Details

Autor(en) / Beteiligte

• Hoang, Thiem
• Lazarian, A.

Titel

A UNIFIED MODEL OF GRAIN ALIGNMENT: RADIATIVE ALIGNMENT OF INTERSTELLAR GRAINS WITH MAGNETIC INCLUSIONS

Ist Teil von

• The Astrophysical journal, 2016-11, Vol.831 (2), p.159

Ort / Verlag

Philadelphia: The American Astronomical Society

Erscheinungsjahr

2016

Link zum Volltext

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• ABSTRACT The radiative torque (RAT) alignment of interstellar grains with ordinary paramagnetic susceptibilities has been supported by earlier studies. The alignment of such grains depends on the so-called RAT parameter qmax, which is determined by the grain shape. In this paper, we elaborate on our model of RAT alignment for grains with enhanced magnetic susceptibility due to iron inclusions, such that RAT alignment is magnetically enhanced, which we term the MRAT mechanism. Such grains can be aligned with high angular momentum at the so-called high-J attractor points, achieving a high degree of alignment. Using our analytical model of RATs, we derive the critical value of the magnetic relaxation parameter δm to produce high-J attractor points as functions of qmax and the anisotropic radiation angle relative to the magnetic field . We find that if about 10% of the total iron abundance present in silicate grains is forming iron clusters, this is sufficient to produce high-J attractor points for all reasonable values of qmax. To calculate the degree of grain alignment, we carry out numerical simulations of MRAT alignment by including stochastic excitations from gas collisions and magnetic fluctuations. We show that large grains can achieve perfect alignment when the high-J attractor point is present, regardless of the values of qmax. Our obtained results pave the way for the physical modeling of polarized thermal dust emission as well as magnetic dipole emission. We also find that millimeter-sized grains in accretion disks may be aligned with the magnetic field if they are incorporated with iron nanoparticles.