Record Number:CaltechAUTHORS:20090827-135317395
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Official Citation:The Chandra Deep Protocluster Survey: Lyα Blobs are Powered by Heating, Not Cooling J. E. Geach, D. M. Alexander, B. D. Lehmer, Ian Smail, Y. Matsuda, S. C. Chapman, C. A. Scharf, R. J. Ivison, M. Volonteri, T. Yamada, A. W. Blain, R. G. Bower, F. E. Bauer, and A. Basu-Zych 2009 ApJ 700 1-9 doi: 10.1088/0004-637X/700/1/1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15363
Deposited By: Ruth Sustaita
Deposited On:11 Sep 2009 20:44
Last Modified:31 Oct 2017 22:05

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