Year: 2026
Type: preprint
Abstract: The discovery of Little Red Dots (LRDs) with JWST provides a new source population for cosmology in a largely unmapped period of cosmic history. LRDs are most numerous at $4\lesssim z\lesssim9$, thereby bridging existing low-redshift large-scale-structure measurements and the cosmic microwave background. In this epoch, the Universe is deep in the matter-dominated era, where dark energy is dynamically negligible and the expansion history is tightly predicted in $Λ$CDM, making these redshifts a clean test of the standard cosmological model. Recent measurements indicate that LRDs have number densities of $\bar n\sim10^{-4}$ $h^3$ Mpc$^{-3}$, a bias rising from $b\sim 3$ to $\sim8$ over this interval, and distinctive spectrophotometric signatures -- a remarkably favorable combination for baryon acoustic oscillation (BAO) measurements. Using a Fisher forecast with these fiducial inputs, we find that a wide-field spectroscopic survey of LRDs over a DESI-like (14,000 deg$^2$) footprint delivers a percent-level isotropic distance scale measurement of $D_V/r_d$ across four bins spanning $4\lesssim z\lesssim9$. LRDs are therefore a compelling target for future wide-field near- to mid-infrared spectroscopy aimed at mapping large-scale structure deep into the matter-dominated era.
Source: arXiv (Cornell University)
Authors: Zebrowski, Jessica A., Naidu, Rohan P.
Institutions: University of Hawaiʻi at Mānoa, University of Hawaii System
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, U.S. Department of Energy, Gordon and Betty Moore Foundation, Ministerio de Ciencia e Innovación, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Office of Science, Science and Technology Facilities Council, Division of Astronomical Sciences, High Energy Physics, Fermilab, Lawrence Berkeley National Laboratory
OpenAlex ID: W7212040121