2010/05/25 by Z. Y. Zheng, Zhen-Ya Zheng, J. X. Wang +9
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Chandra Deep Field South #Emission spectrum #Equivalent width #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Hubble Deep Field #Luminosity #Luminosity function #Physics #Quasar #Redshift #Spectral line #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.1088/0004-637x/718/1/52
12 pages, 5 figures, ApJ accepted
arxiv created 2010/05/25 · openalex publication_date 2010/06/25 · arxiv updated 2015/05/19 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We report the first X-ray detection of Lyα emitters (LAEs) at redshift z ∼ 4.5. One source (J033127.2-274247) is detected in the Extended Chandra Deep Field-South (ECDF-S) X-ray data and has been spectroscopically confirmed as a z = 4.48 quasar with L X = 4.2 × 10 44 erg s −1 . The single detection gives an Lyα quasar density of ∼ 2.7 +6.2 −2.2 × 10 −6 Mpc −3 , consistent with the X-ray luminosity function of quasars. Another 22 LAEs in the central Chandra Deep Field-South region are not detected individually, but their co-added counts yield an S/N = 2.4 ( p = 99.83%) detection at soft band, with an effective exposure time of ∼36 Ms. Further analysis of the equivalent width (EW) distribution shows that all the signals come from 12 LAE candidates with EW rest < 400 Å and 2 of them contribute about half of the signal. From follow-up spectroscopic observations, we find that one of the two is a low-redshift emission-line galaxy, and the other is a Lyman break galaxy at z = 4.4 with little or no Lyα emission. Excluding these two and combined with ECDF-S data, we derive a 3σ upper limit on the average X-ray flux of F 0.5–2.0 keV < 1.6 × 10 −18 erg cm −2 s −1 , which corresponds to an average luminosity of 〈 L 0.5–2 keV 〉 <2.4 × 10 42 erg s −1 for z ∼ 4.5 LAEs. If the average X-ray emission is due to star formation, it corresponds to a star formation rate (SFR) of <180–530 M ☉ yr −1 . We use this SFR X as an upper limit of the unobscured SFR to constrain the escape fraction of Lyα photons and find a lower limit of f esc,Lyα > 3%–10%. However, our upper limit on the SFR X is ∼7 times larger than the upper limit on SFR X on z ∼ 3.1 LAEs in the same field and at least 30 times higher than the SFR estimated from Lyα emission. From the average X-ray-to-Lyα line ratio, we estimate that fewer than 3.2% (6.3%) of our LAEs could be high-redshift type 1 (type 2) active galactic nuclei (AGNs) and those hidden AGNs likely show low rest-frame EWs.