Evolution of the Lyman-alpha Halos around High-Redshift Radio Galaxies

Abstract

We have obtained the first constraints on extended Ly-alpha emission at z ~ 1 in a sample of five radio galaxies. We detect Ly-alpha emission from four of the five galaxies. The Ly-alpha luminosities range from 0.1 - 4 times 10^43 erg/s and are much smaller than those observed for halos around higher redshift radio galaxies. If the z ~ 1 radio galaxies are the descendents the z >~ 2 radio galaxies, then their Ly-alpha luminosities evolve strongly with redshift as ~(1+z)^5. There do not appear to be strong correlations between other parameters, such as radio power, suggesting that this observed evolution is real and not an observational artifact or secondary correlation. We speculate that this evolution of luminous halos may be due to gas depletion (as gas cools, settles, and forms stars) accompanied by an overall rise in the mean gas temperature and a decrease in specific star-formation rate in and around these massive galaxies.

5 pages, 4 figures, published in ApJ Letters, 694, L31-35 March 20 2009

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• A Successful Broad-band Survey for Giant Lya Nebulae II: Spectroscopic Confirmation
• The nature of faint radio galaxies at high redshifts
• Lyman Alpha and MgII as Probes of Galaxies and their Environments
• Where is the fuzz? Undetected Lyman alpha nebulae around QSOs at z~2.3
• The disappearance of Lyman alpha blobs: a GALEX search at z=0.8
• Inverse Compton X-ray halos around high-z radio galaxies: A feedback mechanism powered by far-infrared starbursts or the CMB?