Summary by M. Rupen.
Chaired by Frazer Owen
Also present:
Tim Bastian, Alan Bridle, Chris Carilli, Mark Claussen, Ketan Desai,
Vivek Dhawan, Jean Eilek, Chris Fassnacht, Dale Frail, Ken Kellerman,
Amy Mioduszewski, Rick Perley, Michael Rupen, Greg Taylor, Joan Wrobel
1- How to detect magnetic fields at radio wavelengths
a. We can derive three things: existence, orientation, strength
b. The methods
- Synchrotron and non-thermal radiation
- Rotation measures
- Anisotropic scattering
- Zeeman splitting
- Maser polarization
- Gyrosynchrotron emission
- Dust orientation at 7mm: use high-resolution to track dust alignment
Follow-up: Dale Frail
- Cyclotron lines (different frequencies correpsond to different plasma
layers --> 3D maps)
- Razin-Tsytovich
c. Background sources as probes
* We get lots of background sources:
at 20cm, about 127 suitable sources per 30amin beam, vs. perhaps
5-10 w/ current VLA
* Expansion Project offers
SENSITIVITY, for detectability
BANDWIDTH and SPECTRAL RESOLUTION, to track the pol'n
angle
POLARIMETRY at the same time, vs. now have to toss
channels
d. Zeeman splitting
* Not clear we win big.
* Would be nice to do Zeeman on ULIRGs, perhaps with A+.
* CHECK WITH TROLAND: are you ever limited by the instrument?
How about if we could give you time-stable D terms?
2- The Sun ***
Follow-up: Tim Bastian
Mostly covered by the 1995 workshop
* Three-dimensional tomography: use broad frequency coverage (up to 15 GHz)
to probe cyclotron emission at different depths
- can't do flares, since we can't change frequencies rapidly enough
* Map the heliosphsere using scattering and rotation measures (see solar
science working group)
3- Planets
Follow-up: Bryan Butler
see planetary science working group
4- Stars ***
Covered in the solar/stellar working group, under
"origins of stellar activity"
5- Pulsars
* Single-pulse polarimetry to get the geometry of the magnetic fields...
but GBT will do this
6- Stellar masers
* OH is too scattered for VLBA --> A+ mapping might be good
* sensitivity will help for 1720 MHz shock masers
Nothing stunning -- don't emphasize this
7- SNRs
* Masers in shocks
* RM, Faraday rotation probes
8- Galactic Center ***
9- Galactic molecular clouds ***
- detect mangnetic fields through Faraday rotation and statistical
depol'n
10- Pol'n of galactic background (as WSRT/de Bruyn)
12- Galaxies
* galaxy halos: 20 rads/m^2
* Spiral galaxies
* Map normal rather than special galaxies
* perhaps can also get to higher z???
* look for emission from "boring" galaxies -- e.g. dE -- are there mag.
fields?
13- Galaxy clusters ***
* Use background sources to probe the RM across a cluster
- many current RM probes are cluster members themselves, making it
difficult to disentangle RM from galaxy and from cluster
- typical RM= 0.8 Bparallel/microG n_e/cm^-3 l/pc
--> 10-20 rad/m^2
- Indications of extremely high RM
: Halpha; 3C295; cooling flows; etc.
--> figure out pressure support due to mag. field and how that affects
DM derivations
--> high-z magnetized clusters (.ps file)
--> where does magnetic field come from in cosmological objects?
* Cluster halos
- properties of halos vs. frequency: E Config. at high freq.
- fainter halos
- Uniform vs. filamented mag. fields --> sensitivity is paramount!
What happens on Mpc to kpc scales?
--> L or P band
14- Integalactic fields
* Faraday rotation vs. z
- can be done now, but you always win with more sources:
Bridle calls this a problem in pattern recognition, given the
spatial-frequency behavior of the Faraday rotation
- Art Wolfe claims excess Faraday rotation in damped Ly alpha absorbers
* Relationships along adjacent lines-of-sight: this goes as N^2, so you
win by a lot if you add more sources
- "Let confusion be your friend!"
- Find 3 quasars within 1arcmin of each other --> large-scale magnetized
structures in the early universe
15- High-redshift sources
* pol'n maps currently limited by resolution and sensitivity
* known source are all < 10asec; we want A+ at 1.4 GHz
* "We have a long history of misinterpreting pol'n at low resolution"
16- Lenses: RM of different images
* currently sensitivity limited
* CLASS lenses look spiral, not elliptical -- why do they have high RM?
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