Presentation on theme: "MAGNETIC FIELDS IN THE MILKY WAY AND BEYOND Carl Heiles, UC Berkeley."— Presentation transcript:
MAGNETIC FIELDS IN THE MILKY WAY AND BEYOND Carl Heiles, UC Berkeley
GALACTIC: ALFA’s combination of sensitivity and resolution reveals unanticipated structures: Shocks or intermittency in turbulence Small clouds raining onto the Galaxy Magnetic needles Blobs
Spatial structure in profile wings is NOT SMOOTH! Instead: High KE/mass Shocks? Intermittency in turbulence?
GALFA images of HI: ALIGNED FILAMENTS over wide velocities. Thin lines: starlight polarizations. Thick black line: vector average.
GALFA data of this 150 sq deg region: Vlsr = 5 to 12 km/s Note the long, straight filaments!
BASIC OBSERVED NEEDLE PROPERTIES: lengths up to ~5 degrees (~10 pc) width down to ~5 arcmin (unresolved?) (~0.1 pc) aspect ratios up to ~50 typical N(HI)~4 X 10 18 ~25 solar masses per degree (~5 suns per pc) strongly aligned with each other and with the local magnetic field
Numerical simulations: colliding streams form filamentary structures with magnetic fields along the axis. GALFA reveals this morphology. How about the STRENGH?
Here’s a typical needle profile. Very well defined. But weak! Reaching a 10 microGauss (3 sigma) requires integrating for about 160 hours. This is almost prohibitive until we look at the stronger cases and pick a few; then, in a few hundred hours, we can get good limits on a few samples and explore the situation.
HI BLOBS... Unresolved at Arecibo (dia < 4 arcmin) HI mass ~10 -3 Suns Molecules? Look for OH, H2CO, CO, etc. Magnetic fields? About 40 hours to reach 10 microGauss (3 sigma) in HI Zeeman splitting. Virial mass ~ 10 Suns. molecular protostar? HI stellar envelope? DARK MATTER? (Hoo boy...COSMOLOGY connection...that should impress those Senior Review Jokers)
There is a sense that field DIRECTIONS in the small, highly concentrated OH masers tend to mirror the LARGE-SCALE fields in the local vicinity. This realization arises from interpreting a LARGE-SCALE SURVEY OF GALACTIC OH MASERS LARGE-SCALE SURVEYS ARE ASTRONOMY’S BREAD AND BUTTER.
Minimum energy and equipartition suggest magnetic fields in ULIRGs should be between 1 mG to 10 mG (Thompson et al. 2006) ULIRGs (L FIR /L >10 12 ) are powered by starbursts or AGN. OH megamasers (L OH /L =10 1-4 ) are found in ULIRGs (Darling & Giovanelli). Magnetic Fields in ULIRGS Arp 220 Thompson, Rieke, Schneider, Scoville, & NASA NASA, ESA, & C. Wilson
Pihlström, Conway, Booth, Diamond, & Polatidis 2001 100 pc
III Zw 35 +3mG-3mG As for the Milky Way, OHMMs probably trace LARGE-SCALE FIELDS. Often (as here) the SIGN of B REVERSES ACROSS THE PROFILE. This suggests a TOROIDAL FIELD-- JUST LIKE THE MORPHOLOGY AND KINEMATICS.
WE NEED VLBA MAPS to pin this down! V spectra are weak...we need the High-Sensitivity VLBA (the HSA, which includes all VLBA dishes, all VLA dishes, GBT, and Arecibo). We need at least 0.3 mJy 1-sigma sensitivity in the OH line and good UV coverage. A single 12-hour track with the full HSA will just do the trick. HOW MANY SOURCES? Start with a few good cases and see what happens...
HOW DO WE GET THESE “few good cases’’ for VLB mapping? We begin with a COMPLETE SURVEY of OHMMs for Zeeman splitting. Only ARECIBO has the useful sensitivity. We proposed (455 hours). One referee’s response:
“...Normally, I would recommend that this proposal be scheduled as soon as possible and be alloted 100% of the requested time...The only concern has to do...with...the recent decisions by the NSF...I’m reminded of a line from the 2 nd Lord of the Rings movie: ‘How did it all come to this...?’ ’’
OK...I’ll be a good boy, back to science... Yesterday Jeremey told us about OH absorption and conjugate lines. Yesterday, Jeremey told us about absorption and conjugate OH lines in ULIRGs. And: at z=1, we expect 1 OHMM per square degree! We can measure Zeeman splitting for all these and compare field strengths in/outside masers; and look at fields in the HIGH-Z beginnings of binary black holes from merging galaxies!
We need to begin pilot observations ASAP to assess feasibility. Observing significant numbers of High-z OHMM OH absorption/conjugate lines, are large, time-intensive projects.
GLOBAL SUMMARY: GALACTIC: Our GALFA survey reveals new ISM phenomenae. EXTRAGALACTIC: We have discovered OHMM Zeeman splitting—the only direct measurement of extragalactic fields. WE NEED LOTS OF FOLLOWUP OBSERVATIONS WITH ARECIBO and the VLBA
At 40 km/s, the distance is a few kpc. These blobs and filaments are raindrops condensed from the warm halo gas. Do they carry magnetic fields?
The NSF: “Once you’ve mapped the HI sky, you’re all done—you can throw away the spectrometer and the telescope.’’ REALLY? Followup: Magnetic field Molecular mapping (OH, H 2 CO, CO,...) Higher sensitivity (for HVCs) Let’s look at some of these “unanticipated structures’’
Arp 220 Rovilos, Diamond, Lonsdale 2, & Smith 2003 0.25"0.5" 1.5" = 550 pc
We detect OHMM magnetic fields in MOST of the ULIRGS we observed. The OHMM fields probably trace the LARGE- SCALE FIELDS in these colliding systems. Often, the SIGN of B REVERSES ACROSS THE PROFILE—suggests a TOROIDAL FIELD in the rotating disk/torus. We need VLBA MAPS to pin this down!