Magnetic Field Puzzles
description
Transcript of Magnetic Field Puzzles
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Magnetic Field Puzzles
From Our Own
Backyard
Jo-Anne Brown & Russ Taylor
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Outline
• Motivation • Probing the Galactic Magnetic Field • Puzzles and Potential Solutions
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•Magnetic fields are an integral part of the ISM. They...•...Contribute to the vertical support of gas in the Galaxy. •...Are essential in star formation. •...Influence galaxy formation and evolution.
•There remains many questions about our Galactic field:•What is its source?•How is it maintained?•How does it connect with the Inter-Galactic Medium?
•To answer these questions, we have to know what it looks like now!
Sales Pitch
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Galactic Magnetic Field Basics
• Two components: large, small• Concentrated in the disk• follows the spiral arms (?)• local field is cw• Sagittarius field is ccw• Determining the existence and location of additional reversals will help us understand the origin and evolution of the field - and possibly of the Galaxy itself!
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Faraday Rotation
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Comparing Pulsars to External Galaxies
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Available Data
~800 EGS + 1075 CGPS + 150 SGPS = 2025 EGS~555 Pulsars
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~120 EGS + 870 CGPS +150 SGPS = 1140 EGS~390 Pulsars
Available Data
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Available Data
~120 EGS + 870 CGPS +150 SGPS = 1140 EGS~390 Pulsars
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Arecibo is necessary to fill critical regions of Q1, Q3 and high latitudes.
Available Data
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Galactic Arecibo L-band Feed Array Continuum Transit Survey
GALFACTS
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Brown et al. 2003, ApJS, 145 (380 sources)
22 pulsars, 24 previous EGS and +1075 new RM sources in the CGPS region so far
CGPS RM sources:
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Brown et al. 2003, ApJS, 145 (380 sources)
22 pulsars, 24 previous EGS and +1075 new RM sources in the CGPS region so far
CGPS RM sources:
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SGPS RM sources:
120 pulsars, 1 previous EGS, 150 SGPS EGSBrown et al. 2007, ApJ, 663, 258 (148 sources)
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SGPS RM sources:
120 pulsars, 1 previous EGS, 150 SGPS EGSBrown et al. 2007, ApJ, 663, 258 (148 sources)
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Current GALFACTS RM sources:
36 pulsars; 20 EGS (2 CGPS EGS so far)...
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Anticipated GALFACTS RM sources:
Conservative estimate for GALFACTS sources in this region: +2000!
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Anticipated GALFACTS RM sources:
Conservative estimate for GALFACTS sources in this region: +2000!
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Key Observational Questions(ie. The Puzzles)
• ...the number and location of reversals?• ...the alignment of the field with the spiral arms?• ...what the disk-halo transition looks like?• ...what sort of cross-scale coupling exists?
Can we identify...
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Identifying Magnetic Field Reversals
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Thompson et al. 1980 Simard-Normandin & Kronberg 1980
A reversal in the Sagittarius arm is demonstrated.
Reversals in the Inner Galaxy
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Rand and Lyne 1994 Frick et al. 2001
Reversal assumed to continue into the Carina arm.
Reversals in the Inner Galaxy
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Interpreting the SGPS Data
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Interpreting the SGPS Data
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Important Lines-of-Sight
SGPS
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Important Lines-of-Sight
SGPS
Carina arm: ClockwiseCrux arm: Counter-Clockwise
IN Q4:
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Important Lines-of-Sight
IN Q4:Carina arm: ClockwiseCrux arm: Counter-
ClockwiseSGPS
IN Q1 (expect):local arm: Clockwise
Sagittarius arm:Counter-Clockwise
GALFACTS
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Important Lines-of-Sight
IN Q4:
GALFACTS
Carina arm: ClockwiseCrux arm: Counter-Clockwise
SGPS
local arm: ClockwiseSagittarius arm:Counter-
Clockwise
IN Q1 (expect):
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Field Alignment with the Spiral Arms
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Field Alignment: Recent Proposals
Weisberg et al. 2004 Han et al. 2006
Field is assumed to follow the spiral arms,consistent with external galaxy observations.
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Vallee (2005) proposed a circular field model.
Field Alignment: Recent Proposals
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Predicted RM Nulls
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New High-Longitude CGPS RMs
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New High-Longitude CGPS RMs
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CGPSGALFACTS
Overlap
Detecting the RM Null
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CGPSGALFACTS
Overlap
Both CGPS and GALFACTS will detect the Null... ...but GALFACTS will solidify the location.
Detecting the RM Null
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Available Data in the Fourth Quadrant
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Available Data in the Fourth Quadrant
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Available Data in the First Quadrant
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Available Data in the First Quadrant
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Symmetry Between Q1 and Q4?
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Symmetry Between Q1 and Q4?
CGPS might detectRM transition...
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Symmetry Between Q1 and Q4?
GALFACTS will
detect RM transition.
CGPS might detectRM transition...
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Halo Field & Disk-Halo Transition
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Vertical Symmetry and Reconnection
Quadrupolar (even symmetry)
“Dipolar” (odd symmetry)
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High Latitude CGPS Region in RM
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Exploring Regions out of the Disk
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Cross-Scale Coupling
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Scale Sizes of the Magnetic Field
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Scale Sizes of the Magnetic Field
= +
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Isotropy of the Random Field
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Correlation between |RM| and σRM
From analysis of CGPS data
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Anisotropy of the Random Field
• What is (are) the source(s) of the perturbations?
• How does the large-scale field couple to the small-scale field?
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Anisotropy of the Random Field
• What is (are) the source(s) of the perturbations?
• How does the large-scale field couple to the small-scale field?
The expected source density from Arecibowill allow better probing of these questions.
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•The complete geometry of the Galactic Magnetic Field is far from being conclusively determined.
•Unanswered Questions:• How many reversals are in the inner Galaxy?
• What is the field alignment w.r.t. the spiral arms?
• What is the halo field geometry?
• How does the field transition from the disk to halo?
• How does cross-scale coupling occur?
•Obtaining answers requires Arecibo.
Summary(Things to walk away with...)
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We’re not done yet...
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We’re not done yet...
...but we’re getting closer!