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Weather in Bologna

Bologna
November 22, 2017, 1:53 pm
Sunny
Sunny
13°C
real feel: 15°C
current pressure: 1020 mb
humidity: 62%
wind speed: 0 m/s N
sunrise: 7:20 am
sunset: 4:42 pm
 
Seminars

Thursday Seminars

Tuesday, July 26th, at 15:00, in Sala Seminari:

 

Fabio Vito

(The Pennsylvania State University, US)

 

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

 

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. The stacking results place constraints on the BHAD associated with the known high-redshift galaxy samples, as well as constraining the SFRD at high redshift. 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 onto 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 (logL_X~42) at z>4, with evidence for fairly flat slopes. This is in contrast with recent findings which implied a significant contribution of AGN to the cosmic Reionization.