ar X iv : a st ro - p h / 04 04 61 1 v 1 3 0 A pr 2 00 4 X - ray nondetection of the Ly α Emitters at z ∼ 4 . 5
نویسندگان
چکیده
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.
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