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 ~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.
GALFA FINDS HI BLOBS
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)
EXTRAGALACTIC: OH MEGAMASERS and ULIRGs
But First, a lesson from the Milky Way...
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 = ) are found in ULIRGs (Darling & Giovanelli). Magnetic Fields in ULIRGS Arp 220 Thompson, Rieke, Schneider, Scoville, & NASA NASA, ESA, & C. Wilson
Arp 220III Zw 35
Pihlström, Conway, Booth, Diamond, & Polatidis 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
THE END of THIS TALK
THE END of THIS KIND OF RESEARCH?
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’’
GALFA HI STRUCTURES WHAT NEXT WHAT NEXT?
Arp 220 Rovilos, Diamond, Lonsdale 2, & Smith "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!