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, LX ≲ 10 42 erg s-1) identification still poses a challenge because of significant contamination from host galaxies. Based on the 7Ms 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.

Ding, N., Luo, B., Brandt, W., Paolillo, M., Yang, G., Lehmer, B., et al. (2018). Variability-selected Low-luminosity Active Galactic Nuclei Candidates in the 7 Ms Chandra Deep Field-South. THE ASTROPHYSICAL JOURNAL, 868(2), 1-17 [10.3847/1538-4357/aaea60].

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

Vignali, C.
Membro del Collaboration Group
;
2018

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, LX ≲ 10 42 erg s-1) identification still poses a challenge because of significant contamination from host galaxies. Based on the 7Ms 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.
2018
Ding, N., Luo, B., Brandt, W., Paolillo, M., Yang, G., Lehmer, B., et al. (2018). Variability-selected Low-luminosity Active Galactic Nuclei Candidates in the 7 Ms Chandra Deep Field-South. THE ASTROPHYSICAL JOURNAL, 868(2), 1-17 [10.3847/1538-4357/aaea60].
Ding, N.; Luo, B.; Brandt, W.N.; Paolillo, M.; Yang, G.; Lehmer, B.D.; Shemmer, O.; Schneider, D.P.; Tozzi, P.; Xue, Y.Q.; Zheng, X.C.; Gu, Q.S.; Koek...espandi
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/673784
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