Understanding `galaxy groups' as a unique structure in the universe

Abstract

`Galaxy groups' have hardly been realised as a separate class of objects with specific characteristics in the structural hierarchy. The presumption that the self-similarity of dark matter structures is a valid prescription for the baryonic universe at all scales has rendered smaller structures undetectable by current observational facilities, leading to lesser dedicated studies on them. Some recent reports that indicate a deviation from ${\mathrm{L}}_{\mathrm{x}}$-T scaling in groups compared to clusters have motivated us to study their physical properties in depth. In this article, we report the extensive study on physical properties of groups in comparison to the clusters through cosmological hydrodynamic plus N-body simulations using ENZO 2.2 code. As additional physics, radiative cooling, heating due to supernova and star motions, star formation and stellar feedback has been implemented. We have produced a mock sample of 362 objects with mass ranging from $5\times 10^{12}{\mathrm{M}}_{\odot }$ to 2.5$\times 10^{15}{\mathrm{M}}_{\odot }$. Strikingly, we have found that objects with mass below $\sim$ $8\times 10^{13}{\mathrm{M}}_{\odot }$ do not follow any of the cluster self-similar laws in hydrostatics, not even in thermal and non-thermal energies. Two distinct scaling laws are observed to be followed with breaks at $\sim$ $8\times 10^{13}{\mathrm{M}}_{\odot }$ for mass, $\sim$1 keV for temperature and $\sim$1 Mpc for radius. This places groups as a distinct entity in the hierarchical structures, well demarcated from clusters. This study reveals that groups are mostly far away from virialization, suggesting the need for formulating new models for deciphering their physical parameters. They are also shown to have high turbulence and more non-thermal energy stored, indicating better visibility in the non-thermal regime.

11 pages, 11 figures, Accepted for publication in MNRAS

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Cited by in corpus (7)

• Joint Suzaku and Chandra observations of the MKW4 galaxy group out to the virial radius
• SZ Scaling Relations of Galaxy Groups and Clusters Near the North Ecliptic Pole
• uGMRT detection of cluster radio emission in low-mass Planck~SZ clusters
• Radio-relic and the diffuse emission trail discovered in a low mass galaxy cluster Abell 1697
• Somewhere in between: Tracing the Radio Emission from Galaxy Groups (or Why Does the Future of Observing Galaxy Groups with Radio Telescopes Look Promising?)
• Adaptive friends-of-friends algorithm for identifying gravitationally bound cosmological structures
• Turbulence in the intragroup and circumgalactic medium