Galaxy cluster temperature maps from joint X-ray and SZ maps with The Three Hundred hydrodynamical simulations

TL;DR

This work validates a method to map the intra-cluster medium temperature in 2D by combining X-ray–derived density information with SZ pressure, using the Three Hundred hydrodynamical simulations as a testbed. The key challenge is the effective length l_eff that links projected density and pressure, for which the authors develop Generalized High Pass (GHP) templates calibrated on simulated clusters. They show that T_SZX can reproduce theoretical temperatures such as the mass-weighted T_mw and spectroscopic-like T_sl within about 10% bias and similar scatter, with the GHP approach outperforming traditional density-profile-based models. The findings support applying this method to real high-resolution SZ data (e.g., NIKA2 LPSZ) while carefully accounting for resolution and low-mass system limitations; a follow-up paper applies the method to realistic mocks and observations, including instrumental effects.

Abstract

Galaxy clusters can be used as powerful cosmological probes, provided one can obtain accurate mass estimates, which requires a precise knowledge of the underlying astrophysics of galaxy clusters. For these purposes, spatially resolved measurements of the thermodynamic properties of intra-cluster medium (ICM), such as density and temperature, are necessary. In particular, temperature estimates are traditionally obtained through spatially resolved X-ray spectroscopy. Such measurements suffer from their sensitivity to the chosen energy calibration, may exhibit inherent biases, and are especially hard to perform at high redshift as they require deep observations. In recent years however, millimetre wavelength data with high spatial resolution, comparable to the one of current X-ray telescopes, have begun to be available. This has enabled the implementation of new methods to infer and map the cluster temperature in individual clusters, using the combination of density maps from X-ray data and pressure maps from millimetre data. In this paper, we present the first systematic validation of this approach on a large sample of synthetic clusters generated in The Three Hundred hydrodynamical simulations. We show that we are able to recover theoretical estimates of the temperature, namely the mass-weighted and spectroscopic-like temperatures, within biases of the order of $\lesssim 1\%$ in the best cases, up to $\sim 10\%$ in average, with scatters of the order of $10\%$. To prepare the application of this approach to observed data, we discuss the modelling of the effective length $l_\mathrm{eff}$, a key quantity necessary for the combination of X-ray and SZ projected data. In particular we provide templates calibrated on simulations for this quantity, and investigate their impact in the recovery of the temperature map, compared to other standard models.

Figures (12)

• Figure 1: Left: Effective length map for the main cluster of region 211 of the snapshot 101, at $z =$0.817. The two rings correspond to $\mathrm{R}_{500}$ and $\mathrm{R}_{200}$. Right : 1D profiles of the effective length for all clusters in our sample. We give in addition the median $l_{\mathrm{eff}}$ profiles computed for the full sample (green), the most relaxed (blue) and the most disturbed (red) clusters of the sample. The vertical dashed lines correspond to the $1.0 \mathrm{R}_{500}$ and $1.4 \mathrm{R}_{500} \sim \mathrm{R}_{200}$.
• Figure 2: Two examples of comparison between $\mathrm{T_{SZX}}$ derived using the true $l_{\mathrm{eff}}$ and $\mathrm{T_{SZX}}$ obtained using a modelled effective length. The two rings correspond to $\mathrm{R}_{500}$ and $\mathrm{R}_{200}$. The color scale of the comparative maps ranges from -50% to +50%. The levels of the contours inside $\mathrm{R}_{500}$ range from -10% to +10%. For each of the two clusters, the final panel shows the $\mathrm{T_{SZX}}$ map obtained using the optimal (Relaxed, Disturbed or Median) GHP template. Top two rows: Main cluster of the region 75 of the snapshot 110, at $z =$0.490. Bottom two rows: Main cluster of the region 135 of the snapshot 107, at $z =$0.592.
• Figure 3: Median bias and scatter between $\mathrm{T_{SZX,true}}$ and $\mathrm{T_{SZX,template}}$, for all the clusters in the sample, depending on z (left column), $\mathrm{M_{500}}$ (middle column) and $\left<T_{mw}\right>_{R_{500}}$ (right column). Top row: Biases and scatters taken at $\mathrm{R}_{500}$. Bottom row: Biases and scatters taken at $\mathrm{R}_{200}$.
• Figure 4: $\mathrm{T_{SZX}}$ maps obtained for all the clusters in our sample, using the optimal GHP template (Relaxed, Disturbed or Median) for each cluster.
• Figure 5: Comparison between $\mathrm{T_{SZX}}$, obtained using different models, and $\mathrm{T_{mw}}$ for all the clusters in our sample, depending on their redshift, mass, and mean temperature at $\mathrm{R}_{500}$. Top row : Biases and scatters measured at $\mathrm{R}_{500}$. Bottom row : Biases and scatters measured at $\mathrm{R}_{200}$.