ATTENZIONE! IL REPOSITORY E’ APERTO ESCLUSIVAMENTE ALL’IMMISSIONE DEI RAPPORTI TECNICI (COLLEZIONE 4.01). NON E’ POSSIBILE INSERIRE PRODOTTI IN TUTTE LE ALTRE COLLEZIONI, A CAUSA DI PROBLEMI TECNICI. THE REPOSITORY IS OPEN EXCLUSIVELY FOR THE SUBMISSION OF TECHNICAL REPORTS (COLLECTION 4.01). SUBMISSIONS TO ALL OTHER COLLECTIONS ARE TEMPORARILY UNAVAILABLE, DUE TO TECHNICAL ISSUES.
 

A High Space Density of L* Active Galactic Nuclei at z ̃ 4 in the COSMOS Field

Journal
Date Issued
2018
Author(s)
Boutsia, K.
•
•
•
•
Civano, F.
DOI
Abstract
Identifying the source population of ionizing radiation, responsible for the reionization of the universe, is currently a hotly debated subject with conflicting results. Studies of faint, high-redshift star-forming galaxies, in most cases, fail to detect enough escaping ionizing radiation to sustain the process. Recently, the capacity of bright quasi-stellar objects to ionize their surrounding medium has been confirmed also for faint active galactic nuclei (AGNs), which were found to display an escaping fraction of ̃74% at z ̃ 4. Such levels of escaping radiation could sustain the required UV background, given the number density of faint AGNs is adequate. Thus, it is mandatory to accurately measure the luminosity function of faint AGNs (L ̃ L*) in the same redshift range. For this reason we have conducted a spectroscopic survey, using the wide field spectrograph IMACS at the 6.5 m Baade Telescope, to determine the nature of our sample of faint AGN candidates in the COSMOS field. This sample was assembled using photometric redshifts, color, and X-ray information. We ended up with 16 spectroscopically confirmed AGNs at 3.6< z< 4.2 down to a magnitude of i AB = 23.0 for an area of 1.73 deg2. This leads to an AGN space density of ̃ 1.6× {10}-6{Mpc}}-3 (corrected) at z ̃ 4 for an absolute magnitude of M 1450 = -23.5. This is higher than previous measurements and seems to indicate that AGNs could make a substantial contribution to the ionizing background at z ̃ 4. Assuming that AGN physical parameters remain unchanged at higher redshifts and fainter luminosities, these sources could be regarded as the main drivers of cosmic reionization.
Volume
869
Issue
1
Start page
20
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2018ApJ...869...20B
Rights
open.access
File(s)
Loading...
Thumbnail Image
Name

Boutsia_2018_ApJ_869_20.pdf

Description
Pdf editoriale
Size

1.74 MB

Format

Adobe PDF

Checksum (MD5)

47c2f46d0ce892e245226620ebea4b40