The XXL Survey. LI. Pressure profile and Y$_SZ$ ‒ M scaling relation in three low-mass galaxy clusters at z sim 1 observed with NIKA2

Context.
The thermodynamical properties of the intracluster medium (ICM) are driven by scale-free gravitational collapse, but they also reflect the rich astrophysical processes at play in galaxy clusters. At low masses (∼10¹⁴ M_⊙) and high redshift (z ≳ 1), these properties remain poorly constrained, observationally speaking, due to the difficulty in obtaining resolved and sensitive data.

Aims.
We aim to investigate the inner structure of the ICM as seen through the Sunyaev–Zel’dovich (SZ) effect in this regime of mass and redshift. We focused on the thermal pressure profile and the scaling relation between SZ flux and mass, namely the Y_SZ − M scaling relation.

Methods.
The three galaxy clusters XLSSC 072 (z = 1.002), XLSSC 100 (z = 0.915), and XLSSC 102 (z = 0.969), with M₅₀₀ ∼ 2 × 10¹⁴ M_⊙, were selected from the XXL X-ray survey and observed with the NIKA2 millimeter camera to image their SZ signal. XMM-Newton X-ray data were used as a complement to the NIKA2 data to derive masses based on the Y_X − M relation and the hydrostatic equilibrium.

Results.
The SZ images of the three clusters, along with the X-ray and optical data, indicate dynamical activity related to merging events. The pressure profile is consistent with that expected for morphologically disturbed systems, with a relatively flat core and a shallow outer slope. Despite significant disturbances in the ICM, the three high-redshift low-mass clusters follow the YSZ − M relation expected from standard evolution remarkably well.

Conclusions.
These results indicate that the dominant physics that drives cluster evolution is already in place by z ∼ 1, at least for systems with masses above M₅₀₀ ∼ 10¹⁴ M_⊙.