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X-Ray Nondetection of the Lyα Emitters at z ~ 4.5

2004; IOP Publishing; Volume: 608; Issue: 1 Linguagem: Inglês

10.1086/422311

1538-4357

J. X. Wang, James E. Rhoads, Sangeeta Malhotra, Steve Dawson, Daniel Stern, Arjun Dey, Timothy M. Heckman, Colin Norman, Hyron Spinrad,

Astrophysics and Cosmic Phenomena

The Lyα emitters found at z ∼ 4.5 by the Large Area Lyman Alpha (LALA) survey have high equivalent widths in the Lyα line, which can be produced by either narrow-lined active galactic nuclei (AGNs) or by stellar populations with a very high proportion of young, massive stars.To investigate the AGN scenario, we obtained two deep Chandra exposures to study the X-ray nature of the Lyα emitters.The 172 ks deep Chandra image on the LALA Boötes field was presented in a previous paper (Malhotra et al. 2003), and in this paper we present a new Chandra deep exposure (174 ks) on the LALA Cetus field, which doubled our sample of X-ray imaged Lyα sources, and imaged the brightest source among our Lyα emitters.None of the 101 Lyα sources covered by two Chandra exposures was detected individually in X-ray, with a 3σ limiting X-ray flux of F 0.5-10.0keV< 3.3 × 10 -16 ergs cm -2 s -1 for on-axis targets.The sources remain undetectable in the stacked image, implying a 3σ limit to the average luminosity of L 2-8keV < 2.8 × 10 42 ergs s -1 .The resulting X-ray to Lyα ratio is > 21 times lower than the ratios for known high redshift type-II quasars.Together with optical spectra obtained at Keck, we conclude that no evidence of AGN activity was found among our Lyα emitters at z ∼ 4.5.