Galaxies

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Open AccessArticle

Characterization of Bars Induced by Interactions

by Inma Martinez-Valpuesta, José Alfonso López Aguerri and César González-García

Galaxies 2016, 4(2), 7; https://doi.org/10.3390/galaxies4020007 - 25 May 2016

Cited by 12 | Viewed by 3601

Whether the formation of bars is triggered by interactions or by internal processes has been discussed for many decades. In this work, we study differences between both mechanisms by means of numerical simulations. We relate our analysis to fly-by interactions in different mass [...] Read more.

Whether the formation of bars is triggered by interactions or by internal processes has been discussed for many decades. In this work, we study differences between both mechanisms by means of numerical simulations. We relate our analysis to fly-by interactions in different mass groups or clusters according to the velocity of the encounters. We find that once the bar is created, the interaction does not much affect its evolution. We also find that bars can be triggered purely by a slow interaction. Those bars affected or triggered by interaction stay for a longer time in the slow regime, i.e., the corotation radius is more than 1.4 times the bar radius. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

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243 KiB

Open AccessArticle

Theoretical Derivation of the Cosmological Constant in the Framework of the Hydrodynamic Model of Quantum Gravity: Can the Quantum Vacuum Singularity Be Overcome?

by Piero Chiarelli

Galaxies 2016, 4(2), 6; https://doi.org/10.3390/galaxies4020006 - 16 Apr 2016

Cited by 1 | Viewed by 3397

Abstract

In the present work, it is shown that the problem of the cosmological constant (CC) is practically the consequence of the inadequacy of general relativity to take into account the quantum property of the space. The equations show that the cosmological constant naturally [...] Read more.

In the present work, it is shown that the problem of the cosmological constant (CC) is practically the consequence of the inadequacy of general relativity to take into account the quantum property of the space. The equations show that the cosmological constant naturally emerges in the hydrodynamic formulation of quantum gravity and that it does not appear in the classical limit because the quantum energy-impulse tensor gives an equal contribution with opposite sign. The work shows that a very large local value of the CC comes from the space where the mass of a quasi-punctual particle is present but that it can be as small as measured on cosmological scale. The theory shows that the small dependence of the CC from the mean mass density of the universe is due to the null contribution coming from the empty space. This fact gives some hints for the explanation of the conundrum of the cosmic coincidence by making a high CC value of the initial instant of universe compatible with the very small one of the present era. Full article

8187 KiB

Open AccessArticle

Fossil Systems; a Multi-wavelength Approach towards Understanding Galaxy Formation

by Habib G. Khosroshahi, Halime Miraghaei and Mojtaba Raouf

Galaxies 2016, 4(2), 5; https://doi.org/10.3390/galaxies4020005 - 25 Mar 2016

Cited by 1 | Viewed by 3823

Abstract

Fossil systems are understood to be the end product of galaxy mergers within groups and clusters. Their halo morphology points to their relaxed/virialised nature, thus allowing them to be employed as observational probes for the evolution of cosmic structures, their thermodynamics and dark [...] Read more.

Fossil systems are understood to be the end product of galaxy mergers within groups and clusters. Their halo morphology points to their relaxed/virialised nature, thus allowing them to be employed as observational probes for the evolution of cosmic structures, their thermodynamics and dark matter distribution. Cosmological simulations, and their underlying models, are broadly consistent with the early formation epoch for fossils. In a series of studies we have looked into galaxy properties and intergalactic medium (IGM) in fossils, across a wide range of wavelengths, from X-ray through optical to the radio, to have a better understanding of their nature, the attributed halo age, IGM heating and their AGNs and use them as laboratories to constrain galaxy formation models. Adhering to one of less attended properties of fossils, using the the Millennium Simulation, we combine luminosity gap with luminosity segregation (the brightest galaxy offset from the group luminosity centroid) to identify the most dynamically relaxed galaxy groups which allows us to reveal brand new observational connections between galaxies and their environments. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

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Galaxies, Volume 4, Issue 2 (June 2016) – 3 articles

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