Topic 1: Could quasar lensing time-delays hint to a core component in halos, instead of H0 tension? Topic 2: AGN Variability and HEAN in the age of VRO

Abstract 1: The time delay measured between the images of gravitationally lensed quasars probes a combination of angular diameter distances and the mass profile of the lens. Observational campaigns to measure such systems have reported a determination of the Hubble parameter H0 in tension with determinations based on the cosmic microwave background (CMB) and large scale structure (LSS). I show that a core component in the lens model acts as an approximate mass sheet transformation. This modelling degeneracy was initially not considered by the cosmographic analyses. Including it causes the error budget on H0 to grow, reflecting the uncertainties from stellar kinematics; this effectively eliminates the lensing part of the H0 tension. Time permits, I will also discuss degeneracies between H0 and weak cosmological convergence and shear. Based on 2001.07182, 2105.10873, and work in progress with the same group of authors.

Abstract 2: Over the next ten years, the Vera C. Rubin Observatory (VRO) will observe ∼10 million active galactic nuclei (AGN) with a regular and high cadence. During this time, the intensities of most of these AGN will vary stochastically. Moreover, these fluctuations may also be connected to the high-energy astrophysical neutrino (HEAN) flux observed by IceCube. In this talk, I explore the prospects to quantify these fluctuations with VRO-measurements of AGN light curves and also evaluate the capacity of VRO, in tandem with various current and upcoming neutrino telescopes, to establish AGN as HEAN emitters. I find that AGN variability measurements will be so precise as to allow the AGN to be separated into up to ∼ 10 different correlation-timescale bins. I also show that if the correlation time varies as some power of the luminosity, the normalization and power-law index of that relation will be determined to O(10^{−4}%). Finally, I find that it may be possible to detect AGN contributions at the ~ 3\sigma level to the HEAN flux even if these AGN contribute only ~10% of the HEAN flux.