Publications

• Tchernin, C., et al. 2016, A&A 595, 42, The XMM Cluster Outskirts Project (X-COP): Physical conditions of Abell 2142 up to the virial radius
  Pilot study demonstrating the potential of X-COP on the massive cluster A2142. The combination of X-ray and SZ data allows us to constrain thermodynamic properties and hydrostatic mass profiles in this cluster out to 3 Mpc. Our results highlight the importance of clumping beyond R500.
   ADS Link
   

• De Grandi, S., et al. 2016, A&A 592, 154, A textbook example of ram-pressure stripping in the Hydra A/A780 cluster 
  Discovery of a galaxy group with a mass of a few 1e13 solar masses falling into the Hydra A/A780 galaxy cluster. The stripping of the group's hot gas through the interaction with the main cluster induces a very long (~700 kpc) wake of hot gas following the motion of the gas. Our results set constraints on the properties of the intracluster plasma.
  ADS Link
   

• Ettori, S., et al. 2017, MNRAS 270, 29, Dark matter distribution in X-ray luminous galaxy clusters with Emergent Gravity
  Comparison between the mass profiles of two X-COP clusters, A2142 and A2319, and the prediction of emergent gravity theory as an alternative to dark matter. The shape of the mass profiles, however, significantly differs from the prediction of emergent gravity, which represents a challenge for the theory.
   ADS Link
   

• Eckert, D., et al. 2017, AN 338, 293, The XMM cluster outskirts project (X-COP)
  General paper presenting a global overview of the project. The main scientific goals of the project and the techniques that will be used to achieve these goals are presented. The sample selection is described and the basic properties of the selected clusters are provided. A2142 (Tchernin et al.) is used to illustrate the project.
  ADS Link
   

• Eckert, D., et al. 2017, A&A 605, 25, Deep Chandra observations of the stripped galaxy group falling into Abell 2142
  The infalling group in A2142, discovered in X-COP, is the poster child of accreting galaxy groups. A new deep Chandra observation of this feature revealed a very complex X-ray morphology, whereby the vast majority of the group's hot gas content has already been stripped. The morphology of the group suggests that transport processes in the ICM are highly suppressed and that the stripped gas is mildly turbulent.
  ADS Link
   

• Ghirardini, V. et al. 2018, A&A 614, 7, The XMM Cluster Outskirts Project (X-COP): Thermodynamic properties of the Intracluster Medium out to R200 in Abell 2319
  Application of the X-COP technique to the massive merging cluster A2319. The very high quality of the data allow us to measure the gas properties beyond the virial radius of this system. When scaled according to the mass measured using the hydrostatic equilibrium assumption, all the thermodynamic profiles deviate from the universal galaxy cluster profiles. The high gas fraction implies a substantial level of non-thermal pressure at the virial radius, at the level of ~40% of the total pressure.
  ArXiv preprint 
   

• Ghirardini, V. et al. 2019, A&A 621, 41, The universal thermodynamic properties of the intracluster medium over two decades in radius in the X-COP sample
  This paper presents for the first time average Universal thermodynamic properties (gas density, pressure, temperature, and entropy) of the intracluster medium out to the virial radius in a statistical sample. The results were compiled from the analysis of the full sample of 12 Planck-selected clusters. Once corrected for gas clumping, the entropy profiles of X-COP clusters agree with the predictions of gravitational collapse out to the largest radii probed in the study (2xR500). No statistically significant difference is found between relaxed (CC) and disturbed (NCC) clusters at R500 and beyond. We also present the scatter of the thermodynamic profiles around the sample average for all thermodynamic quantities.
  ArXiv preprint
   

• Ettori, S. et al. 2019, A&A 621, 39, Hydrostatic mass profiles in X-COP galaxy clusters
  Reconstruction of hydrostatic mass profiles from joint X-ray and SZ data for the full sample of 13 clusters. The very high quality of the X-COP data and the wide radial range probed in our project allow us to determine hydrostatic mass profiles with uncertainties of a few per cent in all systems. The standard Navarro-Frenk-White functional form provides the best fit to the data in the vast majority of cases, whereas models with a central core (Burkert, Isothermal sphere) are statistically disfavored. Modified gravity scenarios (MOND, Emergent Gravity) fail at reproducing the observed shape of galaxy cluster mass profiles.
  ArXiv preprint
   

• Eckert, D. et al. 2019, A&A 621, 40, Non-thermal pressure support in X-COP galaxy clusters
  Gas fraction profiles obtained through the assumption of hydrostatic equilibrium are presented. Assuming that the true gas fraction within the cluster's virial radius is known from numerical simulations, we derive the relative amount of non-thermal pressure required to match the measured hydrostatic gas fraction to the true one. The resulting non-thermal pressure fractions are low (6% at R500 and 10% at R200). The paper argues that a large hydrostatic bias as required to match CMB and cluster count cosmology is ruled out, unless the most massive clusters in the Universe are missing about a third of their baryons.
  ArXiv preprint
   

• Ghirardini, V. et al. 2019, A&A 627, 19, The polytropic state of the intracluster medium in the X-COP cluster sample
  A study of the polytropic stratification of the ICM through the relation between gas pressure and density. The X-COP data reveal a low-scatter, universal relation between these two fundamental quantities that is independent of a cluster's dynamical state. Beyond the cooling region (~0.2 R500), the measured polytropic relation agrees with the expectation for an ideal gas in hydrostatic equilibrium in a Navarro-Frenk-White potential.
  Arxiv preprint
   

• Baldi, A. S., et al. 2019, A&A 630, 121, Spectral imaging of the thermal Sunyaev-Zel'dovich effect in X-COP galaxy clusters: method and validation
  A new method for the spectral decomposition of the millimeter signal and reconstruction of thermal Sunyaev-Zeldovich maps from Planck data. The method builds a parametric spectral model for the main components (tSZ, CMB, dust, synchrotron), each of which is decomposed on a basis of wavelet and curvelet functions. The model is then convolved with the Planck beam and instrumental response at each frequency and fitted to the Planck images. Our new method highlights features at large radii in many X-COP clusters, in particular A2029 and RXC 1825. 
  Arxiv preprint
   

• Clavico, S., et al. 2019, A&A 632, 27, Growth and disruption in the Lyra complex
  A detailed analysis of the X-ray properties of the very active Lyra complex (RXC 1825 - CIZA 1824). Multiwavelength data (X-ray, optical and radio) show this is a rare quadruple merger, with the various components being in different stages of disruption. The main cluster (RXC 1825) shows clear signs of being in post-merger stage, while the subcluster (CIZA 1824) is relaxed and has not yet interacted. We also detect a compact source around a bright galaxy surrounded by a region of excess diffuse emission, which we associate with a galaxy group that has already crossed the main cluster. Overall, the Lyra complex is a striking example of structure formation at work, gathering much of the phenomenology that we can observe in the local cluster population.
  Arxiv preprint
   

• Ettori, S., et al. 2019, AN 341, 210, Helium abundance (and H0) in X-COP galaxy clusters
  While they probe the same physical phenomena, X-ray and SZ observations have different dependencies on the Helium abundance and on cosmological parameters (in particular H0). Comparing the same quantity (here, the pressure profile) measured with the two techniques, we can determine the Helium abundance in galaxy clusters as a function of H0. We found that a "canonical" value of the Helium abundance favors H0 = 70 km/s/Mpc, whereas the somewhat lower Planck value would imply an overabundance of Helium by about 35% with respect to the cosmic mean.
  Arxiv preprint
   

• Ghizzardi, S., et al. 2020, Submitted to A&A, Iron in X-COP: tracing enrichment in cluster outskirts with high accuracy abundance profiles
  A detailed study of iron abundance profiles in X-COP galaxy clusters from the core to R500. Using detailed numerical simulations we uncovered a previously unknown bias in iron abundance measurements in the background dominated regime, where the measurement tends to be done mostly through the Fe-L line complex around 1 keV rather than through the Fe-K complex around 6 keV. When excising the Fe-L complex, we found that Fe abundance profiles in X-COP clusters are remarkably flat and exhibit a very low scatter. We computed the total Fe mass within R500 and compare it with the Fe mass locked into stars. The amount of iron present within the ICM exceeds the Fe content of cluster galaxies by nearly an order of magnitude, which poses a challenge to chemical enrichment models.
  Arxiv preprint