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| Paper: |
Ground-state Alignment: New Magnetic Field Diagnostics in Diffuse Medium |
| Volume: |
449, Astronomical Polarimetry 2008: Science from Small to Large Telescopes |
| Page: |
139 |
| Authors: |
Yan, H.; Lazarian, A. |
| Abstract: |
We discuss a new technique of studying magnetic fields in diffuse astrophysical media, e.g.
interstellar and intergalactic gas/plasma. This technique is based on the
angular momentum alignment of atoms and ions in their ground or metastable states. As the lifetime
of atoms in such states is long, the alignment induced by anisotropic radiation
is susceptible to weak magnetic fields (1G > B> 0.1μG). The alignment
reveals itself in terms of the polarization of the absorbed and emitted light. A variety of atoms with
fine or hyperfine splitting of the ground or metastable states exhibit the alignment and the resulting
polarization degree in some cases exceeds 20%. We show that in the case of absorption the
polarization direction is either parallel or perpendicular to magnetic field, while more complex
dependencies emerge for the case of emission of aligned atoms. We show that the corresponding
studies of magnetic fields can be performed with optical and UV polarimetry. A unique feature of
these studies is that they can reveal the 3D orientation of magnetic field.
In addition, we point out that the polarization of the
radiation arising from the transitions between fine and hyperfine states of the ground level can provide yet another promising diagnostics of magnetic fields, including the magnetic fields in the Early Universe. We mention several cases of interplanetary, circumstellar and interstellar magnetic fields for which the studies of magnetic fields using ground state atomic alignment effect are promising. |
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