RESEARCH / 02
Quasars at the extremes
The Cosmic Himalayas and the environments of black-hole growth
Quasars are powered by accretion onto supermassive black holes. I study their environments by comparing the spatial distributions of quasars, galaxies, and intergalactic hydrogen, with a particular focus on the Cosmic Himalayas at z ≈ 2.2.
An extreme environment
Our 2025 study identified a concentration of 11 quasars at z = 2.16–2.20 in the BOSSJ0210 field. It was the highest quasar density peak identified within the study’s approximately 10,000-square-degree SDSS search. Subaru imaging and absorption in background-quasar spectra provided complementary maps of the surrounding galaxies and gas.
Three tracers, different structures
The quasar concentration does not coincide with the peaks in galaxy density or hydrogen absorption. Instead, it lies near the boundary between more opaque and more transparent gas. These spatial differences motivate questions about black-hole fueling and ionizing radiation; the maps alone do not establish a causal feedback mechanism.
Connecting observations with simulations
In a collaborative follow-up using the CROCODILE simulation, we examined how rare such quasar concentrations are. Accounting for the non-Gaussian distribution of overdensities reduces their apparent rarity and reconciles Cosmic Himalayas-like structures with the standard ΛCDM framework.
References
Cosmic Himalayas in CROCODILE: Probing the Extreme Quasar Overdensities by Count-in-cells Analysis and Nearest-neighbor Distribution
ApJ, 1001, 172
Cosmic Himalayas: The Highest Quasar Density Peak Identified in a 10,000 deg² Sky with Spatial Discrepancies between Galaxies, Quasars, and IGM H I
ApJ, 986, 60