Understanding ‘galaxy groups’ as a unique structure in the universe

Abstract

ABSTRACT'Galaxy groups' have hardly been realised as a separate class of objects with specific characteristics in the structural hierarchy. The presumption that the selfsimilarity 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 L 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 × 10 12 M to 2.5×10 15 M . Strikingly, we have found that objects with mass below ∼ 8 × 10 13 M 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 ∼ 8 × 10 13 M for mass, ∼1 keV for temperature and ∼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.

Entropic Uncertainty Principle, Partition Function and Holographic Principle derived from Liouville's Theorem

“…The Schrödinger Equation is normalised as is conventional by the probability factor |Ψ| 2 ; similarly, the entropic Partition Function defines the normalisation factor Z S (see below, Eqs. 16,17). The negative sign is also consistent with the entropic Partition Function itself being in a maximum entropy configuration described by a negative exponential distribution.…”

“…PJ2019 have proved the applicability of the QGT formalism to the double helix (evidenced by DNA), and the logarithmic double spiral (the spirae mirabiles of Bernoulli; evidenced by spiral galaxies); and Parker & Jeynes [ref.13] have also proved its applicability to spheres (evidenced by Buckminster-fullerene). Other entropic geometries of relevance in the universe include the large-scale filamental (dendritic) structure of galaxy groups and clusters with self-similar scaling relations investigated by Paul et al (2017). 17 The interaction of these structures with the high-entropy cosmic microwave background radiation is currently the object of intense investigation, for example by Hurier & Lacasa (2017).…”

“…Other entropic geometries of relevance in the universe include the large-scale filamental (dendritic) structure of galaxy groups and clusters with self-similar scaling relations investigated by Paul et al (2017). 17 The interaction of these structures with the high-entropy cosmic microwave background radiation is currently the object of intense investigation, for example by Hurier & Lacasa (2017). 18 Structures such as neural networks (used for deep learning and artificial intelligence applications and frequently featuring intermediate 'hidden' layers) also have a strongly dendritic organisational structure (with feedforward and feedback elements), allowing complex and adaptable interconnections between the input and output planes (synapses) of the system.…”

Total mass beyond r200 for systems with different density profile laws within a Λ background

“…For example, small groups are likely still in the collapse phase (e.g. Byrd & Valtonen ; Paul et al ), and while their virialized innermost part is well described by the NFW profile, the potential well and the concentration of the central regions should differ from those of virialized systems. Plausibly, they are described by a density distribution with a lower concentration.…”

Somewhere in between: Tracing the Radio Emission from Galaxy Groups (or Why Does the Future of Observing Galaxy Groups with Radio Telescopes Look Promising?)

“…Another important study exploring the uniqueness of the group environment is that of Paul et al [21]. These authors analyse a mock catalogue of systems of galaxies that differ in mass, radius, and temperature.…”