Variability Selected Low-Luminosity Active Galactic Nuclei in the 4 Ms Chandra Deep Field-South
- Author:
- Schneider, D. P.
- Published:
- January 2012.
- Physical Description:
- 1 electronic document
- Additional Creators:
- Brandt, W. N.
Lehmer, B. D.
Alexander, F. E.
Shemmer, O.
Xue, Y. Q.
Young, M.
Paolillo, D. M.
Bauer, F. E.
Vignail, C.
Luo, B. - Access Online:
- hdl.handle.net
- Restrictions on Access:
- Unclassified, Unlimited, Publicly available.
- Summary:
- The 4 Ms Chandra Deep Field-South (CDF-S) and other deep X-ray surveys have been highly effective at selecting active galactic nuclei (AGN). However, cosmologically distant low-luminosity AGN (LLAGN) have remained a challenge to identify due to significant contribution from the host galaxy. We identify long-term X ray variability (approx. month years, observed frame) in 20 of 92 CDF-S galaxies spanning redshifts approx equals 00.8 - 1.02 that do not meet other AGN selection criteria. We show that the observed variability cannot be explained by X-ray binary populations or ultraluminous X-ray sources, so the variability is most likely caused by accretion onto a supermassive black hole. The variable galaxies are not heavily obscured in general, with a stacked effective power-law photon index of Gamma(sub Stack) approx equals 1.93 +/- 0.13, and arc therefore likely LLAGN. The LLAGN tend to lie it factor of approx equal 6-89 below the extrapolated linear variability-luminosity relation measured for luminous AGN. This may he explained by their lower accretion rates. Variability-independent black-hole mass and accretion-rate estimates for variable galaxies show that they sample a significantly different black hole mass-accretion-rate space, with masses a factor of 2.4 lower and accretion rates a factor of 22.5 lower than variable luminous AGNs at the same redshift. We find that an empirical model based on a universal broken power-law power spectral density function, where the break frequency depends on SMBH mass and accretion rate, roughly reproduces the shape, but not the normalization, of the variability-luminosity trends measured for variable galaxies and more luminous AGNs.
- Collection:
- NASA Technical Reports Server (NTRS) Collection.
- Note:
- Document ID: 20120009483.
GSFC.JA.6055.2012. - Terms of Use and Reproduction:
- Copyright, Distribution under U.S. Government purpose rights.
- Access Online:
- hdl.handle.net
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