Abstract
High-resolution mapping of the intracluster medium (ICM) up to high redshift and down to low masses is crucial to derive accurate mass estimates of the galaxy cluster and to understand the systematic effects affecting cosmological studies based on galaxy clusters. We present a spatially resolved Sunyaev-Zel’dovich (SZ)/X-ray analysis of ACT-CL J0215.4+0030, a high-redshift (z = 0.865) galaxy cluster of intermediate mass (M500 ≃ 3.5 × 1014 M⊙) observed as part of the ongoing NIKA2 SZ large program, which is a follow-up of a representative sample of objects at 0.5 ≤ z ≤ 0.9. In addition to the faintness and small angular size induced by its mass and redshift, the cluster is contaminated by point sources that significantly affect the SZ signal. This is therefore an interesting case study for the most challenging sources of the NIKA2 cluster sample. We present the NIKA2 observations of this cluster and the resulting data. We identified the point sources that affect the NIKA2 maps of the cluster as submillimeter galaxies with counterparts in catalogs of sources constructed by the SPIRE instrument on board theHerschelobservatory. We reconstructed the ICM pressure profile by performing a joint analysis of the SZ signal and of the point-source component in the NIKA2 150 GHz map. This cluster is a very weak source that lies below the selection limit of thePlanckcatalog. Nonetheless, we obtained high-quality estimates of the ICM thermodynamical properties with NIKA2. We compared the pressure profile extracted from the NIKA2 map to the pressure profile obtained from X-ray data alone by deprojecting the publicXMM-Newtonobservations of the cluster. We combined the NIKA2 pressure profile with the X-ray deprojected density to extract detailed information on the ICM. The radial distribution of its thermodynamic properties (the pressure, temperature and entropy) indicate that the cluster has a highly disturbed core. We also computed the hydrostatic mass of the cluster, which is compatible with estimations from SZ and X-ray scaling relations. We conclude that the NIKA2 SZ large program can deliver quality information on the thermodynamics of the ICM even for one of its faintest clusters after a careful treatment of the contamination by point sources.
Highlights
As the last stage of hierarchical structure formation, galaxy clusters constitute the most massive gravitationally bound structures in the Universe
We present the study of the second observed cluster of the NIKA2 SZ large program, a high-resolution follow-up of 50 SZ-detected clusters at 0.5 ≤ z ≤ 0.9 from the Planck and ACT galaxy cluster catalogs (Planck Collaboration XXVII 2016; Hasselfield et al 2013)
Where I0 = 2(kBTCMB)3 ×−2 is the Cosmic microwave background (CMB) specific intensity, Te is the electron temperature of the intracluster medium (ICM), f (ν, Te) is the spectral dependence of the SZ effect, and y is the amplitude of the distortion, referred to as the Compton parameter, which is proportional to the line-of-sight integrated pressure of the ICM, y
Summary
As the last stage of hierarchical structure formation, galaxy clusters constitute the most massive gravitationally bound structures in the Universe. We present the study of the second observed cluster of the NIKA2 SZ large program, a high-resolution follow-up of 50 SZ-detected clusters at 0.5 ≤ z ≤ 0.9 from the Planck and ACT galaxy cluster catalogs (Planck Collaboration XXVII 2016; Hasselfield et al 2013). ACT-CL J0215.4+0030 has one of the lowest masses and highest redshifts in the large program sample, with M500 3.5 × 1014 M and z = 0.865 It was discovered by the Atacama Cosmology Telescope with a significance level of 5.5σ (Menanteau et al 2013; Hilton et al 2018, for the most recent data release), and is below the detection threshold in the Planck catalog (Planck Collaboration XXVII 2016).
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