No X-ray-bright type II quasars among the Lyα emitters

The Lyalpha emitters found at z = 4.5 and 5.7 by the Large Area Lyman Alpha (LALA) survey have high equivalent widths in the Lyalpha line. Such lines can be produced by narrow-lined active galactic nuclei or by stellar populations with a very high proportion of young massive stars. To check for type II (i.e., narrow-lined) quasars, we obtained a deep X-ray image of 49 Lyalpha sources in a single field of the ACIS instrument on the Chandra X-Ray Observatory. None of these sources was detected with a 3 sigma limiting X-ray luminosity of 2.9 X 10(43) ergs s(-1). For comparison, the two known high-redshift type II quasars have luminosities of 4 X 10(43) ergs s(-1) before extinction correction. The sources remain undetected in stacked images of the 49 Lyalpha sources (with 6.5 Ms effective Chandra on-axis exposure) at 3 sigma limits of 4.0 X 10(42). The resulting X-ray-to-Lyalpha ratio is about 4-24 times lower than the ratio for known type II quasars, while the average Lyalpha luminosity of the LALA sample is between the two type II's. The cumulative X-ray-to-Lyalpha ratio limit is also below that of 90% of low-redshift Seyfert galaxies.