The deepest X-ray view of high-redshift galaxies : Constraints on low-rate black hole accretion

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DOI:
| Published | English
Authors:
Vito, F. ; Gilli, R. ; Vignali, C. ; Brandt, W. N. ; Comastri, A. ; Yang, G. ; Lehmer, B. D. ; Luo, B. ; Basu-Zych, A. ; Bauer, F. E. ; Cappelluti, N. ; Koekemoer, A.
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Department:
Lund Observatory - Has been reorganised
Abstract:

We exploit the 7 Ms Chandra observations in the Chandra Deep Field-South (CDF-S), the deepest X-ray survey to date, coupled with CANDELS/GOODS-S data, to measure the total X-ray emission arising from 2076 galaxies at 3.5 ≤ z < 6.5. This aim is achieved by stacking the Chandra data at the positions of optically selected galaxies, reaching effective exposure times of ≥109s.We detect significant (>3.7s) X-ray emission from massive galaxies at z ≈ 4. We also report the detection of massive galaxies at z ≈ 5 at a 99.7 per cent confidence level (2.7σ), the highest significance ever obtained for X-ray emission from galaxies at such high redshifts. No significant signal is detected from galaxies at even higher redshifts. The stacking results place constraints on theBHADassociated with the known high-redshift galaxy samples, as well as on the SFRD at high redshift, assuming a range of prescriptions for X-ray emission due to X- ray binaries.We find that the X-ray emission from our sample is likely dominated by processes related to star formation. Our results show that low-rate mass accretion on to SMBHs in individually X-ray-undetected galaxies is negligible, compared with the BHAD measured for samples of X-ray detected AGN, for cosmic SMBH mass assembly at high redshift. We also place, for the first time, constraints on the faint-end of the AGN X-ray luminosity function (logLX ~ 42) at z > 4, with evidence for fairly flat slopes. The implications of all of these findings are discussed in the context of the evolution of the AGN population at high redshift.

Keywords:
Galaxies: active ; Galaxies: evolution ; Galaxies: high ; methods: data analysis ; Redshift ; Surveys ; X-rays: galaxies
ISSN:
0035-8711
LUP-ID:
df1a61c3-4f01-4bb6-a070-15085b567d1d | Link: https://lup.lub.lu.se/record/df1a61c3-4f01-4bb6-a070-15085b567d1d | Statistics

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