Open AccessSearching for cluster substructure using APM and ROSAT data
Author(s) -
Kolokotronis V.,
Basilakos S.,
Plionis M.,
Georgantopoulos I.
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.03924.x
Subject(s) - substructure , physics , rosat , cluster (spacecraft) , astrophysics , galaxy cluster , surface brightness , projection (relational algebra) , monte carlo method , galaxy , brightness , optics , algorithm , statistics , mathematics , structural engineering , computer science , engineering , programming language
We present a detailed study of the morphological features of 22 rich galaxy clusters. Our sample is constructed from a cross‐correlation of optical data with X‐ray (0.1–2.4 keV) ROSAT pointed observations. We systematically compare cluster images and morphological parameters in an attempt to reliably identify possible substructure in both optical and the X‐ray images. To this end, we compute various moments of the optical and X‐ray surface‐brightness distribution such as the ellipticities, centre‐of‐mass shifts and ellipsoidal orientations. We assess the significance of our results using Monte Carlo simulations. We find significant correlations between the optical and X‐ray morphological parameters, indicating that in both parts of the spectrum it is possible to identify correctly the dynamical state of a cluster. Most of our clusters (17/22) have a good one‐to‐one correspondence between the optical and the X‐ray images, and about 10 appear to have strong indications of substructure. This corresponds to a minimum percentage of order ∼45 per cent, which is in very good accordance with other similar analyses. Finally, five out of 22 systems (∼22 per cent) seem to have distinct subclumps in the optical which are not verified in the X‐ray images, and thus are suspect of being due to optical projection effects. These results will serve as a useful guide in interpreting subsequent analyses of large optical cluster catalogues.