What powers Lyα blobs?^⋆

¹ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, 181-8588 Tokyo, Japan
e-mail: yiping.ao@nao.ac.jp
² Purple Mountain Observatory, Chinese Academy of Sciences, 210008 Nanjing, PR China
³ Institut d′Astrophysique Spatiale, Bât. 121, Université Paris-Sud, 91405 Orsay Cedex, France
⁴ MPIfR, Auf dem Hügel 69, 53121 Bonn, Germany
⁵ Astron. Dept., King Abdulaziz Univ., PO Box 80203, 21589 Jeddah, Saudi Arabia
⁶ Princeton University Observatory, Princeton, NJ 08544, USA
⁷ European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany
⁸ Research School of Astronomy and Astrophysics, The Australian National University, Canberra ACT 0200, Australia
⁹ California Institute of Technology 301-17, 1200 E. California Blvd, Pasadena, CA 91125, USA
¹⁰ Aix Marseille Université, CNRS, LAM (Laboratoire d′Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
¹¹ Institut d′Astrophysique de Paris, CNRS and Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France
¹² School of Mathematics and Physics, University of Tasmania, Private Bag 37 Hobart, 7001, Australia
¹³ Joint Institute for VLBI, Postbus 2, 7990 AA Dwingeloo, The Netherlands
¹⁴ Australia Telescope National Facility, CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
¹⁵ Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA

Received: 9 May 2014
Accepted: 20 July 2015

Abstract

Lyα blobs (LABs) are spatially extended Lyα  nebulae seen at high redshift. The origin of Lyα emission in the LABs is still unclear and under debate. To study their heating mechanism(s), we present Australia Telescope Compact Array (ATCA) observations of the 20 cm radio emission and Herschel PACS and SPIRE measurements of the far-infrared (FIR) emission toward the four LABs in the protocluster J2143-4423 at z = 2.38. Among the four LABs, B6 and B7 are detected in the radio with fluxes of 67±17 μJy and 77±16 μJy, respectively, and B5  is marginally detected at 3σ (51±16 μJy). For all detected sources, their radio positions are consistent with the central positions of the LABs. Among them, B6 and B7 are obviously also detected in the FIR. By fitting the data with different templates, we obtained redshifts of 2.20^+0.30_-0.35 for B6 and 2.20^+0.45_-0.30 for B7, which are consistent with the redshift of the Lyα emission within uncertainties, indicating that both FIR sources are likely associated with the LABs. The associated FIR emission in B6 and B7 and high star formation rates strongly favor star formation in galaxies as an important powering source for the Lyα emission in both LABs. However, the other two, B1 and B5, are predominantly driven by the active galactic nuclei or other sources of energy still to be specified, but not mainly by star formation. In general, the LABs are powered by quite diverse sources of energy.