arXiv subjects

Hervé Bourdin

Publications and source records attributed to Hervé Bourdin.

14 recordsLinked to original sources

arXiv2026

CHEX-MATE: X-ray surface brightness discontinuities across a representative cluster sample

We analyze the presence of X-ray surface brightness (SB) discontinuities, such as shocks and cold fronts, in the intracluster medium (ICM) of the 116 galaxy clusters from the CHEX-MATE sample. These features arise from accretion-related processes, including the merging of subclumps onto the main cluster halo and the sloshing of cold gas in a higher-entropy environment. We identify these structures in the XMM CHEX-MATE maps by examining both the SB residuals, obtained by subtracting a cluster model from the observations, and the gradient variations across X-ray images. We validate our method with an extensive analysis and comparison of the discontinuities described already in the literature. Our analysis reveals 66 discontinuities, 32 of which are newly detected, in 48 objects ($\sim$41%). We find that discontinuities in relaxed systems tend to be closer to the core, weaker, and less aligned with the global X-ray morphology compared to those in disturbed systems. Using wavelet-based temperature maps, we provide a preliminary classification of these discontinuities, proposing the occurrence of 8 putative shocks and 34 cold fronts. Furthermore, about 48% of the systems with extended radio emission show evidence of ICM discontinuities; conversely, $\sim$88% of the objects with detected discontinuities have an associated diffuse radio emission. This work also explores the limitations of using XMM data, characterized by relatively low spatial resolution, for detecting and analyzing such features, highlighting the challenges and potential biases introduced by instrumental constraints.

astro-ph.CO↗

arXiv2024

CHEX-MATE : turbulence in the ICM from X-ray surface brightness fluctuations

The intra-cluster medium is prone to turbulent motion that will contribute to the non-thermal heating of the gas, complicating the use of galaxy clusters as cosmological probes. Indirect approaches can estimate the intensity and structure of turbulent motions by studying the associated fluctuations in gas density and X-ray surface brightness. In this work, we want to constrain the gas density fluctuations at work in the CHEX-MATE sample to obtain a detailed view of their properties in a large population of clusters. We use a simulation-based approach to constrain the parameters of the power spectrum of density fluctuations, assuming a Kolmogorov-like spectrum and including the sample variance, further providing an approximate likelihood for each cluster. This method requires clusters to be not too disturbed, as fluctuations can originate from dynamic processes such as merging. Accordingly, we remove the less relaxed clusters (centroid shift $w>0.02$) from our sample, resulting in a sample of 64 clusters. We define different subsets of CHEX-MATE to determine properties of density fluctuations as a function of dynamical state, mass and redshift, and investigate the correlation with the presence or not of a radio halo. We found a positive correlation between the dynamical state and density fluctuation variance, a non-trivial behaviour with mass and no specific trend with redshift or the presence/absence of a radio halo. The injection scale is mostly constrained by the core region. The slope in the inertial range is consistent with Kolmogorov theory. When interpreted as originating from turbulent motion, the density fluctuations in $R_{500}$ yield an average Mach number of $M_{3D}\simeq 0.4\pm 0.2$, an associated non-thermal pressure support of $ P_{turb}/P_{tot}\simeq (9\pm 6) \%$ or a hydrostatic mass bias $b_{turb}\simeq 0.09\pm 0.06$, in line with what is expected from the literature.

astro-ph.CO↗

arXiv2024

Resolving high-z Galaxy Cluster properties through joint X-ray and Millimeter analysis: a case study of SPT-CLJ0615-5746

We present a joint millimetric and X-ray analysis of hot gas properties in the distant galaxy cluster SPT-CLJ0615-5746 ($z = 0.972$). Combining Chandra observations with the South Pole Telescope (SPT) and Planck data, we perform radial measurements of thermodynamical quantities up to a characteristic radius of $1.2\, R_{500}$. We exploit the high angular resolution of Chandra and SPT to map the innermost region of the cluster and the high sensitivity to the larger angular scales of Planck to constrain the outskirts and improve the estimation of the cosmic microwave background and the galactic thermal dust emissions. Besides maximizing the accuracy of radial temperature measurements, our joint analysis allows us to test the consistency between X-ray and millimetric derivations of thermodynamic quantities via the introduction of a normalization parameter ($η_T$) between X-ray and millimetric temperature profiles. This approach reveals a substantial high value of the normalization parameter, $η_T=1.46^{+0.15}_{-0.22}$, suggesting that the gas halo is aspherical. Assuming hot gas hydrostatic equilibrium within complementary angular sectors that intercept the major and minor elongation of the X-ray image, we infer a halo mass profile that results from an effective compensation of azimuthal variations of gas densities by variations of the $η_T$ parameter. Consistent with earlier integrated X-ray and millimetric measurements, we infer a cluster mass of $M^{\text{HE}}_{500} = 10.67^{+0.62}_{-0.50}\,\, 10^{14}\,M_{\odot}$.

astro-ph.GA↗

arXiv2022

CHEX-MATE: pressure profiles of 6 galaxy clusters as seen by SPT and Planck

Pressure profiles are sensitive probes of the thermodynamic conditions and the internal structure of galaxy clusters. The intra-cluster gas resides in hydrostatic equilibrium within the Dark Matter gravitational potential. However, this equilibrium may be perturbed, e.g. as a consequence of thermal energy losses, feedback and non-thermal pressure supports. Accurate measures of the gas pressure over the cosmic times are crucial to constrain the cluster evolution as well as the contribution of astrophysical processes. In this work we presented a novel algorithm to derive the pressure profiles of galaxy clusters from the Sunyaev-Zeldovich (SZ) signal measured on a combination of Planck and South Pole Telescope (SPT) observations. The synergy of the two instruments made it possible to track the profiles on a wide range of spatial scales. We exploited the sensitivity to the larger scales of the Planck High-Frequency Instrument to observe the faint peripheries, and the higher spatial resolution of SPT to solve the innermost regions. We developed a two-step pipeline to take advantage of the specifications of each instrument. We first performed a component separation on the two data-sets separately to remove the background (CMB) and foreground (galactic emission) contaminants. Then we jointly fitted a parametric pressure profile model on a combination of Planck and SPT data. We validated our technique on a sample of 6 CHEX-MATE clusters detected by SPT. We compare the results of the SZ analysis with profiles derived from X-ray observations with XMM-Newton. We find an excellent agreement between these two independent probes of the gas pressure structure.

astro-ph.CO↗

arXiv2021

Cosmology with the SZ spectrum: measuring the Universe's temperature with galaxy clusters

The hot gas in clusters of galaxies creates a distinctive spectral distortion in the cosmic microwave background (CMB) via the Sunyaev-Zel'dovich (SZ) effect. The spectral signature of the SZ can be used to measure the CMB temperature at cluster redshift ($T_{\rm CMB}(z)$) and to constrain the monopole of the y-type spectral distortion of the CMB spectrum. In this work, we start showing the measurements of $T_{\rm CMB}(z)$ for a sample extracted from the Second Catalog of galaxy clusters produced by Planck (PSZ2) and containing 75 clusters selected from CHEX-MATE. Then we show the forecasts for future CMB experiments about the constraints on the monopole of the y-type spectral distortion of the CMB spectrum via the spectrum of the SZE.

astro-ph.CO↗

arXiv2021

Pressure profiles of distant Galaxy clusters with Planck-SPT data

We present a full set of numerical tools to extract Galaxy Cluster pressure profiles from the joint analysis of Planck and South Pole Telescope (SPT) observations. Pressure profiles are powerful tracers of the thermodynamic properties and the internal structure of the clusters. Tracing the pressure over the cosmic times allows to constraints the evolution of the cluster structure and the contribution of astrophysical phenomena. SPT and Planck are complementary to constrain the cluster structure at various spatial scales. The SPT cluster catalogue counts 677 cluster candidates up to redshift 1.7, it is a nearly mass limited sample, an ideal benchmark to test cluster evolution. We developed a pipeline to first separate the cluster signal from the background and foreground components and then jointly fit a parametric profile model on a combination of Planck and SPT data. We validate our algorithm on a sub-sample of six clusters, common to the SPT and the CHEX-MATE catalogues, comparing the results with the profiles obtained from X-ray observations with XMM-Newton.

astro-ph.CO↗

arXiv2019

Spectral imaging of X-COP galaxy clusters with the Sunyaev-Zel'dovich effect

The Sunyaev-Zel'dovich effect is the ideal probe for investigating the outskirts of galaxy clusters. To map this signal, we apply a spectral imaging technique which combines parametric component separation and sparse representations. Our procedure is an improved version of an existing algorithm, which now features a better treatment of astrophysical contaminants, and the implementation of a new beam deconvolution. We use the most recent frequency maps delivered by \textsl{Planck}, and we consider the clusters analysed in the \textsl{XMM} Cluster Outskirts Project (X-COP). In particular, we focus on the images of two clusters which may be possibly interacting with neighbouring objects, namely A2029 and RXCJ1825. We also highlight the advantages of the new beam deconvolution method, through a comparison with the original version of the imaging algorithm.

astro-ph.CO↗

arXiv2019

Spectral imaging of the thermal Sunyaev-Zel'dovich effect in X-COP galaxy clusters: method and validation

The imaging of galaxy clusters through the Sunyaev--Zel'dovich effect is a valuable tool to probe the thermal pressure of the intra-cluster gas, especially in the outermost regions where X-ray observations suffer from photon statistics. For the first time, we produce maps of the Comptonization parameter by applying a locally parametric algorithm for sparse component separation to the latest frequency maps released by Planck. The algorithm takes into account properties of real cluster data through the two-component modelling of the spectral energy density of thermal dust, and the masking of bright point sources. Its robustness has been improved in the low signal-to-noise regime, thanks to the implementation of a deconvolution of Planck beams in the chi-square minimisation of each wavelet coefficient. We applied this procedure to twelve low-redshift galaxy clusters detected by Planck with the highest signal-to-noise ratio, considered in the XMM Cluster Oustkirts Project (X-COP). Our images show the presence of anisotropic features, such as small-scale blobs and filamentary substructures that are located in the outskirts of a number of clusters in the sample. The significance of their detection is established via a bootstrap-based procedure we propose here for the first time. In particular, we present a qualitative comparison with X-ray data for two interesting systems, namely A2029 and RXCJ1825. Our results are in agreement with the features detected in the outskirts of the clusters in the two bands.

astro-ph.CO↗

arXiv2019

Deriving the Hubble constant using Planck and XMM-Newton observations of galaxy clusters

The possibility of determining the value of the Hubble constant using observations of galaxy clusters in X-ray and microwave wavelengths through the Sunyaev Zeldovich (SZ) effect has long been known. Previous measurements have been plagued by relatively large errors in the observational data and severe biases induced, for example, by cluster triaxiality and clumpiness. The advent of \textit{Planck} allows us to map the Compton parameter y, that is, the amplitude of the SZ effect, with unprecedented accuracy at intermediate cluster-centric radii, which in turn allows performing a detailed spatially resolved comparison with X-ray measurements. Given such higher quality observational data, we developed a Bayesian approach that combines informed priors on the physics of the intracluster medium obtained from hydrodynamical simulations of massive clusters with measurement uncertainties. We apply our method to a sample of 61 galaxy clusters with redshifts up to z < 0.5 observed with Planck and XMM-Newton observations and find H_0=67 \pm 3 km s^{-1} Mpc^{-1}.

astro-ph.CO↗

arXiv2019

LoCuSS: Scaling relations between galaxy cluster mass, gas, and stellar content

We present a simultaneous analysis of galaxy cluster scaling relations between weak-lensing mass and multiple cluster observables, across a wide range of wavelengths, that probe both gas and stellar content. Our new hierarchical Bayesian model simultaneously considers the selection variable alongside all other observables in order to explicitly model intrinsic property covariance and account for selection effects. We apply this method to a sample of 41 clusters at $0.15<z<0.30$, with a well-defined selection criteria based on RASS X-ray luminosity, and observations from Chandra / XMM, SZA, Planck, UKIRT, SDSS and Subaru. These clusters have well-constrained weak-lensing mass measurements based on Subaru / Suprime-Cam observations, which serve as the reference masses in our model. We present 30 scaling relation parameters for 10 properties. All relations probing the intracluster gas are slightly shallower than self-similar predictions, in moderate tension with prior measurements, and the stellar fraction decreases with mass. K-band luminosity has the lowest intrinsic scatter with a 95th percentile of 0.16, while the lowest scatter gas probe is gas mass with a fractional intrinsic scatter of $0.16 \pm 0.03$. We find no distinction between the core-excised X-ray or high-resolution Sunyaev-Zel'dovich relations of clusters of different central entropy, but find with modest significance that higher entropy clusters have higher stellar fractions than their lower entropy counterparts. We also report posterior mass estimates from our likelihood model.

astro-ph.CO↗

arXiv2014

Mapping the particle acceleration in the cool core of the galaxy cluster RX J1720.1+2638

We present new deep, high-resolution radio images of the diffuse minihalo in the cool core of the galaxy cluster RX J1720.1+2638. The images have been obtained with the Giant Metrewave Radio Telescope at 317, 617 and 1280 MHz and with the Very Large Array at 1.5, 4.9 and 8.4 GHz, with angular resolutions ranging from 1" to 10". This represents the best radio spectral and imaging dataset for any minihalo. Most of the radio flux of the minihalo arises from a bright central component with a maximum radius of ~80 kpc. A fainter tail of emission extends out from the central component to form a spiral-shaped structure with a length of ~230 kpc, seen at frequencies 1.5 GHz and below. We find indication of a possible steepening of the total radio spectrum of the minihalo at high frequencies. Furthermore, a spectral index image shows that the spectrum of the diffuse emission steepens with the increasing distance along the tail. A striking spatial correlation is observed between the minihalo emission and two cold fronts visible in the Chandra X-ray image of this cool core. These cold fronts confine the minihalo, as also seen in numerical simulations of minihalo formation by sloshing-induced turbulence. All these observations favor the hypothesis that the radio emitting electrons in cluster cool cores are produced by turbulent reacceleration.

astro-ph.CO↗

arXiv2014

LoCuSS: Hydrostatic Mass Measurements of the High-$L_X$ Cluster Sample -- Cross-calibration of Chandra and XMM-Newton

We present a consistent analysis of Chandra and XMM-Newton observations of an approximately mass-selected sample of 50 galaxy clusters at $0.15<z<0.3$ -- the "LoCuSS High-$L_X$ Sample". We apply the same analysis methods to data from both satellites, including newly developed analytic background models that predict the spatial variation of the Chandra and XMM-Newton backgrounds to $<2\%$ and $<5\%$ precision respectively. To verify the cross-calibration of Chandra and XMM-Newton-based cluster mass measurements, we derive the mass profiles of the 21 clusters that have been observed with both satellites, extracting surface brightness and temperature profiles from identical regions of the respective datasets. We obtain consistent results for the gas and total hydrostatic cluster masses: the average ratio of Chandra- to XMM-Newton-based measurements of $M_{\rm gas}$ and $M_X$ at $r_{500}$ are $0.99\pm0.02$ and $1.02\pm0.05$, respectively with an intrinsic scatter of $\sim3\%$ for gas masses and $\sim8\%$ for hydrostatic masses. Comparison of our hydrostatic mass measurements at $r_{500}$ with the latest LoCuSS weak-lensing results indicate that the data are consistent with non-thermal pressure support at this radius of $\sim7\%$. We also investigate the scaling relation between our hydrostatic cluster masses and published integrated Compton parameter $Y_{sph}$ measurements from the Sunyaev-Zel'dovich Array. We measure a scatter in mass at fixed $Y_{sph}$ of $\sim16\%$ at $Δ=500$, which is consistent with theoretical predictions of $\sim10-15\%$ scatter.

astro-ph.CO↗

arXiv2014

Chandra ACIS-I particle background: an analytical model

Aims: Imaging and spectroscopy of X-ray extended sources require a proper characterisation of a spatially unresolved background signal. This background includes sky and instrumental components, each of which are characterised by its proper spatial and spectral behaviour. While the X-ray sky background has been extensively studied in previous work, here we analyse and model the instrumental background of the ACIS-I detector on-board the Chandra X-ray observatory in very faint mode. Methods: Caused by interaction of highly energetic particles with the detector, the ACIS-I instrumental background is spectrally characterised by the superposition of several fluorescence emission lines onto a continuum. To isolate its flux from any sky component, we fitted an analytical model of the continuum to observations performed in very faint mode with the detector in the stowed position shielded from the sky, and gathered over the eight year period starting in 2001. The remaining emission lines were fitted to blank-sky observations of the same period. We found 11 emission lines. Analysing the spatial variation of the amplitude, energy and width of these lines has further allowed us to infer that three lines of these are presumably due to an energy correction artefact produced in the frame store. Results: We provide an analytical model that predicts the instrumental background with a precision of 2% in the continuum and 5% in the lines. We use this model to measure the flux of the unresolved cosmic X-ray background in the Chandra deep field south. We obtain a flux of $10.2^{+0.5}_{-0.4} \times 10^{13}$ $erg$ $cm^{-2} deg^{-2} s^{-1}$ for the $[1-2]$ keV band and $(3.8 \pm 0.2) \times 10^{12}$ $erg$ $cm^{-2} deg^{-2} s^{-1}$ for the $[2-8]$ keV band.

astro-ph.IM↗

arXiv2013

The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics.

astro-ph.HE↗