Janusz Krywult

Morphology and evolution of simulated and optical clusters: a comparative analysis

We have made a comparative study of morphological evolution in simulated dark matter (DM) haloes and X-ray brightness distribution, and in optical clusters. Samples of simulated clusters include star formation with supernovae feedback, radiative cooling and simulation in the adiabatic limit at three different redshifts, z= 0.0, 0.10 and 0.25. The optical sample contains 208 Abell, Corwin & Olowin (ACO) clusters within redshift, z≤ 0.25. Cluster morphology, within 0.5 and 1.0 h−1 Mpc from cluster centre, is quantified by multiplicity and ellipticity. We find that the distribution of the DM haloes in the adiabatic simulation appears to be more elongated than the galaxy clusters. Radiative cooling brings halo shapes in excellent agreement with observed clusters; however, cooling along with feedback mechanism makes the haloes more flattened. Our results indicate relatively stronger structural evolution and more clumpy distributions in observed clusters than in the structure of simulated clusters, and slower increase in simulated cluster shapes compared to those in the observed one. Within z≤ 0.1, we note an interesting agreement in the shapes of clusters obtained from the cooling simulations and observation. We also note that the different samples of observed clusters differ significantly in morphological evolution with redshift. We highlight a few possibilities responsible for the discrepancy in morphological evolution of simulated and observed clusters.

The application of the Faint Object Classification and Analysis System (FOCAS) and Source Extractor (SExtractor) packages to the Digitized Sky Survey

In this paper the comparison between the Faint Object Classification and Analysis System (FOCAS) and Source Extractor (SExtractor) packages for automated star–galaxy classification is discussed. The analysis presented here uses a data set containing 43 Abell clusters of galaxies obtained from the Digitized Sky Survey. Comparison is based on four image parameters: the magnitude, area, ellipticity and position angle computed for each object. Statistical analysis shows that in the case of individual clusters, in general, there is good correlation between parameters obtained from both packages. The comparison of visual classification with automatic classification from FOCAS shows that the percentage of misclassified galaxies is about 20.

On the ellipticity of galaxy clusters

We analysed 246 scanned ACO clusters and we do not find any dependence of galaxy cluster ellipticity on redshift.