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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Last modified 08 December 1999