# HICOSMO - Cosmology with a complete sample of galaxy clusters: I. Data analysis, sample selection and luminosity-mass scaling-relation

## TL;DR

This study analyzes a complete sample of galaxy clusters using X-ray data to accurately estimate their masses, compare different mass measurement methods, and examine the luminosity-mass relation to improve cosmological parameter constraints.

## Contribution

It presents a detailed data analysis pipeline for X-ray cluster observations, compares hydrostatic, dynamical, and SZ masses, and investigates the luminosity-mass scaling relation with a focus on systematic biases.

## Key findings

- Good agreement between hydrostatic and dynamical masses.
- Planck SZ masses show a mass-dependent bias.
- Luminosity-mass relation slope is consistent with literature, with differences between groups and clusters.

## Abstract

The X-ray regime, where the most massive visible component of galaxy clusters, the intra cluster medium (ICM), is visible, offers directly measured quantities, like the luminosity, and derived quantities, like the total mass, to characterize these objects. The aim of this project is to analyze a complete sample of galaxy clusters in detail and constrain cosmological parameters, like the matter density, OmegaM, or the amplitude of initial density fluctuations, sigma8. The purely X-ray flux-limited sample (HIFLUGCS) consists of the 64 X-ray brightest galaxy clusters, which are excellent targets to study the systematic effects, that can bias results. We analyzed in total 196 Chandra observations of the 64 HIFLUGCS clusters, with a total exposure time of 7.7 Ms. Here we present our data analysis procedure (including an automated substructure detection and an energy band optimization for surface brightness profile analysis) which gives individually determined, robust total mass estimates. These masses are tested against dynamical and Planck Sunyaev-Zeldovich (SZ) derived masses of the same clusters, where good overall agreement is found with the dynamical masses. The Planck SZ masses seem to show a mass dependent bias to our hydrostatic masses; possible biases in this mass-mass comparison are discussed including the Planck selection function. Furthermore, we show the results for the 0.1-2.4-keV-luminosity vs. mass scaling-relation. The overall slope of the sample (1.34) is in agreement with expectations and values from literature. Splitting the sample into galaxy groups and clusters reveals, even after a selection bias correction, that galaxy groups exhibit a significantly steeper slope (1.88) compared to clusters (1.06).