arXiv subjects

M. Khademi

Publications and source records attributed to M. Khademi.

3 recordsLinked to original sources

arXiv2023

Black hole solutions to Einstein-Bel-Robinson gravity

In this paper, we study the physical properties of black holes in the framework of the recently proposed Einstien-Bel-Robinson gravity. We show that interestingly the theory propagates a transverse and massive graviton on a maximally symmetric background with positive energy. There is also a single ghost-free branch that returns to the Einstein case when \beta\to 0. We find new black hole solutions to the equations, both approximate and exact, the latter being a constant curvature black hole solution, and discuss inconsistencies with metrics that were previously claimed to be approximate solutions to the equations. We obtain the conserved charges of the theory and briefly study the thermodynamics of the black hole solutions.

gr-qc↗

arXiv2023

Influence of Magnetic Fields on the Gas Rotation in the Galaxy $NGC\;6946$

Magnetic fields can play an important role in the energy balance and formation of gas structures in galaxies. However, their dynamical effect on the rotation curve of galaxies is immensely unexplored. We investigate the dynamical effect of the known magnetic arms of $NGC\;6946$ on its circular gas rotation traced in HI, considering two dark matter mass density models, ISO, and the universal NFW profile. We used a three-dimensional model for the magnetic field structure to fit the modeled rotation curve to the observed data via an $χ$-squared minimization method. The shape of the HI gas rotation curve is reproduced better including the effect of the magnetic field, especially in the outer part, where the dynamical effect of the magnetic field could become important. The typical amplitude of the regular magnetic field contribution in the rotation curve is about $ 6 - 14 \; km s^{-1}$ in the outer gaseous disk of the galaxy $NGC\;6946$. The contribution ratio of the regular magnetic field to the observed circular velocity and to dark matter increases with the galactocentric radius. Its ratio to the observed rotational velocity is about five percent and to dark matter is about 10 percent in the outer regions of the galaxy $NGC\;6946$. Therefore, the large-scale magnetic fields cannot be completely ignored in the large-scale dynamics of spiral galaxies, especially in the outer parts of galaxies.

astro-ph.GA↗

arXiv2021

Kinematical asymmetry in the dwarf irregular galaxy WLM and a perturbed halo potential

WLM is a dwarf irregular that is seen almost edge-on that has prompted a number of kinematical studies investigating its rotation curve and its dark matter content. In this paper, we investigate the origin of the strong asymmetry of the rotation curve, which shows a significant discrepancy between the approaching and the receding side. We first examine whether an $m = 1$ perturbation (lopsidedness) in the halo potential could be a mechanism creating such kinematical asymmetry. To do so, we fit a theoretical rotational velocity associated with an $m = 1$ perturbation in the halo potential model to the observed data via a $χ-$squared minimization method. We show that a lopsided halo potential model can explain the asymmetry in the kinematic data reasonably well. We then verify that the kinematical classification of WLM shows that its velocity field is significantly perturbed due to both its asymmetrical rotation curve and also its peculiar velocity dispersion map. In addition, based on a kinemetry analysis, we find that it is possible for WLM to lie in the transition region, where the disk and merger coexist. In conclusion, it appears that the rotation curve of WLM diverges significantly from that of an ideal rotating disk, which may significantly affect investigations of its dark matter content.

astro-ph.GA↗