[Paper Review] A multi-wavelength analysis of the cluster of galaxies ABCG 194

E. H. Nikogossyan, F. Durret+2 more|arXiv (Cornell University)|Jul 29, 1999

Astronomy and Astrophysical Research1 references3 citations

TL;DR

This study presents a multi-wavelength analysis of the poor, relaxed cluster ABCG 194 using optical, X-ray (ROSAT PSPC), and radio data. It reveals a linear morphology at small scales due to a low axial ratio (0.2 in the core), a small velocity dispersion (σₗₒₛ = 360 km/s), and absence of large-scale substructures, indicating a cold, dynamically relaxed system despite its linear appearance in the central region.

ABSTRACT

(Abridged) We present a morphological and structural analysis of the Richness zero cluster ABCG 194, known as a ``linear cluster'', based on a catalogue of 97 galaxies with B magnitudes and redshifts, a ROSAT PSPC image and radio data. The overall large scale structure is rather smooth and comparable at optical and X-ray wavelengths. The cluster is elongated along PA $\approx 50$; however it appears as ``linear'' when taking into account only galaxies in the very central part (the axial ratio varies from 0.2 in the central region to 0.8 for a larger region). We have obtained the galaxy and X-ray emitting gas density profiles and estimated the X-ray gas and dynamical masses. At smaller scales, the analysis of both positions and velocities reveals the existence of several groups; a main structure with a nearly gaussian velocity distribution is exhibited. The velocity dispersion is small ($σ_{los} $ = 360 \kms). A wavelet analysis of the X-ray image reveals no large scale substructures. Small scale X-ray sources are detected, mainly corresponding to individual galaxies. ABCG 194 is overall a poor and cold relaxed cluster. We compare how its characteristics fit into various correlations found in the literature, but generally for richer/hotter clusters.

Motivation & Objective

• Understand the structural and dynamical properties of the poor, richness-zero cluster ABCG 194, known for its linear morphology.
• Assess the consistency of optical and X-ray morphologies to determine the cluster's dynamical state.
• Investigate the presence of substructures and group-like features using galaxy positions and redshifts.
• Compare the cluster's characteristics with established scaling relations derived for richer, hotter clusters.
• Analyze X-ray surface brightness and density profiles to estimate gas and dynamical masses.

Proposed method

• Compiled a catalogue of 97 galaxies with B magnitudes and redshifts to map the optical structure and kinematics.
• Analyzed ROSAT PSPC X-ray image to derive surface brightness and gas density profiles.
• Applied wavelet analysis to the X-ray image to detect substructures at different spatial scales.
• Calculated galaxy and X-ray gas density profiles to estimate X-ray gas and dynamical masses.
• Used velocity dispersion (σₗₒₛ) to assess the dynamical state and temperature of the cluster.
• Compared observed properties with theoretical scaling relations for clusters of galaxies.

Experimental results

Research questions

• RQ1 What causes the apparent linear morphology of ABCG 194, and is it a real large-scale structure or an artifact of projection effects?
• RQ2 Does the cluster exhibit large-scale or small-scale substructures in X-ray and optical data?
• RQ3 How does the velocity dispersion and mass distribution of ABCG 194 compare to typical cluster scaling relations?
• RQ4 Is the cluster dynamically relaxed, and what evidence supports this conclusion?
• RQ5 Are there multiple group-like structures within ABCG 194, as indicated by velocity and spatial clustering?

Key findings

• ABCG 194 exhibits a linear appearance only in the central region, with an axial ratio of 0.2, but becomes more spherical (axial ratio 0.8) when larger scales are considered.
• The cluster has a low line-of-sight velocity dispersion of 360 km/s, indicating a cold, dynamically relaxed system.
• Wavelet analysis of the X-ray image reveals no large-scale substructures, supporting the relaxed nature of the cluster.
• Small-scale X-ray sources are predominantly associated with individual galaxies, not extended cluster emission.
• The X-ray gas and dynamical mass estimates are consistent with a poor, low-mass cluster, but the cluster does not fully align with scaling relations derived for richer, hotter clusters.
• Despite its linear appearance, ABCG 194 is overall a smooth, relaxed, and poor cluster with no significant large-scale substructure.