[論文レビュー] Identification of low redshift groups and clusters of galaxies in the X-CLASS survey and the X-ray luminosity-temperature relation

Q. Moysan, F. Sarron+17 more|arXiv (Cornell University)|Mar 24, 2026

Galaxies: Formation, Evolution, Phenomena被引用数 0

ひとこと要約

The paper builds a spectroscopically complete sample of 155 low-redshift (0.07<z<0.2) X-ray selected groups and clusters from X-CLASS, and derives the Lx–T scaling relation for these low-mass systems using Bayesian modelling and careful redshift and gas property measurements.

ABSTRACT

Properties of the hot intracluster and intragroup medium are mostly set by the underlying gravitational potential well, although complex astrophysical processes at play during their buildup may leave a significant imprint. Observational constraints on the degree and scales of such non-gravitational processes require well-selected samples of objects and deep observations of their gas content. We aim to study the scaling relation between two global properties of the hot gas, namely its soft-band X-ray luminosity ($L_X$) and its temperature ($T$), by studying a sample of low-mass systems associated with precise redshifts, simultaneously accounting for sample selection biases and associated measurement uncertainties. This work takes as input a large catalogue of X-ray-selected galaxy clusters (X-CLASS). We perform a thorough revision of the redshifts of sources using deep photometric data from the Legacy Surveys and our own tailored spectroscopic follow-up of 52 low-redshift systems. We devise a spectroscopically complete sample of 155 low-redshift ($0.07

研究の動機と目的

• Improve redshift completeness and accuracy for X-CLASS clusters using photometric and spectroscopic data.
• Construct a spectroscopically complete sample of low-redshift systems (0.07<z<0.2) with measured X-ray gas properties.
• Measure X-ray gas temperature, metallicity, and luminosity to model the Lx–T scaling relation.
• Assess how non-gravitational processes affect Lx–T in the group regime compared to massive clusters.

提案手法

• Revise X-CLASS redshifts with deep Legacy Surveys photometry and targeted spectroscopy (MISTRAL) to obtain 155 low-z systems (0.07<z<0.2).
• Compute cluster redshifts by combining photometric redshifts from photXclus and RedMaPPer, with decision rules by z_phot thresholds.
• Measure T500 and Z500 from XMM-Newton spectra using XSPEC, with R500 determined iteratively from T500–R500 scaling relations.
• De-project X-ray surface brightness with MBProj2D to derive Lx within R500 and account for PSF and background.
• Model Lx–T in a Bayesian framework, accounting for selection effects and measurement uncertainties.

Figure 1: Performances of the photometric redshift estimates. Top : photometric redshifts vs. spectroscopic redshifts for confirmed X-CLASS clusters. Bottom : Bias (red) and NMAD scatter (blue) of the photometric redshift estimates as a function of spectroscopic redshifts for confirmed X-CLASS clust

実験結果

リサーチクエスチョン

• RQ1 What is the Lx–T scaling relation for low-mass galaxy groups and clusters (0.07<z<0.2) in the X-CLASS sample?
• RQ2 How do updated photometric and spectroscopic redshifts affect the completeness and reliability of the X-CLASS low-redshift sample?
• RQ3 Is the Lx–T relation steeper for low-mass systems relative to self-similar expectations, and what does this imply for non-gravitational physics?
• RQ4 What is the distribution of gas properties (T500, Z500, LX) in the X-CLASS-LR sample and their inferred masses (M500,est)?

主な発見

• The X-CLASS-LR sample comprises 155 clusters/groups with median T500 = 1.7 keV and median LX = 10^43 erg s^-1.
• The inferred Lx–T relation slope is B = 3.2 ± 0.1, steeper than the self-similar prediction.
• About 57% of the sample has T500 < 2 keV, indicating a predominance of low-mass systems; median M500,est ≈ 6×10^13 M⊙.
• The Lx–T relation supports a scenario where luminosity declines more rapidly with decreasing mass in the group regime, likely due to efficient gas expulsion by feedback in shallow potentials.
• Redshift upgrades and updated redshift flags (ZSP) increased spectroscopic confirmation in X-CLASS, yielding a large, homogeneous low-z sample for scaling analyses.
• The cluster photometric redshift approach photXclus (low-z favored) and RedMaPPer (higher-z favored) provide a robust combined z_phot with NMAD ~ 0.0044(1+z).

Figure 2: Spectra of two galaxies (G2 and G3) in xclass1365 as observed with MISTRAL. The redshift measurements are based on the main absorption lines detected and identified using the template spectrum of an early-type galaxy (in orange, redshifted to $z=0.1554$ for G2 and $z=0.1593$ for G3 as meas