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

TL;DR

This study leverages JWST imaging and spectroscopy to constrain the quasar-galaxy clustering environment at $z\simeq7.3$ by examining galaxies around two luminous quasars at $z\approx7.0$–$7.5$. Using a cross-correlation framework and a carefully modeled selection function, the authors find an average overdensity around the quasars and derive a cross-correlation length of $r_0^{QG}\approx7.60_{-1.61}^{+1.65}\,h^{-1}\,\mathrm{cMpc}$ with a fixed slope $\gamma_{QG}=2.0$. Under a halo-model assumption and a galaxy auto-correlation length of $r_0^{GG}\approx5\,h^{-1}\mathrm{cMpc}$, they infer a minimum host halo mass of $\log_{10}(M_{halo,min}/M_{\odot})=11.64_{-0.64}^{+0.56}$ and a quasar duty cycle of $\log_{10}(f_{duty})=-3.34_{-1.90}^{+2.35}$, corresponding to a characteristic quasar lifetime $\log_{10}(t_{QSO}/\mathrm{yr})\approx5.52_{-1.90}^{+2.35}$. These results suggest a possible non-monotonic evolution of quasar clustering at $z\gtrsim6$ and, when interpreted with complementary constraints, imply short UV-luminous quasar phases at this epoch. However, the conclusions are limited by small-number statistics and cosmic variance, highlighting the need for larger samples and uniform tracers in future work.

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 identify 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 $\log_{10}(M_{\textrm{halo, min}}/\textrm{M}_{\odot})= 11.6\pm0.6$ 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 $f_{\rm{duty}}\approx0.1\%$, consistent with constraints from quasar proximity zones and IGM damping wings. (abridged)

Figures (9)

• Figure 1: Discovery spectra of galaxies within $\|\Delta v_{\textrm{LOS}}\|=1500\,\rm{km}\,\rm{s}^{-1}$ to the quasar J1007$+$2115 ($z=7.5149$). The spectrum is shown in black with vertical orange annotations highlighting possible emission line features as well as the position of the $\text{Ly}\alpha$ break. Uncertainties ($1\sigma$) on the spectral flux are shown in grey.
• Figure 2: Discovery spectra of galaxies within $\|\Delta v_{\textrm{LOS}}\|=1500\,\rm{km}\,\rm{s}^{-1}$ to the quasar J0252$-$0503 ($z=7.00$). The spectrum is shown in black with vertical orange annotations highlighting possible emission line features as well as the position of the $\text{Ly}\alpha$ break. Uncertainties ($1\sigma$) on the spectral flux are shown in grey.
• Figure 3: Top panels: JWST NIRCam composite image (R: F444W, G: F277W, B: F115W) of the J1007$+$2115 (left) and J0252$-$0503 (right) quasar fields. The quasar position is indicated by the tip of the white arrow. The positions of galaxies within a line-of-sight velocity window of $\|\Delta v_{\textrm{LOS}}\|=1500\,\rm{km}\,\rm{s}^{-1}$ are indicated by white circles. Bottom panels: Angular separation of galaxies relative to quasar J1007$+$2115 (left) and J0252$-$0503 (right) as a function of their redshift. Galaxies are marked with filled circles, colored according to their line-of-sight velocity. Grey solid lines in the background depict the respective quasar spectra with the quasar redshift marked by the dotted grey line. The line-of-sight velocity window for clustering is highlighted by the grey region. The black star in the bottom left panel marks the position of a serendipitously discovered $z\approx7.3$ LRD Schindler2025.
• Figure 4: JWST NIRCam composite cutout ($7" \times7"$; R: F444W, G: F277W, B: F115W) of the quasar J0252$-$0503 and its immediate environment. The quasar is the bright point source near the center. We highlight the companion galaxy, a diffuse source to the top right of the quasar, with a white circular border. The distance to the companion is $1\farcs26$, equivalent to $6.58\,\rm{pkpc}$ or $36.87\,\rm{ckpc}\,\rm{h}^{-1}$ at $z=7$.
• Figure 5: The background shows the F277W mosaic image of the J0252$-$0503 quasar field. We overplot the two MSA pointings in blue. The quasar position is depicted as an orange dot and we highlight the radial boundaries of the four annuli with solid orange lines. This image underlines that within some annuli there are gaps not covered by the NIRSpec MSA pointing and/or the NIRCam imaging that are accounted for in our coverage selection function $S_R(R)$.