XMM-Newton observations of ten high-redshift CAMIRA clusters of galaxies

TL;DR

This study analyzes deep XMM-Newton observations of ten high-redshift CAMIRA clusters ($0.81 < z < 1.17$) to probe the dynamical state and thermodynamic evolution of the ICM at early times. By combining X-ray measurements of temperature and bolometric luminosity with weak-lensing masses and CAMIRA richness, the authors derive $N$–$T$, $L$–$T$, $N$–$M$, and $L$–$M$ scaling relations across $0.14 < z < 1.17$, finding no strong evidence for redshift evolution beyond self-similar expectations. They quantify cluster dynamical states via BCG–X-ray peak offsets, finding only ~10% of high-$z$ clusters dynamically relaxed, consistent with a picture of predominantly disturbed morphologies during rapid assembly. Additionally, AGN activity among member galaxies is significantly higher at high redshift, especially in cluster outskirts, suggesting enhanced AGN triggering during early assembly and potential links to the ICM state; these results provide important context for interpreting upcoming eROSITA results. Together, the findings indicate that massive clusters at $z \sim 1$ already follow mature scaling relations while exhibiting dynamic youth, offering valuable benchmarks for cluster physics and cosmology in the era of wide-area X-ray surveys.

Abstract

We present results from XMM-Newton observations of ten high-redshift ($0.81 < z < 1.17$) galaxy clusters selected from the CAMIRA catalog based on high richness ($N > 40$). These massive clusters, identified in the Hyper Suprime-Cam Subaru Strategic Program field, provide an ideal sample for probing the dynamical state of the intracluster medium (ICM) in the early Universe. We performed uniform X-ray imaging and spectral analyses to measure the ICM temperature and bolometric luminosity, and investigated cluster morphology through offsets between the brightest cluster galaxy (BCG) and the X-ray peak. Extended X-ray emission was detected from all targets, but only one system was classified as dynamically relaxed, indicating a low relaxed fraction ($\sim 10\%$) at high redshift. By combining this high-$z$ sample with a lower-redshift CAMIRA cluster sample, we derived scaling relations among richness, temperature, luminosity, and mass. The results are broadly consistent with predictions from both the self-similar model and the baseline model incorporating the mass--concentration relation. We find no significant redshift evolution, strengthening the view that cluster scaling relations are largely established by $z \sim 1$. We also examined the AGN fraction among member galaxies and found significantly higher AGN activity in high-redshift clusters, particularly in the outskirts, suggesting enhanced AGN triggering during early cluster assembly and a possible connection to the thermodynamic state of dynamically young clusters. These findings provide new insights into the formation and evolution of massive clusters and the thermodynamic history of the ICM, and complement large-area X-ray surveys such as eROSITA.

Figures (5)

• Figure 1: Left: Mass versus redshift for the optically-selected clusters (Top; Oguri18), X-ray-selected clusters (middle, eRASS1; Bulbul24), and SZ-selected clusters (bottom, ACT; 2021ApJS..253....3H). The background colors represent $\log_{10}\left(dN/(dVdM)\,h_{70}^4{\rm Gpc}^{-3}(10^{14}M_\odot)^{-1}\right)$. The red solid boxes correspond to the selection function of the present sample. The blue open and filled circles denote the masses inferred by cluster richness and WL mass, respectively. Right: Number density of clusters per a co-moving volume of 1 $h^{-3}{\rm Mpc}^3$, where the mass uncertainties are not taken into account. The hatched region indicates the redshift range covered by the cluster sample analyzed in this work. Alt text: Two-panel figure. The left panel shows three scatter plots of cluster mass versus redshift for optically selected, X ray selected, and Sunyaev Zeldovich selected samples, overlaid on a color coded density map. Red boxes mark the selection region of the present sample, and circles indicate richness based and weak lensing based mass estimates. The right panel shows a line graph of cluster number density as a function of mass and redshift.
• Figure 2: HSC I-band images of the high-redshift CAMIRA clusters (color) with superposed contours of X-ray intensities (white) and galaxy density maps (red). In each panel, the X-ray centroid, X-ray peak, and BCG positions are marked with a magenta "x", cyan "+", and green "+", respectively. Alt text: Multi panel figure showing optical images of galaxy clusters with overlaid maps. Each panel displays an I band image with contours indicating X ray surface brightness and contours indicating galaxy density.
• Figure 3: Histograms of BCG-X-ray centroid offset and BCG-X-ray peak offset in units of kpc and $R_{500}$. The filled and open histograms show the distributions of 10 high-redshift clusters (this work) and 17 low-redshift clusters Ota20, respectively. The vertical dotted line and dashed line indicate the median of two samples. Alt text: Multiple histograms comparing distributions of brightest cluster galaxy offsets from the X ray centroid and from the X ray peak. Each histogram is presented both in kiloparsec units and normalized by the cluster radius R five hundred.
• Figure 4: Scaling relations of the CAMIRA clusters. The upper two panels show the richness--temperature ($N$--$T$) and luminosity--temperature ($L$--$T$) relations, while the lower two panels show the richness--mass ($N$--$M$) and luminosity--mass ($L$--$M$) relations. Each data point is color-coded according to the redshift of the cluster, as indicated by the color bar. For comparison, high-richness CAMIRA clusters observed in the eFEDS field Ota23 are shown in gray. The solid lines represent the best-fit scaling relations, calculated for the reference redshift $z=0.79$. Alt text: Multi panel scatter plots showing scaling relations for the CAMIRA clusters. Each panel displays data points plotted against fitted trend lines. The points include two samples: CAMIRA clusters in the present study and comparison clusters from the eFEDS field shown as separate markers.
• Figure 5: (a) Cluster-averaged AGN power fraction ($f^{\mathrm{cl}}_{\mathrm{AGN}}$) as a function of redshift for the sample of 23 galaxy clusters cross-matched with the CAMIRA s21a catalog Toba24. Blue and red symbols correspond to low-redshift ($z_{\mathrm{cl}} < 0.8$) and high-redshift ($z_{\mathrm{cl}} > 0.8$) clusters, respectively. (b) Radial profile of the AGN power fraction ($f^{\mathrm{mem}}_{\mathrm{AGN}}$) of member galaxies as a function of normalized cluster-centric radius ($R/R_{200}$). The blue and red crosses represent the average profiles for low-$z$ and high-$z$ clusters, respectively. Alt text: Two panel figure showing active galactic nucleus power fractions in galaxy clusters. Panel a displays a scatter plot of cluster averaged power fraction as a function of redshift for two groups of clusters, low redshift and high redshift, plotted with different symbol types. Panel b shows the radial profile of the member galaxy power fraction as a function of the normalized cluster centric radius, again with two symbol sets representing the two redshift groups.