JCMT’s Next Generation of Polarimeters: POL-2 and ROVER Brenda Matthews (Herzberg Institute of Astrophysics)

Polarimetry Targets with SCUBA Range of target objects: Filaments, cores, galaxies, planetary nebula Non-exhaustive ADS search finds 28 refereed publications with 12 different first authors One consistent problem was the limited field of view “scan mapping” polarimetry for larger areas never produced robust results Difficulty in establishing the DC level of the background in the maps for I, Q and U Ratio of U/Q in calculation of polarization angle makes this critical 15 August 2006 Summer School "Submillimeter Observing Techniques"

Summer School "Submillimeter Observing Techniques" Crutcher et al. 2004 Matthews & Wilson 2002 Curran et al. 2004 Low Mass/Starless Star-forming Regions High Mass/Active Greaves et al. 2000 Greaves 2002 Planetary Nebula NGC 7027 Starburst Galaxy M82 15 August 2006 Summer School "Submillimeter Observing Techniques"

Outstanding Questions in Studies of Polarization of Interstellar Dust What is the role of magnetic fields (strength and geometry) before and during protostellar collapse? (very few cases studied) Are they the variable which regulates star formation? YES: Crutcher, Fiege, Stahler, MHD turbulence simulators NO: Elmegreen, Hartmann, MHD turbulence simulators… hmmm… What is the origin of the polarization holes? 15 August 2006 Summer School "Submillimeter Observing Techniques"

Summer School "Submillimeter Observing Techniques" POL-2: for SCUBA-2 Advantages over SCUPOL SCUBA-2’s higher sensitivity (3-5 x SCUBA at 850 micron) Larger FOV not all may be accessible to the polarimeter ~80-90%  diameter > 5.6 arcminutes (> 5x SCUBA FOV) Available all the time Removal of atmospheric effects to first order by rapid modulation of the waveplate 850 and 450 micron data should be well calibrated can use calibration polarizer 15 August 2006 Summer School "Submillimeter Observing Techniques"

Summer School "Submillimeter Observing Techniques" Area Larger field of view will greatly facilitate mapping of large and / or filamentary clouds which were a real challenge for SCUPOL. ? 15 August 2006 Summer School "Submillimeter Observing Techniques"

Summer School "Submillimeter Observing Techniques" Sky Noise Artefacts of Chopping Traditional “chopping” of the secondary mirror for a differential measurement will not be an issue with SCUBA-2. Rely on rapid waveplate modulation to remove sky noise (rotation speed 12.5 Hz) with detectors reading at 200 kHz, binned to 20 Hz. 15 August 2006 Summer School "Submillimeter Observing Techniques"

Summer School "Submillimeter Observing Techniques" POL-2: The Basics spinning fixed (reflecting half signal) 15 August 2006 Summer School "Submillimeter Observing Techniques"

Summer School "Submillimeter Observing Techniques" POL-2: The Basics Alignment of waveplate plane of polarization with analyzer Half-waveplate Orientation (degrees) Oscillating signal received by SCUBA-2 from a linearly polarized beam as the waveplate rotates 15 August 2006 Summer School "Submillimeter Observing Techniques"

Polarimeter Construction Ongoing at the University of Montreal (PI: Pierre Bastien) 15 August 2006 Summer School "Submillimeter Observing Techniques"

POL-2: Observing Example Source smaller than SCUBA-2 FOV 15 August 2006 Summer School "Submillimeter Observing Techniques"

POL-2: Observing Example sky Ip P% = 100 x (Imax-Imin)/(Imax+Imin) Total signal will consist of the Earth’s atmosphere emission (“sky”), unpolarized light from the source and a modulated signal due to the modulating polarized component. 15 August 2006 Summer School "Submillimeter Observing Techniques"

Calculating the Components Imin is unknown unless the sky level can be estimated Estimate from blank sky? Could also be estimated from a measurement without rotating the waveplate Imin = Iobs – (Ip at waveplate angle) Which observing mode is adopted will be critical 15 August 2006 Summer School "Submillimeter Observing Techniques"

So, How Fast Is It? (SCUPOL v. POL-2) 1 FOV to 5 mJy (1 sigma polarized rms) at 850 micron S x (P/100) -------------- S/N e.g. 1 Jy source polarized at 2%, requiring a S/N of 4 15 August 2006 Summer School "Submillimeter Observing Techniques"

So, How Fast Is It? (SCUPOL v. POL-2) 1 FOV to 5 mJy (1 sigma polarized rms) at 850 micron With SCUBA (jiggle/chop/nod) ~ 10 hours 15 August 2006 Summer School "Submillimeter Observing Techniques"

So, How Fast Is It? (SCUPOL v. POL-2) 1 FOV to 5 mJy (1 sigma polarized rms) at 850 micron With SCUBA (jiggle/chop/nod) ~ 10 hours With SCUBA-2* (no chop/nod) ~ 3 minutes ! Most known targets will be well detected with an rms of 0.6 mJy/beam (3.5 hours on source) likely the deepest polarimetry observation 15 August 2006 Summer School "Submillimeter Observing Techniques"

So, How Fast Is It? (SCUPOL v. POL-2) 1 FOV to 5 mJy (1 sigma polarized rms) at 850 micron With SCUBA (jiggle/chop) ~ 10 hours With SCUBA-2* (no chop/nod) ~ 3 minutes ! Statistically significant numbers of objects will be observable with POL-2 e.g. 100 cores in Gould Belt Survey to 1 mJy rms (126 hours) + 10 x 300 sq arcmin fields to 1 mJy rms (80 hours) 15 August 2006 Summer School "Submillimeter Observing Techniques"

Variable Polarization Targets e.g. Sag A* Flux density varies from 0.5-5 Jy and is typically polarized around the 10% level 50-500 mJy polarized intensity good angular measure  10 sigma Sag A* varies on timescales  20 min (Bower et al.) 850 m 450 Time interval Pol rms 3  1 minute 8.8 26.4 30 90 3 minutes 5.1 15.3 16 48 10 minutes 2.8 8.4 26.5` 20 minutes 2.0 6.0 6.2 18.6 15 August 2006 Summer School "Submillimeter Observing Techniques"

Summer School "Submillimeter Observing Techniques" POL-2 summary Allows for observations of many more objects than its predecessor Significantly deeper observations 450 micron observing likely to be common Faster speed means larger areas* and variable objects will be monitored easily over multiple epochs * Subject to constraints in mapping methods 15 August 2006 Summer School "Submillimeter Observing Techniques"

Polarization of Spectral Lines Goldreich-Kylafis Effect (Goldreich & Kylafis 1981, 1982; Kylafis 1983, 1983, 1983) Theoretical prediction of linear polarization of molecular lines Observationally confirmed in 1997 toward the evolved star IRC +10126 in CS 2-1 emission (Glenn et al. 1997) Linear polarization of pure rotational emission arises from molecules in the presence of a magnetic field due to imbalances in the magnetic sublevel populations 15 August 2006 Summer School "Submillimeter Observing Techniques"

Polarization of Spectral Lines Polarization levels are only around 1%, making detections very challenging Stronger in lower transitions Stronger in optically thin regimes Benefits are evident: Regions with different velocities are spectrally separated Quasi-3D picture of fields in rotating, outflowing or infalling gas is possible 15 August 2006 Summer School "Submillimeter Observing Techniques"

Polarization of Spectral Lines Promising technique to probe fields in outflows, cloud envelopes galaxies NGC 1333 IRAS 4A BIMA array Girart et al. (1999) 15 August 2006 Summer School "Submillimeter Observing Techniques"

ROVER (ROVing polarimetER) Polarimeter module completed and tested in March 2003 Tested at IRAM 30m in May 2003 Continuous spin timing accuracy at the millisecond level “world’s first imaging spectropolarimeter” 15 August 2006 Summer School "Submillimeter Observing Techniques"

Summer School "Submillimeter Observing Techniques" ROVER: for HARP-B 345 GHz range (e.g. CO 3-2 line) 12 of 16 HARP-B beams received without vignetting Design is similar to the SCUBA polarimeter Halfwave plate, analyzer More flexible motor and controller system for faster data rates Utilize new correlator, ACSIS, with its fastest sampling speed of 1/20th second 15 August 2006 Summer School "Submillimeter Observing Techniques"

ROVER & XPOL: SiO Maser R Leo 15 August 2006 Summer School "Submillimeter Observing Techniques"

Summer School "Submillimeter Observing Techniques" Timelines ROVER: already delivered to Hawaii Commissioning with HARP-B/ACSIS this fall (06B) POL-2: less definite 3-6 months after SCUBA-2 commissioning Expect earliest availability to users in Spring 2008 (08A) Required for ~200 hours of allocated time on the “Gould Belt Legacy Survey” 15 August 2006 Summer School "Submillimeter Observing Techniques"