X-RAY PROPERTIES OF THE z {approx} 4.5 Ly{alpha} EMITTERS IN THE CHANDRA DEEP FIELD SOUTH REGION

Journal Article · Tue Jul 20 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/718/1/52· OSTI ID:21455168

Zheng, Z Y; Wang, J X ^[1]; Finkelstein, S L; Finkelstein, K D ^[2]; Malhotra, S

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1. Center for Astrophysics, University of Science and Technology of China, Hefei, Anhui 230026 (China)
2. George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States)

We report the first X-ray detection of Ly{alpha} emitters (LAEs) at redshift z {approx} 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{sub X} = 4.2 x 10{sup 44} erg s{sup -1}. The single detection gives an Ly{alpha} quasar density of {approx} 2.7{sup +6.2} {sub -2.2} x 10{sup -6} Mpc{sup -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 {approx}36 Ms. Further analysis of the equivalent width (EW) distribution shows that all the signals come from 12 LAE candidates with EW{sub rest}< 400 A 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 Ly{alpha} emission. Excluding these two and combined with ECDF-S data, we derive a 3{sigma} upper limit on the average X-ray flux of F {sub 0.5-2.0keV} < 1.6 x 10{sup -18} erg cm{sup -2} s{sup -1}, which corresponds to an average luminosity of (L {sub 0.5-2keV}) <2.4 x 10{sup 42} erg s{sup -1} for z {approx} 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 {sub sun} yr{sup -1}. We use this SFR {sub X} as an upper limit of the unobscured SFR to constrain the escape fraction of Ly{alpha} photons and find a lower limit of f{sub esc,Ly{alpha}} > 3%-10%. However, our upper limit on the SFR {sub X} is {approx}7 times larger than the upper limit on SFR {sub X} on z {approx} 3.1 LAEs in the same field and at least 30 times higher than the SFR estimated from Ly{alpha} emission. From the average X-ray-to-Ly{alpha} 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.

• OSTI ID: 21455168
• Journal Information: Astrophysical Journal, Vol. 718, Issue 1; Other Information: DOI: 10.1088/0004-637X/718/1/52; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
EMISSION
GALAXY NUCLEI
LUMINOSITY
PHOTONS
QUASARS
RED SHIFT
STARS
X-RAY DETECTION
X-RAY GALAXIES
BOSONS
COSMIC RADIO SOURCES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
DETECTION
ELEMENTARY PARTICLES
GALAXIES
MASSLESS PARTICLES
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATION DETECTION