Quasar Radiative Feedback May Suppress Galaxy Growth on Intergalactic Scales at $z = 6.3$

TL;DR

This study demonstrates that the intense radiative output of a luminous quasar at $z=6.3$ can suppress nebular [O III] emission in nearby intergalactic galaxies out to about $\sim$7 $\mathrm{cMpc}$, while leaving the UV-continuum luminosity largely unchanged. By leveraging JWST/NIRCam grism data from the SAPPHIRES and EIGER surveys, the authors quantify the suppression through the ratio $\log_{10}(L_{5008}/L_{1500})$ and model the local quasar radiation field with a attenuation-based photoionization profile $\Gamma_{\rm qso}(r)$, finding a strong, signficant transverse trend and weaker LOS trends. The results imply a recent radiative episode with a cumulative duration of $t_{\rm Q} \sim 3.1$ Myr, favoring rapid $\mathrm{H_2}$ photodissociation over long-term thermal heating as the primary mechanism. Cross-field comparisons with other $z\sim6.3$ quasars suggest the suppression is a real, geometry-dependent effect, with implications for quasar lifetimes, duty cycles, and the census of galaxies around luminous quasars during reionization.

Abstract

We present observational evidence that intense ionizing radiation from a luminous quasar suppresses nebular emission in nearby galaxies on intergalactic scales at $z=6.3$. Using JWST/NIRCam grism spectroscopy from the SAPPHIRES and EIGER programs, we identify a moderate but statistically significant decline in [O\,\textsc{iii}]\,$\lambda5008$ luminosity relative to the UV continuum ($L_{5008}/L_{1500}$) among galaxies within $\sim$ 7 comoving Mpc (cMpc) of the quasar J0100$+$2802, the most UV-luminous quasar known at this epoch ($M_{1450}=-29.26$). While $L_{1500}$ remains roughly constant with transverse distance, $L_{5008}$ increases significantly, suggesting suppression of very recent star formation toward the quasar. The effect persists after controlling for completeness, local density, and UV luminosity, and correlates with the projected photoionization-rate profile $Γ_{\mathrm{qso}}$. A weaker but directionally consistent suppression in $L_{5008}/L_{1500}$ is also observed along the line of sight. The transverse suppression radius ($\sim$ 7 cMpc) implies a recent radiative episode with a cumulative duration $\sim$ 3.1 Myr, shorter than required for thermal photoheating to dominate and thus more naturally explained by rapid H$_2$ photodissociation and related radiative processes. Environmental effects alone appear insufficient to explain the signal. Our results provide direct, geometry-based constraints on large-scale quasar radiative feedback and recent quasar lifetimes.

Figures (6)

• Figure 1: Sky map of the J0100$+$2802 field, combining NIRCam F356W mosaics from SAPPHIRES (top) and EIGER (bottom). Galaxies at $z \approx 6.3$ (near the quasar redshift; red circles), $z \approx 6.2$ (foreground; green hexagon), and $z \approx 6.8$ (background overdensity; orange squares) are shown with symbol sizes scaled by their observed [O iii] $\lambda5008$ luminosities. The black cross marks the quasar position. We also show other galaxies with transverse distance from the quasar $\Delta r < 7$ cMpc on the sky map just for reference. The inset shows the projected distribution along the line of sight, with transverse separation $\Delta r$ plotted against line-of-sight distance $\Delta d$ from the quasar.
• Figure 2: Left: Field-averaged detection completeness for galaxies with $L_{5008} > 10^{42}\,\mathrm{erg\,s^{-1}}$ as a function of projected transverse distance $\Delta r$ (cMpc) from J0100$+$2802, for the SAPPHIRES (blue squares) and EIGER (gray circles) mosaics. The horizontal dashed lines mark 50% and 60% completeness. The vertical dotted line at $\Delta r = 7$ cMpc indicates where both fields reach $\gtrsim 50\%$ completeness (from injection-recovery tests). Right: [O iii]-to-UV luminosity ratio ($\log_{10}(L_{5008}/L_{1500})$) versus $\Delta r$ for galaxies that pass the $\Delta r$-dependent completeness cut ($>50\%$; red points). The solid black line is the best-fit linear trend derived from the unbinned data points, and the shaded band shows the 16th to 84th percentile bootstrap interval from mock downsampling to uniform 60% completeness. Binned averages (five galaxies per bin) are shown as red squares with error bars, which represent 1$\sigma$ uncertainties in the mean within each bin. The dot-dashed purple curve shows the expected quasar photoionization rate, and the right-hand axis gives $\log_{10}(\Gamma_{\rm QSO}/\Gamma_{\rm bg})$.
• Figure 3: Left: Similar to Figure \ref{['fig:trend']}, [O iii]-to-UV ratio $\log_{10}(L_{5008}/L_{1500})$ versus transverse distance $\Delta r$ for galaxies near the quasar redshift ($z \approx 6.3$, red), in the foreground ($z \approx 6.2$, green), and in the background overdensity ($z \approx 6.8$, orange). Only data points with $>50\%$ completeness are shown here. Solid, dotted, and dashed curves show completeness-matched median fits for the three slices, with shaded bands indicating the 16--84% ranges. Binned averages (five galaxies per bin) with bootstrap uncertainties are overplotted. Right: Cumulative distributions (CDFs) of $\log_{10}(L_{5008}/L_{1500})$ for galaxies within $\Delta r < 7$ cMpc of the quasar, comparing $z \approx 6.3$ (red), $z \approx 6.2$ (green), and $z \approx 6.8$ (orange). The background sample shows higher ratios than the $z \approx 6.3$ sample (K--S $p=0.017$), while the foreground is more similar ($p=0.167$), consistent with the visual impression from the left panel.
• Figure 4: Left: [O iii]-to-UV luminosity ratio ($\log_{10}(L_{5008}/L_{1500})$) versus local overdensity, estimated with a $k=5$ nearest-neighbor metric in 3D over the full sample of 130 emitters ($5.3<z<6.9$) and normalized to the field average. The combined control sample (foreground $z\approx6.2$ plus background $z\approx6.8$; blue hexagons) shows a weak positive trend ($\rho=0.18$, $p=0.255$), while the $z\approx6.3$ near-QSO sample (red circles) shows a negative trend ($\rho=-0.63$, $p=0.002$). The full sample shows no significant correlation ($\rho=-0.05$, $p=0.600$). These patterns indicate that the quasar-distance dependence is unlikely to be driven by local overdensity alone. Right: Rest-frame UV luminosity ($\log_{10} L_{1500}$) as a function of transverse distance $\Delta r$ from J0100$+$2802. Both the near-$z_{\rm QSO}$ and control samples show no significant trend with distance, with a typical scatter of about 0.2 dex. The y-axis span (in dex) matches Figure \ref{['fig:trend']} (right) for visual comparison.
• Figure 5: Left: Predicted quasar photoionization rate $\Gamma_{\rm QSO}$ relative to the metagalactic UV background $\Gamma_{\rm bg}$ as a function of comoving distance $r$ for four luminous quasars in the EIGER fields at $z \approx 6.3$. J0100$+$2802 (solid purple) exhibits the strongest radiative impact. The horizontal dashed and dotted lines indicate $\Gamma_{\rm QSO}/\Gamma_{\rm bg}=1$ and $10^3$. Right: [O iii]-to-UV luminosity ratio $\log_{10}(L_{5008}/L_{1500})$ versus $\log_{10}\Gamma_{\rm QSO}(r)$ for galaxies near J0100$+$2802 (red circles) and J1148$+$5251 (blue pentagons). Distances for J1148 sources are rescaled to match the J0100 photoionization profile; the top axis shows the corresponding scaled transverse separation $\Delta r'$ (cMpc). The black curve and shaded band show the best-fit relation and 68% interval from the J0100 field in Figure \ref{['fig:trend']} (right), re-plotted as a function of $\Gamma_{\rm QSO}(r)$. The J1148 data show a qualitatively similar but weaker trend, with larger scatter likely due to smaller sample size and lower quasar luminosity. Despite this, the J1148 binned trend (cyan hexagons) is broadly consistent with the J0100 binned points (orange squares). The other EIGER quasars (J1030$+$0524, J159$-$02) lack sufficient [O iii] emitters at small radii to assess this effect.