scholarly journals Barred spiral galaxies in modified gravity theories

2021 ◽  
Vol 503 (2) ◽  
pp. 2833-2860 ◽  
Author(s):  
Mahmood Roshan ◽  
Indranil Banik ◽  
Neda Ghafourian ◽  
Ingo Thies ◽  
Benoit Famaey ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Gravity Models ◽  
Dynamical Friction ◽  
Extended Gravity ◽  
Corotation Radius ◽  
Cosmological Context ◽  
Gravity Theories ◽  
Barred Spiral Galaxies ◽  
Pattern Speeds ◽  
Almost All

ABSTRACT When bars form within galaxy formation simulations in the standard cosmological context, dynamical friction with dark matter (DM) causes them to rotate rather slowly. However, almost all observed galactic bars are fast in terms of the ratio between corotation radius and bar length. Here, we explicitly display an 8σ tension between the observed distribution of this ratio and that in the EAGLE simulation at redshift 0. We also compare the evolution of Newtonian galactic discs embedded in DM haloes to their evolution in three extended gravity theories: Milgromian Dynamics (MOND), a model of non-local gravity, and a scalar–tensor–vector gravity theory (MOG). Although our models start with the same initial baryonic distribution and rotation curve, the long-term evolution is different. The bar instability happens more violently in MOND compared to the other models. There are some common features between the extended gravity models, in particular the negligible role played by dynamical friction − which plays a key role in the DM model. Partly for this reason, all extended gravity models predict weaker bars and faster bar pattern speeds compared to the DM case. Although the absence of strong bars in our idealized, isolated extended gravity simulations is in tension with observations, they reproduce the strong observational preference for ‘fast’ bar pattern speeds, which we could not do with DM. We confirm previous findings that apparently ‘ultrafast’ bars can be due to bar-spiral arm alignment leading to an overestimated bar length, especially in extended gravity scenarios where the bar is already fast.

scholarly journals Fast galaxy bars continue to challenge standard cosmology

2021 ◽  
Vol 508 (1) ◽  
pp. 926-939
Author(s):  
Mahmood Roshan ◽  
Neda Ghafourian ◽  
Tahere Kashfi ◽  
Indranil Banik ◽  
Moritz Haslbauer ◽  
...  
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Dark Matter Halo ◽  
Dynamical Friction ◽  
Statistical Population ◽  
Barred Galaxies ◽  
Corotation Radius ◽  
Pattern Speeds ◽  
Hydrodynamical Simulations ◽  
Disc Galaxies

ABSTRACT Many observed disc galaxies harbour a central bar. In the standard cosmological paradigm, galactic bars should be slowed down by dynamical friction from the dark matter halo. This friction depends on the galaxy’s physical properties in a complex way, making it impossible to formulate analytically. Fortunately, cosmological hydrodynamical simulations provide an excellent statistical population of galaxies, letting us quantify how simulated galactic bars evolve within dark matter haloes. We measure bar strengths, lengths, and pattern speeds in barred galaxies in state-of-the-art cosmological hydrodynamical simulations of the IllustrisTNG and EAGLE projects, using techniques similar to those used observationally. We then compare our results with the largest available observational sample at redshift z = 0. We show that the tension between these simulations and observations in the ratio of corotation radius to bar length is 12.62σ (TNG50), 13.56σ (TNG100), 2.94σ (EAGLE50), and 9.69σ (EAGLE100), revealing for the first time that the significant tension reported previously persists in the recently released TNG50. The lower statistical tension in EAGLE50 is actually caused by it only having five galaxies suitable for our analysis, but all four simulations give similar statistics for the bar pattern speed distribution. In addition, the fraction of disc galaxies with bars is similar between TNG50 and TNG100, though somewhat above EAGLE100. The simulated bar fraction and its trend with stellar mass both differ greatly from observations. These dramatic disagreements cast serious doubt on whether galaxies actually have massive cold dark matter haloes, with their associated dynamical friction acting on galactic bars.

scholarly journals Fluctuations in galactic bar parameters due to bar–spiral interaction

2020 ◽  
Vol 497 (1) ◽  
pp. 933-955 ◽  
Author(s):  
T Hilmi ◽  
I Minchev ◽  
T Buck ◽  
M Martig ◽  
A C Quillen ◽  
...  
Keyword(s):  
Late Time ◽  
Corotation Radius ◽  
Cosmological Context ◽  
Direct Measurements ◽  
Central Regions ◽  
Dynamical Time ◽  
External Galaxies ◽  
Pattern Speed ◽  
Structure Strength ◽  
Pattern Speeds

ABSTRACT We study the late-time evolution of the central regions of two Milky Way (MW)-like simulations of galaxies formed in a cosmological context, one hosting a fast bar and the other a slow one. We find that bar length, Rb, measurements fluctuate on a dynamical time-scale by up to 100 per cent, depending on the spiral structure strength and measurement threshold. The bar amplitude oscillates by about 15 per cent, correlating with Rb. The Tremaine–Weinberg method estimates of the bars’ instantaneous pattern speeds show variations around the mean of up to $\sim \!20{{\ \rm per\ cent}}$, typically anticorrelating with the bar length and strength. Through power spectrum analyses, we establish that these bar pulsations, with a period in the range ∼60–200 Myr, result from its interaction with multiple spiral modes, which are coupled with the bar. Because of the presence of odd spiral modes, the two bar halves typically do not connect at exactly the same time to a spiral arm, and their individual lengths can be significantly offset. We estimated that in about 50 per cent of bar measurements in MW-mass external galaxies, the bar lengths of SBab-type galaxies are overestimated by $\sim \!15{{\ \rm per\ cent}}$ and those of SBbc types by $\sim \!55{{\ \rm per\ cent}}$. Consequently, bars longer than their corotation radius reported in the literature, dubbed ‘ultrafast bars’, may simply correspond to the largest biases. Given that the Scutum–Centaurus arm is likely connected to the near half of the MW bar, recent direct measurements may be overestimating its length by 1–1.5 kpc, while its present pattern speed may be 5–10 $\rm km\ s^{-1}\ kpc^{-1}$ smaller than its time-averaged value.

scholarly journals Light bending in F[g(□)R] extended gravity theories

2018 ◽  
Vol 780 ◽  
pp. 54-60 ◽  
Author(s):  
Breno L. Giacchini ◽  
Ilya L. Shapiro
Keyword(s):  
Extended Gravity ◽  
Light Bending ◽  
Gravity Theories

Causality of 3D extended gravity theories

2019 ◽  
Vol 34 (16) ◽  
pp. 1950122
Author(s):  
Meguru Komada
Keyword(s):  
Shock Wave ◽  
Three Dimensional ◽  
Massive Gravity ◽  
Gravity Theory ◽  
Delay Effect ◽  
Fundamental Physics ◽  
Extended Gravity ◽  
3D Gravity ◽  
Gravity Theories ◽  
Time Delay Effect

Causality is one of the most important properties to understand gravity theories. It gives us not only a method to confirm that the gravity theories are really consistent, but also gives implications about the properties which unknown fundamental physics should obey. We investigate the causality of three-dimensional (3D) gravity theories, which are considered to be important, by using the Shapiro time delay effect in the Shock wave geometry. One of such gravity theories is the Zwei-Dreibein Gravity (ZDG) theory, which is a consistent 3D gravity theory. In ZDG theory, the serious problems can be removed that have appeared in another important gravity theory called New Massive Gravity (NMG). We study whether the ZDG theory could preserve the causality without losing the above good properties and how the causality structure is related to the structure of the NMG theory.

Networks of export markets and export market diversification

2020 ◽  
Author(s):  
Qi Guo ◽  
Shengjun Zhu ◽  
Ron Boschma
Keyword(s):  
Developed Countries ◽  
Gravity Models ◽  
Export Market ◽  
Gravity Effect ◽  
Export Markets ◽  
Policy Makers ◽  
Extended Gravity ◽  
Gravity Effects ◽  
Better Than ◽  
Developing And Developed Countries

Abstract In the era of globalization, policy makers in both developing and developed countries have sought to expand their export destinations, with the expectation that export market diversification can boost export upgrading and economic development. Although extant literature has confirmed that exporters search for new markets in two distinct ways: direct search underpinned by the gravity effect and remote search driven by the extended gravity effect, it has not advanced very far due to the lack of adequate measures of those effects. This article presents a technique that uses available export data to develop measures of those two effects that capture a larger range of factors and thus allow us to more easily predict export market diversification. Our new indicator also simplifies the prediction by combining gravity and extended gravity effects. Empirical results show that the explanatory and predictive power of our new method is better than that of the traditional one based on gravity and extended gravity models.

IMPROVEMENTS TO THE SPHERICAL COLLAPSE MODEL

2006 ◽  
Vol 15 (07) ◽  
pp. 1067-1088 ◽  
Author(s):  
ANTONINO DEL POPOLO
Keyword(s):  
Cosmological Constant ◽  
Galaxy Formation ◽  
Spherical Model ◽  
Mass Function ◽  
Joint Effect ◽  
Dynamical Friction ◽  
Spherical Collapse ◽  
Theoretical Mass ◽  
Collapse Model ◽  
Tidal Torques

We study the joint effect of dynamical friction, tidal torques and cosmological constant on clusters of galaxy formation. We show that within high-density environments, such as rich clusters of galaxies, both dynamical friction and tidal torques slow down the collapse of low-ν peaks producing an observable variation in the time of collapse of the perturbation and, as a consequence, a reduction in the mass bound to the collapsed perturbation. Moreover, the delay of the collapse produces a tendency for less dense regions to accrete less mass, with respect to a classical spherical model, inducing a biasing of over-dense regions toward higher mass. We show how the threshold of collapse is modified if dynamical friction, tidal torques and a non-zero cosmological constant are taken into account and we use the Extended Press–Schecter (EPS) approach to calculate the effects on the mass function. Then, we compare the numerical mass function given in D. Reed, Mon. Not. R. Astron. Soc.346, 565 (2003) with the theoretical mass function obtained in the present paper. We show that the barrier obtained in the present paper gives rise to a better description of the mass function evolution with respect to other previous models, R. K. Sheth and G. Tormen, Mon. Not. R. Astron. Soc.308, 119 (1999) and R. K. Sheth and G. Tormen, Mon. Not. R. Astron. Soc.329, 61 (2002).

scholarly journals Black Holes and Wormholes in Extended Gravity

Universe ◽  
2020 ◽  
Vol 6 (2) ◽  
pp. 25 ◽  
Author(s):  
Stanislav Alexeyev ◽  
Maxim Sendyuk
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Quantum Theory ◽  
Gravity Models ◽  
Astrophysical Data ◽  
Effective Gravity ◽  
Extended Gravity ◽  
Theory Of Gravity ◽  
Hawking Evaporation

We discuss black hole type solutions and wormhole type ones in the effective gravity models. Such models appear during the attempts to construct the quantum theory of gravity. The mentioned solutions, being, mostly, the perturbative generalisations of well-known ones in general relativity, carry out additional set of parameters and, therefore could help, for example, in the studying of the last stages of Hawking evaporation, in extracting the possibilities for the experimental or observational search and in helping to constrain by astrophysical data.

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