Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Particle-in-cell (PIC) simulations are used to examine the decay of strongly intermittent Alfvénic turbulence in a collisionless, homogeneous, and magnetized plasma. Results from three computational models are compared in simulations with similar plasma parameters and dimensions of approximately 100 <jats:italic>d</jats:italic> <jats:sub>i</jats:sub>, where <jats:italic>d</jats:italic> <jats:sub>i</jats:sub> is the ion inertial length. Each model utilizes three-dimensional velocities, but spatial variations differ: the 2.5D perpendicular PIC model uses two-dimensional spatial variations with the background magnetic field <jats:bold> <jats:italic>B</jats:italic> </jats:bold> <jats:sub>o</jats:sub> perpendicular to the simulation plane, the 2.5D parallel PIC model uses two-dimensional spatial variations with <jats:bold> <jats:italic>B</jats:italic> </jats:bold> <jats:sub>o</jats:sub> in the simulation plane, and the 3D model includes spatial variations in full three-dimensional space. Results from the three models are compared using plots of the joint probability distribution functions (PDFs) of maximum local linear instability growth rates versus the maximum local nonlinear frequencies. All results agree with previous demonstrations that linear growth rates are generally slower than the nonlinear frequencies of the turbulence at <jats:italic>kd</jats:italic> <jats:sub>i</jats:sub> = 1.0. However, it is the 3D PIC joint PDFs that most closely resemble joint PDFs recently observed in space plasmas because the 3D PDFs capture both the linear and nonlinear plasma processes, whereas the 2.5D parallel PIC runs do not represent the nonlinear turbulence processes and the 2.5D perpendicular PIC computations do not well represent the consequences of microinstabilities. These results suggest that 3D simulations are needed to properly capture important features of both microinstabilities and nonlinear turbulence.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetic fields in the intracluster medium affect the structure and the evolution of galaxy clusters. However, their properties are largely unknown, and measuring magnetic fields in galaxy clusters is challenging, especially on large scales outside of individual radio sources. In this work, we probe the plane-of-the-sky orientation of magnetic fields in clusters using the intensity gradients. The technique is a branch of the gradient technique (GT) that employs emission intensity maps from turbulent gas. We utilize Chandra X-ray images of the Perseus, M87, Coma, and A2597 galaxy clusters, and the VLA radio observations of the synchrotron emission from Perseus. We find that the fields predominantly follow the sloshing arms in Perseus, which is in agreement with numerical simulations. The GT-predicted magnetic field shows signatures of magnetic draping around rising bubbles driven by supermassive black hole feedback in the centers of cool-core clusters, as well as draping around substructures merging with the Coma cluster. We calculate the mean-field orientation with respect to the radial direction in these clusters. In the central regions of cool-core clusters, the mean orientation of the magnetic fields is preferentially azimuthal. There is broad agreement between the magnetic field of Perseus predicted using the X-ray and radio data. Further numerical studies and better future observations with higher resolution and larger effective area will help reduce the uncertainties of this method.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Supermassive black holes are commonly found at the centers of their host galaxies, but their formation still remains an open question. In light of the tight correlation between the black hole (BH) mass and the velocity dispersions of the bulge component of the host galaxy, a BH–host galaxy coevolution scenario has been established. Such a description, however, still contains many theoretical uncertainties, including puzzles about the formation of BH seeds at high redshifts and the growth channel fueling these seeds. In this work, we systematically analyze the signatures of different growth channels on massive BH (MBH) spins. We show that different growth channels can be partially distinguished with the magnitudes of MBH spins inferred from extreme-mass-ratio inspirals detected by the Laser Interferometer Space Antenna. In addition, we propose measuring the correlation between the directions of MBH spins and their host galaxy spins, which is possible for extreme-mass-ratio inspirals happening in low-redshift galaxies (<jats:inline-formula> <jats:tex-math> <?CDATA $z\leqslant 0.3$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb1b1ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>). With the inclusion of spin direction correlation different formation channels shall be significantly better constrained.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The secular behavior of an orbit under gravitational perturbation due to a two-dimensional uniform disk is studied in this paper, through analytical and numerical approaches. We develop the secular approximation of this problem and obtain the averaged Hamiltonian for this system first. We find that when the ratio of the semimajor axes of the inner orbit and the disk radius takes a very small value (≪1), and if the inclination between the inner orbit and the disk is greater than the critical value of 30°, the inner orbit will undergo the (classical) Lidov–Kozai resonance in which variations of eccentricity and inclination are usually very large and the system has two equilibrium points at <jats:italic>ω</jats:italic> = <jats:italic>π</jats:italic>/2, 3<jats:italic>π</jats:italic>/2 (<jats:italic>ω</jats:italic> is the argument of perihelion). The critical value will slightly drop to about 27° as the ratio increases to 0.4. However, the secular resonances will not occur for the outer orbit and the variations of the eccentricity and inclination are small. When the ratio of the orbit and the disk radius is nearly 1, there are many more complicated Lidov–Kozai resonance types which lead to orbital behaviors that are different from the classical Lidov–Kozai case. In these resonances, the system has more equilibrium points which could appear at <jats:italic>ω</jats:italic> = 0, <jats:italic>π</jats:italic>/2, <jats:italic>π</jats:italic>, 3<jats:italic>π</jats:italic>/2, and even other values of <jats:italic>ω</jats:italic>. The variations of eccentricity and inclination become relatively moderate, moreover, and in some cases the orbit can be maintained at a highly inclined state. In addition, an analysis shows that a Kuzmin disk can also lead to the (classical) Lidov–Kozai resonance, and the critical inclination is also 30°.</jats:p>