OH MASERSin

THE MILKY WAYand

BEYOND

There is a sense that field DIRECTIONS in the small, highly concentrated OH masers tend to mirror the LARGE-SCALE field directions in the local vicinity.

OH masers are associated with HII regions, whose distances are known. Moreover, OH masers are BRIGHT.

OH MASERS UNIQUELY OFFER LOCAL FIELD DIRECTIONS THROUGHOUT THE GALAXY

The Discovery of Extragalactic Magnetic Fields

in OH Megamasers

Tim RobishawCarl HeilesEliot Quataert Berkeley

• Minimum energy and equipartition suggest magnetic fields in ULIRGs should be between 1 mG to 10 mG (Thompson et al. 2006)

The Story

• Minimum energy and equipartition suggest magnetic fields in ULIRGs should be between 1 mG to 10 mG (Thompson et al. 2006)

• ULIRGs (LFIR/L>1012) are powered by starbursts or AGN.

The Story

Arp 220

• Minimum energy and equipartition suggest magnetic fields in ULIRGs should be between 1 mG to 10 mG (Thompson et al. 2006)

• ULIRGs (LFIR/L>1012) are powered by starbursts or AGN.

• OH megamasers (LOH/L=101-4) are found in ULIRGs (Darling & Giovanelli).

The Story

Arp 220

• Minimum energy and equipartition suggest magnetic fields in ULIRGs should be between 1 mG to 10 mG (Thompson et al. 2006)

• ULIRGs (LFIR/L>1012) are powered by starbursts or AGN.

• OH megamasers (LOH/L=101-4) are found in ULIRGs (Darling & Giovanelli).

• In the Milky Way, OH masers probe magnetic fields in star formation regions.

• Went to Arecibo to observe the 6 brightest OHMs, including the archetypal ULIRG Arp 220, in hopes of measuring Zeeman splitting in the 1667 MHz line.

The Story

Arp 220 III Zw 35

Arp 220

Rovilos, Diamond,Lonsdale2, & Smith

2003

0.25" 0.5"

1.5" = 550 pc

III Zw 35

Pihlström, Conway, Booth, Diamond,

& Polatidis2001

100 pc

Arp 220 III Zw 35

Arp 220 III Zw 35

+3mG -3mG

Gigamaser!

LOH/L>104

Pihlström, Baan,

Darling, & Klöckner

2005

Yu2005

200 pc

Gigamaser!

LOH/L>104

Gigamaser!

Reversal 18 mG!

LOH/L>104

• Detected 15 B fields.

• Detected fields in 4/6 ULIRGs.

• First extragalactic Zeeman splitting detections in emission lines.– Only previous extragalactic Zeeman detection was HI in absorption in

high-velocity cloud around Perseus A (Kazes et al. 1991; Sarma et al. 2005).

• B is similar to local sites of OH masers.– Conditions in regions of massive star formation are similar to those in

Milky Way.

• B is consistent with inferred synchrotron fields.– Probing gas closer to typical

• Fascinating other issues:– B versus density

– Linear polarization – thorny interpretive issues

Results

More Data

• GBT survey of 7 ULIRGs awaiting reduction

• Arecibo survey continues this spring withthe 6 next-brightest OHMs

• High-sensitivity VLBA observations of Arp 220 and

III Zw 35

MAYBE YOU’VE NOTICED... (or maybe you don’t care...)

All radio data in this talk used the just-pictured telescopes--Arecibo (the most sensitive in the world by a factor 3) and the VLBA (its angular resolution makes HST look sick)--which were recently bludgeoned to death by NSF’s

SENIOR REVIEW COMMITEE

¡¡¡THANKS, GUYS!!!

SUMMARY

Field affected by gas morphology—and vice-versa

In CNM, morphology is primarily sheets/filaments.

In CNM, PB Pturb 3 Pthermal

In CNM/WNM, field larger in “filaments”

Galactic OH maser fields trace local large-scale field—only yesterday (Han/Zhang 2007) have we used this info!

Extragalactic OH megamasers offer a unique probe into large-scale fields in ULIRGS.