AGN Continuum Reverberation Mapping Based on Zwicky Transient Facility Light Curves

Hengxiao Guo, Aaron J. Barth, Shu Wang

Submitted on 13 July 2022


We perform a systematic survey of active galactic nucleus (AGN) continuum lags using 3 day cadence gri-band light curves from the Zwicky Transient Facility. We select a sample of 94 type~1 AGN at z<0.8 with significant and consistent inter-band lags based on the interpolated cross-correlation function method and the Bayesian method JAVELIN. Within the framework of the lamp-post reprocessing model, our findings are: 1) The continuum emission (CE) sizes inferred from the data are larger than the disk sizes predicted by the standard thin disk model; 2) For a subset of the sample, the CE size exceeds the theoretical limit of the self-gravity radius (12 lt-days) for geometrically thin disks; 3) The CE size scales with continuum luminosity as RCEL0.48±0.04 with a scatter of 0.2 dex, analogous to the well-known radius-luminosity relation of broad Hβ. These findings suggest a significant contribution of diffuse continuum emission from the broad-line region (BLR) to AGN continuum lags. We find that the RCEL relation can be explained by a photoionization model that assumes 23% of the total flux comes from the diffuse BLR emission. In addition, the ratio of the CE size and model-predicted disk size anti-correlates with the continuum luminosity, indicative of a potential non-disk BLR lag contribution evolving with luminosity. Finally, a robust positive correlation between CE size and black hole mass is detected.


Comment: 25 pages, 11 figures, 4 tables. Submitted to ApJ, comments welcome

Subject: Astrophysics - Astrophysics of Galaxies