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Probing AGN structure using microlensing from z = 0.5 to z = 4.5
Program ID 19037
Science Category Active Galaxies & Supermassive Black Holes
Program Type Analysis
Category Small
Principal Investigator Padmavathi Venkatraman
PI Institution University of Illinois Urbana Champaign
Co-Investigators
  • Yue Shen (University of Illinois, Urbana-Champaign)
  • Timo Anguita (Astrophysics Institute of Universidad AndrĂ©s Bello)
  • Martin Millon (University of Geneva)
  • Phil Marshall (Kavli Institute for Particle Astrophysics and Cosmology, Stanford)
  • Paras Sharma (State University of New York, Stony Brook)
  • Henry Best (Masaryk University)
  • Simon Birrer (State University of New York, Stony Brook)
  • Sydney Erickson (Kavli Institute for Particle Astrophysics and Cosmology, Stanford)
  • Tommaso Treu (University of California, Los Angeles)
Abstract Probing Active Galactic Nuclei (AGN) structure is important to understanding fundamental AGN accretion physics, black hole growth, AGN-host galaxy evolution and feedback mechanisms. In this study, we propose to use microlensing of AGN to probe AGN structure. Gravitationally lensed quasars undergo two types of lensing: macrolensing from the foreground galaxy and microlensing by stars in the foreground galaxy. While macrolensing is an achromatic effect, microlensing is chromatic based on which region of the background quasar is lensed by stars in the foreground galaxy. So far, measuring flux ratios between the lensed images in different optical bands has laid the road to measuring the accretion disk sizes. We propose to extend this further into the near-infrared (NIR) and utilize Roman imaging to probe the parts of the quasar emitting in the NIR such as the outer regions of the accretion disk to inner edge of the torus, thus building a comprehensive UV-Optical-NIR view of AGN structure. We forecast that ~300 lensed quasars, with quasars in between redshifts 0.5 to 4.5, will overlap in Rubin and Roman. Using this statistically significant sample, we can place competitive constraints on the outer portions of the accretion disk and understand where the torus begins out to cosmological redshifts. We also plan to use grism spectroscopy for 40 systems to use flux ratios of H-beta broad line feature from the broad-line emitting region (BLR) and measure Balmer-line BLR size at z > 1, which has never been done on a statistical sample.