# # Program information file # PROGRAM_ID 2022A050 PROGRAM_TITLE Infrared Spectroscopic Reverberation Mapping of two GRAVITY/VLTI-targeted Active Galactic Nuclei PROGRAM_INV1 Tommaso Treu PROGRAM_INV2 Vardha Bennert PROGRAM_INV3 Michael Brotherton PROGRAM_INV4 Hermine Landt PROGRAM_INV5 Jan-Min Wang PROGRAM_SCICAT extra-galactic PROGRAM_ABSTRACT_BEG The broad line region [BLR] is the key to understanding supermassive black holes, how they work, grow and evolve. It provides the best [often the only] measures of black hole mass and the geometry of its surroundings. We propose to obtain transformative new insights into the BLRs of two nearby AGNs by carrying out a reverberation mapping [RM] campaign of the same near infrared emission lines [Br gamma, Pa alpha and Pa beta] for which the new instrument GRAVITY on VLT is providing spatially resolved spectroastrometry [SA]. The immediate goal of this proposal is to combine the two probes to map the geometry and kinematics of the BLR, determine the black hole mass, and measure the absolute distance to the AGNs. Once the precision and accuracy of the distance measurement has been established, the long term is to use the two combined probes [SARM] to measure the Hubble constant, independent of all other methods. PROGRAM_ABSTRACT_END