arXiv subjects

Diego F. González-Casanova

Publications and source records attributed to Diego F. González-Casanova.

4 recordsLinked to original sources

arXiv2019

Effects of the magnetic field direction on the Tsallis statistic

We extend the use of the Tsallis statistic to measure the differences in gas dynamics relative to the mean magnetic field present from natural eddy-type motions existing in magnetohydrodynamical (MHD) turbulence. The variation in gas dynamics was estimated using the Tsallis parameters on the incremental probability distribution function of the observables (intensity and velocity centroid) obtained from compressible MHD simulations. We find that the Tsallis statistic is susceptible to the anisotropy produce by the magnetic field, even when anisotropy is percent the Tsallis statistic can be use to determine MHD parameters such as the Sonic Mach number. We quantize the goodness of the Tsallis parameters using the coefficient of determination to measure the differences in the gas dynamics. These parameters also determine the level of magnetization and compressibility of the medium. To further simulate realistic spectroscopic observational data we introduced smoothing, noise, and cloud boundaries to the MHD simulations.

astro-ph.GA↗

arXiv2019

Velocity centroid gradients for absorbing media

We explore how the velocity gradient technique (VGT) can be applied to absorbing media in the case of$^{13}$CO 2-1 emission. The VGT is a new way to trace magnetic fields in the plane of the sky using only spectroscopic observations. We apply the VGT to magnetohydrodynamic turbulence simulations that have been post-processed to include $^{13}$CO 2-1 emission and we calculate the velocity centroid gradients. We find that the velocity centroid gradients trace the projected magnetic field in media with different $^{13}$CO abundances, densities and optical depths. Our study opens up the possibility of using velocity centroid gradients to trace magnetic fields in molecular clouds using 13CO emission.

astro-ph.GA↗

arXiv2016

Velocity Gradients as a Tracer for Magnetic Fields

Strong Alfvénic turbulence develops eddy-like motions perpendicular to the local direction of magnetic fields. This local alignment induces velocity gradients perpendicular to the local direction of the magnetic field. We use this fact to propose a new technique of studying the direction of magnetic fields from observations, the Velocity Gradient Technique. We test our idea by employing the synthetic observations obtained via 3D MHD numerical simulations for different sonic and Alfvén Mach numbers. We calculate the velocity gradient, $\mathbfΩ$, using the velocity centroids. We find that $\mathbfΩ$ traces the projected magnetic field best for the synthetic maps obtained with sub-Alfvénic simulations providing good point-wise correspondence between the magnetic field direction and that of $\mathbfΩ$. The reported alignment is much better than the alignment between the density gradients and the magnetic field and we demonstrated that it can be used to find the magnetic field strength using the Chandrasekhar-Fermi method. Our study opens a new way of studying magnetic fields using spectroscopic data.

astro-ph.GA↗

arXiv2016

Magnetic fields in early protostellar disk formation

We consider formation of accretion disks from a realistically turbulent molecular gas using 3D MHD simulations. In particular, we analyze the effect of the fast turbulent reconnection described by the Lazarian & Vishniac (1999) model for the removal of magnetic flux from a disk. With our numerical simulations we demonstrate how the fast reconnection enables protostellar disk formation resolving the so-called "magnetic braking catastrophe". In particular, we provide a detailed study of the dynamics of a 0.5 M$_\odot$ protostar and the formation of its disk for up to several thousands years. We measure the evolution of the mass, angular momentum, magnetic field, and turbulence around the star. We consider effects of two processes that strongly affect the magnetic transfer of angular momentum, both of which are based on turbulent reconnection: the first, "reconnection diffusion", removes the magnetic flux from the disk, the other involves the change of the magnetic field's topology, but does not change the absolute value of the magnetic flux through the disk. We demonstrate that for the first mechanism, turbulence causes a magnetic flux transport outward from the inner disk to the ambient medium, thus decreasing the coupling of the disk to the ambient material. A similar effect is achieved through the change of the magnetic field's topology from a split monopole configuration to a dipole configuration. We explore how both mechanisms prevent the catastrophic loss of disk angular momentum and compare both above turbulent reconnection mechanisms with alternative mechanisms from the literature.

astro-ph.SR↗