Program: GN-2021B-DD-101

The duration of quasar (QSO) accretion episodes is a key quantity for distinguishing between models for supermassive black hole (SMBH) growth, QSO evolution, and QSO feedback effects. However, this critical timescale, the so-called QSO lifetime t_Q, is still uncertain by orders of magnitude. The QSO's UV radiation ionizes the surrounding gas, which is observable as enhanced Lyman-alpha transmission in the QSO's so-called proximity zone. The size of the HeII proximity zone probed by HST/COS depends sensitively on the QSO lifetime for t_Q<30Myr, comparable to the e-folding timescale for SMBH growth (45Myr). Comparing the sizes of archival HeII proximity zones to 1D radiative transfer simulations, we inferred individual lifetimes to 0.2dex precision for QSOs with precise redshifts from near-IR spectroscopy. These data revealed a surprisingly broad distribution of lifetimes from <1 to >30Myr, indicating complex QSO lightcurves. We are conducting an HST/COS survey of 32 QSOs to double the number of QSOs to which we can apply this exciting technique, which will enable the first measurement of the QSO lifetime distribution. To fully leverage our HST data, we were granted a joint HSTNOIRLab program to measure the systemic redshifts and SMBH masses of our targets with Gemini near-Infrared spectroscopy. Here we aim to move forward with our program that started in 2021A.