Abstract
Here we present Halo-FDCA, a robust open source Python package for modeling and estimating total flux densities of radio (mini) halos in galaxy clusters. Radio halos are extended ( ~200 - 1500 kpc in size) synchrotron emitting sources found in galaxy clusters that trace the presence of cosmic rays and magnetic fields in the intracluster medium (ICM). These sources are centrally located and have a low surface brightness. Their exact origin is still unknown but they are likely related to cosmic rays being re-accelerated in-situ by merger or sloshing driven ICM turbulence. The presented algorithm combines the numerical power of the Markov Chain Monte Carlo routine and multiple theoretical models to estimate the total radio flux density of a radio halo from a radio image and its associated uncertainty. This method introduces a flexible analytic fitting procedure to replace existing simplistic manual measurements prone to biases and inaccuracies. It allows to easily determine the properties of the emission and is particularly suitable for future studies of large samples of clusters.
Highlights
Galaxy clusters are massive gravitationally bound systems consisting of hundreds to thousands of individual galaxies and have total masses of the order of ∼ 1014−15 M⊙
More than 100 diffuse radio sources in the intracluster medium (ICM) are known and their number is increasing rapidly due to recent advances of low-frequency radio telescopes and surveys (e.g., Jonas, 2009; Norris et al, 2011; van Haarlem et al, 2013; Duchesne et al, 2017; Hurley-Walker et al, 2017; Shimwell et al, 2017; Shimwell et al, 2019; Gupta et al, 2017; de Gasperin et al, 2021)
The main objective in this work is to develop a robust model to fit the flux density profiles of radio halos in galaxy clusters which results in a generic algorithm functioning with a little user input, limiting the biases introduced by manual measurements
Summary
Galaxy clusters are massive gravitationally bound systems consisting of hundreds to thousands of individual galaxies and have total masses of the order of ∼ 1014−15 M⊙. Using large samples of radio halos we can study their statistical properties, such as how the total power and emissivity in the cluster’s volume scale with cluster mass. These quantities form an important basis to test theoretical models for the formation of diffuse sources in the ICM. Measured values in the literature often adopt a boundary of the radio emission based on a certain contour level determined by the noise of the radio image This means that the sizes and integrated flux densities do depend on the map noise and grow when deeper observations are available. The main objective in this work is to develop a robust model to fit the flux density profiles of radio halos in galaxy clusters which results in a generic algorithm functioning with a little user input, limiting the biases introduced by manual measurements
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