A first look at quasar-galaxy clustering at $z\simeq7.3$

Jan-Torge Schindler, Joseph F. Hennawi, Frederick B. Davies, Sarah E. I. Bosman, Feige Wang, Jinyi Yang, Anna-Christina Eilers, Xiaohui Fan, Koki Kakiichi, Elia Pizzati, Riccardo Nanni

First listed 2025-10-09 | Last updated 2026-03-20

Abstract

We present JWST observations of the environments surrounding two high-redshift quasars, J0252$-$0503 at $z = 7.0$ and J1007$+$2115 at $z = 7.5$, which enable the first constraints on quasar-galaxy clustering at $z \sim 7.3$. Galaxies in the vicinity of the quasars are selected through ground-based and JWST/NIRCam imaging and then spectroscopically confirmed with JWST/NIRSpec using the multi-shutter assembly (MSA). Over both fields, we identified 51 $z>5$ galaxies, of which eight are found within a $Δv_{\textrm{LOS}}=\pm1500 \rm{km} \rm{s}^{-1}$ line-of-sight velocity window from the quasars and another eight in the background. The galaxy J0252\_8713, located just $7\,\rm{pkpc}$ and $Δv_{\textrm{LOS}} \approx 360\,\rm{km}\,\rm{s}^{-1}$ from quasar J0252$-$0503, emerges as a compelling candidate for one of the most distant quasar-galaxy mergers. Combining the galaxy discoveries over the two fields, we measure the quasar-galaxy cross-correlation and obtain a correlation length of $r_0^{\rm{QG}}\approx7.6_{-1.6}^{+1.7}\,h^{-1}\,\rm{cMpc}$, based on a power-law model with a fixed slope of $γ_{\rm{QG}} = 2.0$. Under the assumption that quasars and galaxies trace the same underlying dark matter density fluctuations, we infer a minimum dark matter halo mass for $z\simeq7.3$ quasars of $\log_{10}(M_{\textrm{halo, min}}/\textrm{M}_{\odot})= 11.6_{-0.7}^{+0.6}$ in a halo model framework. Compared to measurements from EIGER at $\langle z \rangle = 6.25$ and ASPIRE at $\langle z \rangle = 6.7$ (where $\log_{10}(M_{\textrm{halo, min}}/\textrm{M}_{\odot}) \gtrsim 12.3$), our clustering results provide tentative evidence for a non-monotonic redshift evolution of quasar clustering properties. We further estimate a quasar duty cycle of $f_{\rm{duty}}\approx0.05\%$, consistent with constraints from quasar proximity zones and IGM damping wings. (abridged)

Short digest

JWST/NIRCam+NIRSpec around two frontier quasars, J0252−0503 (z=7.0) and J1007+2115 (z=7.5), delivers the first quasar–galaxy clustering constraint at z≈7.3. From 51 z>5 galaxies, eight fall within ΔvLOS=±1500 km s−1 of the quasars; notably J0252_8713 sits just 7 pkpc away with Δv≈360 km s−1, a compelling z>7 merger candidate. Combining both fields yields r0^QG≈7.6+1.7−1.6 h−1 cMpc (γ=2), implying log10(Mhalo,min/M⊙)=11.6+0.6−0.7 and a tiny duty cycle f_duty≈0.05%. Relative to EIGER/ASPIRE results at z≈6–6.7 (≳10^12.3 M⊙), this hints at non‑monotonic redshift evolution in quasar clustering, sharpening where the earliest SMBHs live in the dark‑matter hierarchy.

Key figures to inspect

• Figure 1: Inspect the NIRSpec discovery spectra near J1007+2115 for the continuum break and marked emission features to verify redshifts and velocity offsets that enter the cross‑correlation sample.
• Figure 2: Do the same around J0252−0503, paying special attention to the spectrum of J0252_8713 to check the ≈360 km s−1 offset and the robustness of its line/break identification supporting the merger claim.
• Figure 3: Use the NIRCam composites plus separation–redshift panels to see which galaxies fall inside the ±1500 km s−1 window, compare the two fields’ galaxy distributions, and note the serendipitous LRD marked by the black star.
• Figure 4: Examine the close pair around J0252−0503; the 7 pkpc projected separation and morphology of the diffuse companion help assess interaction/merger plausibility at z≈7.