Magnetic Field Strengths and Variations in Grain Alignment in the Local Bubble Wall

Optical and infrared continuum polarization from the interstellar medium is known to generally be due to irregular dust grains aligned with the magnetic field. This provides an important tool to probe the geometry and strength of those fields, particularly if the variations in the grain alignment ef...

Full description

Saved in:
Bibliographic Details
Published in:The Astrophysical journal 2019-03, Vol.873 (1), p.87
Main Authors: Medan, Ilija, Andersson, B-G
Format: Article
Language:English
Subjects:
Alignment
Astrophysics
Bubbles
Compressive strength
dust, extinction
Field strength
Interstellar matter
Interstellar medium
ISM: clouds
ISM: magnetic fields
Magnetic fields
Mapping
Polarization
Radiation
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Optical and infrared continuum polarization from the interstellar medium is known to generally be due to irregular dust grains aligned with the magnetic field. This provides an important tool to probe the geometry and strength of those fields, particularly if the variations in the grain alignment efficiencies can be understood. Here, we examine polarization variations observed throughout the wall of the Local Bubble, using a large polarization survey of the North Galactic cap (b > 30°) from Berdyugin et al. These data are analyzed together with archival photometric and spectroscopic data along with the mapping of the Local Bubble by Lallement et al. We can model the observational data by assuming that the mechanism driving alignment is due to the radiation from the surrounding star field. In particular we find that the fractional polarization is dominated by the light from the OB associations within 200 pc of the Sun, but is largely insensitive to the radiation field from red field stars. This behavior is consistent with the expected wavelength dependence of radiative grain alignment theory. We also probe the relative strength of the magnetic field in the wall of the Local Bubble using the Davis-Chandrasekhar-Fermi method. We find evidence for a systematically varying field strength distribution, where the variations in the field are correlated with the variations in grain alignment efficiency, indicating that the regions of relatively higher field strength might represent a compression of the wall by the interaction of the outflow in the Local Bubble and the opposing flows from the surrounding OB associations.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ab063c