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Magnetic fields, while ubiquitous in many astrophysical environments, are challenging to measure observationally. Based on the properties of anisotropy of eddies in magnetized turbulence, the velocity gradient technique is a method synergistic to dust polarimetry that is capable of tracing plane-of-the-sky magnetic fields, measuring the magnetization of interstellar media and estimating the fraction of gravitational collapsing gas in molecular clouds using spectral line observations. Here, we apply this technique to five low-mass star-forming molecular clouds in the Gould Belt and compare the results to the magnetic field orientation obtained from polarized dust emission. We find that the estimates of magnetic field orientations and magnetization for both methods are statistically similar. We estimate the fraction of collapsing gas in the selected clouds. By using the velocity gradient technique, we also present the plane-of-the-sky magnetic field orientation and magnetization of the Smith Cloud, for which dust polarimetry data are unavailable.The velocity gradient technique is used to measure the magnetic field orientations and magnetization of five low-mass star-forming molecular clouds, also finding that collapsing regions constitute a small fraction of the volume in these clouds.

Astrophysical fluids have very large Reynolds numbers and therefore turbulence is their natural state. Magnetic reconnection is an important process in many astrophysical plasmas, which allows restructuring of magnetic fields and conversion of stored magnetic energy into heat and kinetic energy. Turbulence is known to dramatically change different transport processes and therefore it is not unexpected that turbulence can alter the dynamics of magnetic field lines within the reconnection process. We shall review the interaction between turbulence and reconnection at different scales, showing how a state of turbulent reconnection is natural in astrophysical plasmas, with implications for a range of phenomena across astrophysics. We consider the process of magnetic reconnection that is fast in magnetohydrodynamic (MHD) limit and discuss how turbulence—both externally driven and generated in the reconnecting system—can make reconnection independent on the microphysical properties of plasmas. We will also show how relaxation theory can be used to calculate the energy dissipated in turbulent reconnecting fields. As well as heating the plasma, the energy dissipated by turbulent reconnection may cause acceleration of non-thermal particles, which is briefly discussed here.

Observations over the last few decades have shown that cosmic rays have a small non uniform distribution in arrival direction. Such anisotropy appears to have a roughly consistent topology between 10's GeV and 100's TeV, with a smooth energy dependency on phase and amplitude. However, above a few 100's TeV a sudden change in the topology of the anisotropy is observed. The cosmic ray arrival directions are expected to depend on the distribution of their sources in the Milky Way, as well as on effects arising from propagation in the inhomogeneous and turbulent interstellar magnetic field. In particular, in the 1-10 TeV energy range, the gyroradius of cosmic ray particles, much smaller that the injection scale of interstellar magnetic field turbulence, is comparable to the size of the heliosphere. Resonant scattering processes of cosmic ray particles propagating through the heliosphere may be able to induce a redistribution of the small anisotropic component of their flux. In this paper we discuss on the processes that occurs to TeV cosmic rays in the heliosphere and on the possibility to probe the heliospheric magnetic fields on large scale by studying the arrival distribution of cosmos rays.

Magnetohydrodynamic (MHD) turbulence is a critical component of the current paradigms of star formation, dynamo theory, particle transport, magnetic reconnection and evolution of the ISM. In order to gain understanding of how MHD turbulence regulates processes in the Galaxy, a confluence of numerics, observations and theory must be imployed. In these proceedings we review recent progress that has been made on the connections between theoretical, numerical, and observational understanding of MHD turbulence as it applies to both the neutral and ionized interstellar medium.

Interaction of three-dimensional magnetic fields, turbulence, and self-gravity in the molecular cloud is crucial in understanding star formation but has not been addressed so far. In this work, we target the low-mass star-forming region L1688 and use the spectral emissions of \\(^{12}\\)CO, \\(^{13}\\)CO, C\\(^{18}\\)O, and H I, as well as polarized dust emissions. To obtain the 3D direction of the magnetic field, we employ the novel polarization fraction analysis. In combining with the plane-of-the-sky (POS) magnetic field strength derived from the Davis-Chandrasekhar-Fermi (DCF) method and the new Differential Measure Analysis (DMA) technique, we present the first measurement of L1688's three-dimensional magnetic field, including its orientation and strength. We find that L1688's magnetic field has two statistically different inclination angles. The low-intensity tail has an inclination angle \\(\\approx55^\\circ\\) on average, while that of the central dense clump is \\(\\approx30^\\circ\\). We find the global mean value of total magnetic field strength is \\(B_{\\rm tot}\\approx135\\) uG from DCF and \\(B_{\\rm tot}\\approx75\\) uG from DMA. We use the velocity gradient technique (VGT) to separate the magnetic fields' POS orientation associated with L1688 and its foreground/background. The magnetic fields' orientations are statistically coherent. The probability density function of H\\(_2\\) column density and VGT reveal that L1688 is potentially undergoing gravitational contraction at large scale \\(\\approx1.0\\) pc and gravitational collapse at small scale \\(\\approx0.2\\) pc. The gravitational contraction mainly along the magnetic field results in an approximate power-law relation \\(B_{\\rm tot}\\propto n_{\\rm H}^{1/2}\\) when volume density \\(n_{\\rm H}\\) is less than approximately \\(6.0\\times10^3\\) cm\\(^{-3}\\).

The mapping of the Galactic Magnetic Field (GMF) in three dimensions is essential to comprehend various astrophysical processes that occur within the Milky Way. This study endeavors to map the GMF by utilizing the latest MM2 technique, the Velocity Gradient Technique (VGT), the Column Density Variance Approach, and the GALFA-H I survey of Neutral Hydrogen (H I) emission. The MM2 and VGT methods rely on an advanced understanding of magnetohydrodynamics turbulence to determine the magnetic field strength and orientation respectively. The H I emission data, combined with the Galactic rotational curve, gives us the distribution of H I gas throughout the Milky Way. By combining these two techniques, we map the GMF orientation and strength, as well as the Alfvén Mach number \\(M_{\\rm A}\\) in 3D for a low galactic latitude (\\(b<30^{\\rm o}\\)) region close to the Perseus Arm. The analysis of column density variance gives the sonic Mach number \\(M_{\\rm s}\\) distribution, The results of this study reveal the sub-Alfvénic and subsonic (or trans-sonic) nature of the H I gas. The variation of mean \\(M_{\\rm A}\\) along the line-of-sight approximately ranges from 0.6 to 0.9, while that of mean \\(M_{\\rm s}\\) is from 0.2 to 1.5. The mean magnetic field strength varies from ~0.5 \\(\\mu\\)G to ~2.5 \\(\\mu\\)G exhibiting a decreasing trend towards the Galaxy's outskirt. This work provides a new avenue for mapping the GMF, especially the magnetic field strength, in 3D. We discuss potential synergetic applications with other approaches.

The ubiquitous turbulence in astrophysical plasmas is important for both magnetic reconnection and reconnection acceleration. We study the particle acceleration during fast 3D turbulent reconnection with reconnection-driven turbulence. Particles bounce back and forth between the reconnection-driven inflows due to the mirror reflection and convergence of strong magnetic fields. Via successive head-on collisions, the kinetic energy of the inflows is converted into the accelerated particles. Turbulence not only regulates the inflow speed but also introduces various inflow obliquities with respect to the local turbulent magnetic fields. As both the energy gain and escape probability of particles depend on the inflow speed, the spectral index of particle energy spectrum is not universal. We find it in the range from \\(\\approx 2.5\\) to \\(4\\), with the steepest spectrum expected at a strong guide field, i.e. a small angle between the total incoming magnetic field and the guide field. Without scattering diffusion needed for confining particles, the reconnection acceleration can be very efficient at a large inflow speed and a weak guide field.

We study the streaming instability of GeV\\(-100~\\)GeV cosmic rays (CRs) and its damping in the turbulent interstellar medium (ISM). We find that the damping of streaming instability is dominated by ion-neutral collisional damping in weakly ionized molecular clouds, turbulent damping in the highly ionized warm medium, and nonlinear Landau damping in the Galactic halo. Only in the Galactic halo, is the streaming speed of CRs close to the Alfv\\'{e}n speed. Alfv\\'{e}nic turbulence plays an important role in both suppressing the streaming instability and regulating the diffusion of streaming CRs via magnetic field line tangling, with the effective mean free path of streaming CRs in the observer frame determined by the Alfv\\'{e}nic scale in super-Alfv\\'{e}nic turbulence. The resulting diffusion coefficient is sensitive to Alfv\\'{e}n Mach number, which has a large range of values in the multi-phase ISM. Super-Alfv\\'{e}nic turbulence contributes to additional confinement of streaming CRs, irrespective of the dominant damping mechanism.

We investigate shock acceleration in a realistic astrophysical environment with density inhomogeneities. The turbulence induced by the interaction of the shock precursor with upstream density fluctuations amplifies both upstream and downstream magnetic fields via the turbulent dynamo. The dynamo-amplified turbulent magnetic fields (a) introduce variations of shock obliquities along the shock face, (b) enable energy gain through a combination of shock drift and diffusive processes, (c) give rise to various spectral indices of accelerated particles, (d) regulate the diffusion of particles both parallel and perpendicular to the magnetic field, and (e) increase the shock acceleration efficiency. Our results demonstrate that upstream density inhomogeneities and dynamo amplification of magnetic fields play an important role in shock acceleration, and thus shock acceleration depends on the condition of the ambient interstellar environment. The implications on understanding radio spectra of supernova remnants are also discussed.