What powers Ly alpha blobs?
Résumé
Ly alpha blobs (LABs) are spatially extended Ly alpha nebulae seen at high redshift. The origin of Ly alpha 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 mu Jy and 77 +/- 16 mu Jy, respectively, and B5 is marginally detected at 3 sigma (51 +/- 16 mu Jy). 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(-0:35)(+0:30) for B6 and 2.20(-0:30)(+0:45) for B7, which are consistent with the redshift of the Ly alpha 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 Ly alpha 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.