Oral Presentation

Tracing quasar activity histories with proximity zones in DESI Y1

Author(s): Ryuichiro Hada (ASIAA), Paul Martini (The Ohio State University), David H. Weinberg (The Ohio State University), Zheng Zheng (The University of Utah), on behalf of the DESI Collaboration

Presenter: Ryuichiro Hada (ASIAA)

The intergalactic medium (IGM) around quasars is shaped by both their dense environments and excess ionizing radiation, forming a "quasar proximity zone" whose size and anisotropy depend on the quasar halo mass, luminosity, age, and radiation geometry. Using over 10,000 quasar pairs from the Dark Energy Spectroscopic Instrument (DESI) Year 1 data, with projected comoving separations below 2 Mpc/h, we investigate how foreground quasars at z ~ 2–3.5 affect Lyman-alpha absorption in background quasar sightlines. The large DESI sample enables precise measurements of the transverse proximity effect and its dependence on projected separation and foreground quasar luminosity.
We find that enhanced gas clustering near quasars dominates over their ionizing effect, leading to stronger absorption on neighboring sightlines. Assuming isotropic and steady ionizing emission, we infer the IGM overdensity profile around quasars and find overdensities as high as ~10 at comoving distances of ~1 Mpc/h from the most luminous systems. Surprisingly, we find no significant dependence of the proximity profile on foreground quasar luminosity. This lack of luminosity dependence may reflect a cancellation between higher ionizing flux and higher gas overdensity, or it may indicate highly time-variable or anisotropic quasar emission, such that the observed luminosity does not trace the ionizing flux along nearby sightlines. These results show that quasar proximity statistics provide a population-level probe of supermassive black hole activity histories on Myr timescales, complementary to luminosity-based AGN studies.