Sub-structures in the hot gas atmosphere of galaxy clusters are related to their formation history and to the astrophysical processes at play in the intracluster medium ( ICM ) .
The thermal Sunyaev-Zel ’ dovich ( tSZ ) effect is directly sensitive to the line-of-sight integrated ICM pressure , and is thus particularly adapted to study ICM sub-structures .
In this paper , we apply structure-enhancement filtering algorithms to high resolution tSZ observations ( e.g .
NIKA ) of distant clusters , in order to search for pressure discontinuities , compressions , as well as secondary peaks in the ICM .
The same filters are applied to toy-model images and to synthetic tSZ images extracted from RHAPSODY-G cosmological hydrodynamic simulations , in order to better interpret the extracted features .
We also study the noise propagation trough the filters and quantify the impact of systematic effects , such as data processing induced artifacts and point source residuals , the latter being identified as the dominant potential contaminant .
In three of our six NIKA-observed clusters we identify features at high signal-to-noise that show clear evidence for merger events .
In MACS J0717.5+3745 ( z = 0.55 ) , three strong pressure gradients are observed on the east , southeast and west sectors , and two main peaks in the pressure distribution are identified .
We observe a lack of tSZ compact structure in the cool-core cluster PSZ1 G045.85+57.71 ( z = 0.61 ) , and a tSZ gradient ridge dominates in the southeast .
In the highest redshift cluster , CL J1226.9+3332 ( z = 0.89 ) , we detect a \sim 45 arcsec ( 360 kpc ) long ridge pressure gradient associated with a secondary pressure peak in the west region .
Our results show that current tSZ facilities have now reached the angular resolution and sensitivity to allow an exploration of the details of pressure sub-structures in clusters , even at high redshift .
This opens the possibility to quantify the impact of the dynamical state on the relation between the tSZ signal and the mass of clusters , which is important when using tSZ clusters to test cosmological models .
This work also marks the first NIKA cluster sample data release .