Toward measuring supermassive black hole masses with interferometric observations of the dust continuum

This work focuses on active galactic nuclei (AGNs) and on the relation between the sizes of the hot dust continuum and the broad-line region (BLR). We find that the continuum size measured using optical/near-infrared interferometry (OI) is roughly twice that measured by reverberation mapping (RM). Both OI and RM continuum sizes show a tight relation with the H beta BLR size, with only an intrinsic scatter of 0.25 dex. The masses of supermassive black holes (BHs) can hence simply be derived from a dust size in combination with a broad line width and virial factor. Since the primary uncertainty of these BH masses comes from the virial factor, the accuracy of the continuum-based BH masses is close to those based on the RM measurement of the broad emission line. Moreover, the necessary continuum measurements can be obtained on a much shorter timescale than those required monitoring for RM, and they are also more time efficient than those needed to resolve the BLR with OI. The primary goal of this work is to demonstrate a measuring of the BH mass based on the dust-continuum size with our first calibration of the R-BLR-R-d relation. The current limitation and caveats are discussed in detail. Future GRAVITY observations are expected to improve the continuum-based method and have the potential of measuring BH masses for a large sample of AGNs in the low-redshift Universe.

Automated summary

This work focuses on the relation between sizes of the hot dust continuum and the broad-line region (BLR) in active galactic nuclei (AGNs). The study shows that the continuum size measured using optical/near-infrared interferometry is roughly twice that measured by reverberation mapping. Both methods show a tight relation between continuum sizes and the H beta BLR size, allowing for the derivation of supermassive black hole (BH) masses with good accuracy. The study also highlights the advantages of continuum-based measurements over traditional methods in terms of time efficiency.