The gravitational field of X-COP galaxy clusters

Abstract

The mass profiles of massive dark matter halos are highly sensitive to the nature of dark matter and potential modifications of the theory of gravity on large scales. The Λ cold dark matter (CDM) paradigm makes strong predictions on the shape of dark matter halos and on the dependence of the shape parameters on halo mass, such that any deviation from the predicted universal shape would have important implications for the fundamental properties of dark matter. Here we use a set of 12 galaxy clusters with available deep X-ray and Sunyaev–Zel’dovich data to constrain the shape of the gravitational field with an unprecedented level of precision over two decades in radius. We introduce a nonparametric framework to reconstruct the shape of the gravitational field under the assumption of hydrostatic equilibrium and compare the resulting mass profiles to the expectations of Navarro–Frenk–White (NFW) and Einasto parametric mass profiles. On average, we find that the NFW profile provides an excellent description of the recovered mass profiles, with deviations of less than 10% over a wide radial range. However, there appears to be more diversity in the shape of individual profiles than can be captured by the NFW model. The average NFW concentration and its scatter agree very well with the prediction of the ΛCDM framework. For a subset of systems, we disentangle the gravitational field into the contribution of baryonic components (gas, brightest cluster galaxy, and satellite galaxies) and that of dark matter. The stellar content dominates the gravitational field inside ∼0.02R500 but is responsible for only 1–2% of the total gravitational field inside R200. The total baryon fraction reaches the cosmic value at R200 and slightly exceeds it beyond this point, possibly indicating a mild level of nonthermal pressure support (10 − 20%) in cluster outskirts. Finally, the relation between observed and baryonic acceleration exhibits a complex shape that strongly departs from the radial acceleration relation in spiral galaxies, which shows that the aforementioned relation does not hold at the galaxy-cluster scale.

X-ray analysis of JWST’s first galaxy cluster lens SMACS J0723.3−7327

“…Not only is the normalization of acceleration higher than what is found for galaxies (e.g., Tian et al 2020), but also the overall shape of the observed cluster RAR clearly deviates from the model in Eq. 4, implying a completely different RAR between clusters and galaxies (e.g., Eckert et al 2022;Tam et al 2022).…”

“…We thus ignore the core with a size of 200 kpc in the following discussion. Beyond the core, the contribution of stellar mass in the total mass budget is roughly a constant at ∼ 2% up to 2.5 Mpc (see, e.g., Andreon 2015;Eckert et al 2022). Therefore, we approximate the stellar mass profile M * (r) as 0.02 × M tot (r), adding on a systematic uncertainty of 50%.…”

i(cm)z, a semi-analytic model for the thermodynamic properties in galaxy clusters: Calibrations with mass and redshift, and implication for the hydrostatic bias

“…6, we have validated the i(cm)z model as a reliable indicator of the level of hydrostatic bias present in the total mass reconstruction. By applying the technique to the X-COP objects, a sample that offers high-quality data from which a detailed analysis of their hydrostatic mass profile has been produced (Ettori et al 2019;Eckert et al 2022), we assessed a level of hydrostatic bias quite in agreement with the current available constraints based on completely different assumptions (e.g., an universal gas mass fraction of reference; see Eckert et al 2019;.…”

“…The crosses show the predicted values from the revised scaling laws (orange, f g ; purple, T sl ; and green, L bol ). We further considered the role of the universal pressure profile, in particular, by estimating a profile through a joint fit of the X-COP nonparametric deprojected points from the recent analysis in Eckert et al (2022) and including the corrections due to the nonthermal pressure to M 500 (and, consequently, to R 500 ) from Fig. 7.…”

“…The dotted red lines are the predicted self-similar slopes, and the dashed blue lines correspond to the expected slopes from the i(cm)z model. Rescaled pressure profiles for the X-COP objects after the analyses in Eckert et al (2019Eckert et al ( , 2022. We note that M 500 and the relative R 500 were obtained after the correction for the estimated contribution from the nonthermal pressure (see Eckert et al 2019, for details).…”