1. POL-2 Polarimetry for the JCMT in the EAO era Antonio Chrysostomou, Pierre Bastien and the POL-2 Team

2. POL-2 Commissioning Team P. Bastien, A. Chrysostomou, D. Berry, D. Johnstone, P. Friberg, G. Savini, S. Coudé, M. Houde, J. Greaves

3. POL-2: a Polarimeter for SCUBA-2

4. Overview o Quick update from commissioning o A science case for a POL-2 survey o Magnetic fields in molecular clouds o Dust grain physics o More for discussion at this meeting o Conclusions

5. POL-2 installation at JCMT July 2010 ‘Blade’ housing containing the spinning waveplate, analyser and calibrating wire-grid polarisers

6. Commissioning Update o On-sky commissioning: March-September 2013 o Demonstrated that the instrument works and functions as a polarimeter, although some issues revealed o cross-talk between harmonics (under control, we think we understand this) o instrumental polarisation (IP) needs to be better understood o a simple model (based on the membrane) yields good fit to planetary data but there is strong scatter present o telescope IP component is expected to vary across the focal plane o stability of SCUBA-2 detectors… o Basic observing mode (stare & spin) works, others not tested o Data reduction works – can make maps and remove IP (once we understand it!)

7. Mars IP measurement Systematic errors introduce a sensitivity floor

8. OMC-1 Commissioning Data SCUBA pol. Matthews et al. (2009)

9. Survey options for POL-2 o What is the science case for a POL-2 survey? o here I choose the two obvious cases o Mapping of magnetic fields o characterisation of magnetised turbulence in molecular clouds and star forming regions o the role of filamentary structure o Dust grain physics o testing grain alignment mechanisms

10. Submm Polarimetry o Multi-scale mapping of magnetic fields o Geometry of fields in POS, in 3D o Characterization of magnetized turbulence in molecular clouds and star forming regions o Dust grain physics o Testing grain alignment mechanisms o Polarisation spectrum NEW

11. Mapping magnetic fields o Polarisation → geometry of the field in plane of the sky (POS) o Can obtain 3D maps of the magnetic field by including spectral information (Houde et al. 2002): o Dust polarimetry → B in POS o Zeeman splitting of spectral lines → strength of B along l-o-s o Ion-to-neutral molecular line-width ratio angle between B and l-o-s (Houde et al. 2000)

12. The orientation of the projection of the magnetic field in the POS is shown by the vectors. The viewing angle is given by the length of the vectors (using the scale shown in the bottom right corner). Contours & gray scale: total continuum flux. Houde et al. 2002 CSO & Hertz, 350 µm

13. Mapping magnetic fields o Characterisation of magnetised turbulence in molecular clouds and star forming regions Context: need to hold up clouds & prevent rapid collapse (otherwise SF efficiency is too high) o Both turbulence and magnetic fields are invoked o Can differentiate contribution from each by calculating the angular dispersion to evaluate contributions of turbulent and ordered field components (Hildebrand et al. 2009, Houde et al. 2009)

14. Mapping magnetic fields o The angular dispersion method allows determination of (Houde et al. 2009): o turbulent correlation length o turbulent/ordered field energy ratio o plane of the sky ordered field strength o turbulent power spectrum

15. SCUBAPOL polarisation map @ 850 µm OMC-2 & OMC-3 Angular dispersion function: Angular dispersions vs. distance, displacement between pairs of magnetic field vectors → dispersion about large- scale fields Poidevin et al. (2010) Higher turbulent component

16. OMC-1 / SHARP - Results16 Houde et al. 2009, ApJ, 706, 1504

17. OMC-1 with SHARP at 350 µm17 beam Houde et al. 2009, ApJ, 706, 1504

18. Mapping magnetic fields o Herschel has shown us that filaments appear to be ubiquitous in SF regions Pipe Nebula, (Peretto et al. 2012, A&A, 541, A63)

19. Andre et al 2013 (arXiv1312.6232) PPVI in press Lupus I with BLASTpol Matthews et al 2014, ApJ, 784, 116 Palmeirim et al. 2013 A&A 550, A38

20. Orion A North, Salji et al. 2014 DR21/Cygnus, Natario et al. in prep.

21. Dust grain physics o Grain alignment theories: o Mechanical (Gold 1952) ‒ NO, too weak o Paramagnetic relaxation (Davis & Greenstein 1951) & enhancements (e.g., Purcell 1979; ferromagnetic, or suprathermal rotation) ‒ Difficult to reconcile with observations o Radiative torques (RT) (Dolginov & Mytrophanov 1976, …, Hoang & Lazarian 2008, 2009) ‒ Observational support: Whittet+2008; Andersson & Potter 2010 → in the NIR

22. Predictions of RT alignment Molecular cloud environmentAlignment? 1Cores with embedded YSOsYes, very efficient 2Cores without a protostar (or starless cores) Decreases with τ (or A V ) above a threshold o Grain alignment is sensitive to ratio (λ/ a ) o Reddening of external radiation field due to dust extinction removes short wavelength photons necessary to align smaller grains in grain size distribution. o With progressively fewer aligned grains, expect value of P/τ to drop o Whittet et al. (2008) found this adequate to explain their observations up to A V ~ 10 mag.

23. 2-comp. model with uniform + turbulent mag. field Whittet et al. (+) NIR data reaches to A V ~ 10 Jones et al. (2014, subm.) Starless cores (SCUBA- pol) Matthews et al. (2009) K-band polarimetry Deep K-band polarimetry extends data to A V ~50, and seems to fit to Whittet model.

24. Submm data extends reach to A V = 100+ Model assumes degree of alignment decreases as a function of optical depth. Change in slope indicative of grain alignment weakening deeper into the molecular cloud when no protostar is present Jones et al. (2014, subm.)

25. Polarimetry in K-band Jones et al. (2014, subm.) +: Whittet et al. 2008 Filled symbols : Jones+2014 Curves: Pmax: equivalent to P max = 9.0 E(B-V) (Serkowski et al 1975) i.e., perfect alignment in plane of sky Whittet: fit to + data, slope, b = -0.52 ± 0.07 JKD: 2-component model with uniform & turbulent magnetic field components Up to A V = 48!

26. Comparison to submm data Starless core L183 SCUBAPOL data (Matthews et al 2009) only P/  P > 3 Notes: B (, T ) : blackbody function  : beam solid angle Jones et al. (2014, subm.)

27. Comparison to submm data Starless core L43 SCUBAPOL data (Matthews et al 2009) only P/  P > 3 Jones et al. (2014, subm.)

28. NIR and submm data Jones et al. (2014, subm.) Open triangles: L183 Open circles: L43 Submm data were shifted vertically to match NIR data (assumes grain population causing polarisation in extinction is same as grain population causing polarisation in emission) Model fit assumes alignment of grains decreases as a function of optical depth into the cloud

29. NIR and submm data Jones et al. (2014, subm.) Transition from slope of ~ -0.5 to ~ -1.0 at A V ~ 20; shows that grain alignment decreases going deeper into the clouds when no star is present Alves et al. (2014) also find P submm drops as  - 1.0 for starless core Pipe-109 in the Pipe nebula Poidevin et al. 2010 Region “South of FIR6” is quiescent, 26 vectors → slope P vs.  of -1.0 ± 0.4, consistent result

30. Dust grain physics (2): Polarisation spectra Vaillancourt, Andersson & Lazarian 2013 Observations Median polarisation ratio, normalized to 350  m. Schematic FIR spectra ~ 10 – 1000  m for a cloud with embedded stars Dotted lines: 2 regions with different aligning radiation fields Solid line: mean spectrum

31. Overview  Science case  Polarisation survey  Conclusions

32. Options for a polarimetry survey o Include best regions from existing JLS/Herschel surveys o Meet 2 major goals o mapping B-fields in SF regions o testing grain alignment mechanisms o Variety of SF regions to allow statistics o include regions with YSOs and starless cores, enough to do statistics Would require ~ 200 hours …?

33. Conclusions o Polarimetry with POL-2 offers opportunity to o improve our understanding of magnetic fields and turbulence in star-forming regions o tests grain alignment mechanisms o Best done with dedicated polarisation survey of modest scope, crafted to meet science goals

34. Thank you!

36. POL-2: a Polarimeter for SCUBA-2

37. POL-2 Teams  POL-2 instrument team  POL-2 Guaranteed-Time Team  POL-2 Team: P. Ade, S. Bernier, D. S. Berry, E. Bissonette, A. Chrysostomou, S. Coudé, P. Friberg, B. G. Gom, J. Greaves, W. Holland, M. Houde, T. Hezareh, D. Johnstone, T. Jenness, J.-T. Landry, M. Leclerc, B. C. Matthews, D. A. Naylor, G. Pisano, G. Savini, A. Simon

38. POL-2  Built with 2 grants from CFI/partners granted in 2002 and 2006 as part of the SCUBA-2 package  POL-2 delivered at JCMT: July 2010  Commissioning: September 2012 – on- going

39. SCUBA-2 Polarimeter  3 major requirements  Remove atmospheric effects: rotate HWP at 2 Hz  Possibility to calibrate on the telescope: calibrator  Polarimeter is available all the time: move components in & out of beam  3 optical components:  Achromatic half-wave plate (450 µm - 850 µm)  Wire grid polariser – analyzer  Wire grid polariser – calibrator

40. Half-wave plate transmission 850 450

41. SCUBA-2 Polarimeter  3 Operation modes:  STARE & spin (grid map)  SCAN & spin (to be tested)  Step & Integrate (no spinning; fall-back mode)

42. Data Acquisition & Observing Mode  Use standard observing tool (OT) and MSBs  Basic observing mode: stare at sky while spinning HWP at 2 Hz → polarisation modulation of 8 Hz in time series data from the bolometers (read at 200 Hz)  Use 5 x 5 grid pattern spaced by 1 ′ to fill holes due to dead bolometers and gaps between subarrays

43. Data Reduction  Time series data from each bolometer is flat fielded, cleaned & corrected for extinction  Multiply by sin & cos functions at expected modulation frequency to get Q & U images  Individual images combined  Stokes I image comes from separate scan observations before and/or after polarisation stare observations

44. Commissioning observations  September 2012, ≈ 4 half-nights, DR-21, OMC-1, IRAS 16293-2422, sky dips  February 2013, 2 half-nights, OMC-1, CB 54, sky dips  March 2013, sky dips  May & July 2013, planets  August 2013, planets, W48  September 2013, planets, Crab neb., sky dips

45. Sensitivity floor  Top: Uncertainties for Q, U and PI decrease as N -1/2 down to a sensitivity level of ~ 6 — 7 mJy as more data are coadded together. Dashed line: expected behaviour  Bottom:  Red: uncertainties of individual measurements  Blue: expected behaviour from these uncertainties  Note: sensitivity level reached depends on aperture size (here 40 ″ used)

46. Commissioning Update 1aObserving mode: Stare & spinOK (efficient for t ≥ 30 s) 1bObserving mode: Scan & spinTests needed 2Flat field correctionOK 3Sky subtractionOK 4aInstrumental pol. determination: membraneOK 4bInstrumental pol. determination: telescopeMore work needed 5Sensitivity floor (noise integration)Floor level still present 6Cross-talk between harmonicsUnder control 7Polarisation efficiencyOK 8Origin of position anglesOK Note: 5 depends (entirely?) on 4b

47. Many oblique reflections before reaching the detectors, giving rise to IP

49. Wire grid in front of the half-wave plate

50. Filament growth Palmeirim et al 2013 A&A 550, A38

51. Lupus I & III Rygl et al 2013 A&A 549, L1

52. Lupus 1 filament Blastpol B-field measurement Blue line traces filament Matthews et al 2014 arXiv1307.5853 ApJ accepted

53. Cores form on filaments Andre et al 2013 arXiv1312.6232 PPVI in press