Variability-selected Low-luminosity Active Galactic Nuclei Candidates in the 7 Ms Chandra Deep Field-South

Journal
Date Issued
2018
Author(s)
Ding, N.
•
Luo, B.
•
Brandt, W. N.
•
•
Yang, G.
•
Lehmer, B. D.
•
Shemmer, O.
•
Schneider, D. P.
•
•
Xue, Y. Q.
•
Zheng, X. C.
•
Gu, Q. S.
•
Koekemoer, A. M.
•
Vignali, C.
•
•
Wang, J. X.
DOI
Abstract
In deep X-ray surveys, active galactic nuclei (AGNs) with a broad range of luminosities have been identified. However, cosmologically distant low-luminosity AGN (LLAGN, {L}{{X}}≲ {10}42 erg s-1) identification still poses a challenge because of significant contamination from host galaxies. Based on the 7 Ms Chandra Deep Field-South (CDF-S) survey, the longest-timescale (∼17 years) deep X-ray survey to date, we utilize an X-ray variability selection technique to search for LLAGNs that remain unidentified among the CDF-S X-ray sources. We find 13 variable sources from 110 unclassified CDF-S X-ray sources. Except for one source that could be an ultraluminous X-ray source, the variability of the remaining 12 sources is most likely due to accreting supermassive black holes. These 12 AGN candidates have low intrinsic X-ray luminosities, with a median value of 7 × 1040 erg s-1. They are generally not heavily obscured, with an average effective power-law photon index of 1.8. The fraction of variable AGNs in the CDF-S is independent of X-ray luminosity and is only restricted by the total number of observed net counts, confirming previous findings that X-ray variability is a near-ubiquitous property of AGNs over a wide range of luminosities. There is an anticorrelation between X-ray luminosity and variability amplitude for high-luminosity AGNs, but as the luminosity drops to ≲1042 erg s-1, the variability amplitude no longer appears dependent on the luminosity. The entire observed luminosity-variability trend can be roughly reproduced by an empirical AGN variability model based on a broken power-law power spectral density function.
Volume
868
Issue
2
Start page
88
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2018ApJ...868...88D
Rights
open.access
File(s)
Loading...
Thumbnail Image
Name

Ding_2018_ApJ_868_88.pdf

Description
Pdf editoriale
Size

2.13 MB

Format

Adobe PDF

Checksum (MD5)

86e421001ac1da59d78d7aa21cbcdea9