3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry Opportunities for Dust Polarization Surveys C. Darren Dowell (Caltech) 1/30

Outline magnetic fields in interstellar clouds observational and theoretical approaches dust composition, shape, and alignment sensitivity comparison survey approaches 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry2/30

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry3/30 Magnetic Field Strengths in Interstellar Clouds

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry4/30 Galactic Field in A V ≈ 1 Medium optical polarimetry

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry5/30 Galactic Field in A V ≈ 10 Medium BICEP: southern sky at = 2 mm, 1º resolution

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry6/30 Galactic Field in A V ≈ 100 Medium FIR-bright cloud cores: no B angle correlation with Gal. plane data from Dotson et al. (2000, 2008)

Measuring Magnetic Fields In addition to the usual problems with line-of-sight averaging and unresolved structure: vector B = (B x, B y, B los ) –B los : Zeeman, Faraday rotation –tan -1 (B y /B x ): synchrotron, dust polarization 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry7/30

Measuring Magnetic Fields In addition to the usual problems with line-of-sight averaging and unresolved structure: vector B = (B x, B y, B los ) –B los : Zeeman, Faraday rotation –tan -1 (B y /B x ): synchrotron, dust polarization –√(B x 2 +B y 2 ): dust polarization via Chandrasekhar-Fermi approach? 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry8/30

WMAP all-sky synchrotron map 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry9/30

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry10/30 Berkhuijsen (1997)

complementarity of synchrotron and dust mapping 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry11/30 Blue: Spitzer 8  m red: Bolocam/CSO 1.1 mm purple: VLA 20 cm Bally et al. (2009)

complementarity of synchrotron and dust polarization 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry12/30 Chuss et al. (2003)  m

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry13/30 Far-IR polarimetry is an excellent tracer of magnetic fields at densities up to 10 6 cm -3. Schleuning (1998) Rao et al. (1998)Ward-Thompson et al. (2000) Orion Core L183 Dark Cloud B vec

Tests of Cloud and Core Formation Theory with FIR Polarimetry Ordered structures –flow along field lines –tidal shear –swept-up shells –accretion disks Large features resulting from instabilities Dispersion in field –Chandrasekhar-Fermi approach 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry14/30

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry15/30 Far-IR polarimetry tests geometrical models of magnetic fields: protostars “hourglass” field in protostellar envelope NGC 1333 IRAS 4A observation w/ interferometer: Girart, Rao, & Marrone (2000) model: Fiedler & Mouschovias 1993 B vec

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry16/30 Far-IR polarimetry tests geometrical models of magnetic fields: cloud cores Kirby (2008) Schleuning (1998); Houde et al. (2004)

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry17/30 Kim & Ostriker (2006) swing amplifier effect magneto-Jeans instability Kim & Ostriker (2001) Far-IR polarimetry tests geometrical models of magnetic fields: cloud formation

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry18/30 Magnetic Field Strength from Chandrasekhar-Fermi Method B = x  1/2  v /  x: Ostriker et al.(2001); Padoan et al. (2001); Heitsch et al. (2001); Falceta-Goncalves et al. (2008) strong field: small dispersionweak field: large dispersion Falceta-Gonçalves, et al. (2008)

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry19/30 Magnetic Field Strength from Chandrasekhar-Fermi Method B = x  1/2  v /  x: Ostriker et al.(2001); Padoan et al. (2001); Heitsch et al. (2001); Falceta-Goncalves et al. (2008) strong field: small dispersionweak field: large dispersion Falceta-Gonçalves, et al. (2008) B  80  G

Grain Alignment & Composition current theory of grain alignment (Lazarian et al.): –Paramagnetic relaxation no longer needed. –Instead, radiative torques on asymmetric grains will do. –Alignment with polarization perpendicular to field still applies. Observational tests possible. 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry20/30 Vaillancourt et al. (2008)

Into the Next Decade optical/near-IR: big surveys of starlight polarization FIR: –BLASTpol: mapping full molecular clouds –SOFIA: precision application of Chandrasekhar-Fermi submm: –Planck: all-sky polarization survey –ALMA: great for circumstellar dust? radio: EVLA, GBT 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry21/30

HAWCpol/SOFIA 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry22/30 observation bands 53, 89, 155, 216  m angular resolution5 – 22 arcsec field of view0.5×1.2 – 1.6×4.3 arcmin 2 polarization modulation techniquequartz half-wave plate, 15 rpm minimum flux density to achieve  (P) = 0.2% in 5 hour integration 9, 6, 6, 5 Jy minimum column density to achieve  (P) = 0.2% in 5 hour integration A V = 1, 2, 5, 4 systematic error goal  P < 0.2%;  < 2° started Oct on JPL internal funds permanent upgrade to HAWC good for sources up to ~8’

Required Polarization Sensitivity typical degree polarization = 3% typical intrinsic dispersion = 10° – 30°   (  ) = 3°,  (P) = 0.3%  photometric signal-to-noise of 500 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry23/30 Hildebrand et al. (1999)

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry24/30 Far-IR polarimetry is 10 6  faster from space. sensitivity to extended emission BLASTpol

Giant Steps MIDEX-class FIR polarization survey SAFIR polarimeter SPIRIT polarimeter EPIC (CMBPol) with extended high- frequency coverage SKA 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry25/30

Dedicated Polarization Survey 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry26/30 PIREX/M4 (Clemens, P.I.; Goodman; Jones) –satellite proposed to NASA 1990, 1993, 1996 –possible reasons for non-selection: Polarimetry not a scientific priority for NASA. Difficult for a cryogenic mission to compete on the NASA SMEX playing field. Unsuccessful Origins Probe proposal to study FIR polarimeter and C + heterodyne spectrometer on 0.5 – 1 m telescope (Dowell, Langer et al.) M4: 0.2 m cold telescope

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry27/30 with SAFIR/CALISTO: 5 hours integration time (10 4 detectors) 5” = 20 pc resolution at = 100  m likely detection of polarization wherever A V > 0.3 MIPS 24  m (Gordon et al.)

EPIC Polarization Mapping EPIC/850 GHz can make accurate polarization maps with 10 8 resolution elements. coverage map,  (P) ≤ 0.3% Planck/350GHz 5’ EPIC/850GHz 40K, 5’ EPIC/850GHz 4K, 1’ 3/11/0928 C. D. Dowell, Keck Institute/Dust Polarimetry

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry29/30 Enabling Technologies for Space Far-IR Polarimetry polarization-sensitive detectors polarization modulation –low-power cryogenic rotating quartz half-wave plate –scan modulation only (Boomerang  Planck) Good polarimeters usually make good cameras. –NEP = W Hz -1/2 is adequate for detectors.

Antenna-Coupled 200  m TES Detector 3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry30/30 work by Peter Day et al. (JPL/Caltech)

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry31/30 “If nuclear and gravitational forces were the only forces at work in the universe, the broad pattern of cosmic evolution would be one of gradual thermal degradation punctuated by occasional explosive events. The cosmos would resemble the serene and monotonous heavens of classical conception. There is, however, a cosmic agitator: the magnetic field. Although only a small part of the available energy in the universe is invested in magnetic fields, they are responsible for most of the continual violent activity of the cosmos, from auroral displays in the earth's atmosphere to stellar flares and X-ray emission, and the massing of clouds of interstellar gas in galaxies.” E. Parker, Scientific American (1983)

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry33/22 Theory and modeling will play an important role in interpretation of polarimetry. MHD simulations to get factors of order unity in application of Chandrasekhar-Fermi method magnetic field models of specific structures –forming molecular clouds –collapsing cores: magnetic regulation, magnetic braking –circumstellar disks and envelopes –accretion into Galactic center dust grain alignment theory to understand environmental effects on and wavelength dependence of polarization

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry34/22 Polarization Power Spectrum: Probe of Turbulence

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry35/22 Magnetic Field Strengths in Interstellar Clouds Crutcher (2008) strong field weak field

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry36/22 Polarization Power Spectrum: Probe of Turbulence Some expectation of steepening of spectrum at ambipolar diffusion length scale  pc  1” in Orion (Li & Houde 2008)

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry37/22 Magnetic fields and IR astrophysics large-scale gas flows in galaxies timescale of cloud and star formation shapes of clouds turbulence disk, wind, jet, and shock physics

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry38/22 Multi-Wavelength Imaging and Polarimetry warm and cold components in Galactic center circumnuclear ring Vaillancourt et al. (2008) continuum polarization spectrum normalized to 350  m 32  m450  m Latvakoski et al. (1999)

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry39/22 B pos vs. elongation angle in cloud cores Tassis et al. (2008) roundelongated data from Dotson et al. (2000, 2008)

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry40/22 Space far-IR polarimetry with a 5+ m telescope is an essential tool. Consider a modest instrument on a 5 m telescope cooled to 4 K (‘CALISTO’): –1000 polarization-sensitive pixels covering bands at =  m (most of the mass and luminosity, component separation) –angular resolution 5˝ at 100  m (protostellar size scale) CALISTO: design concept for SAFIR

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry41/22 Prospects for space far-IR polarimetry Infrared Space Observatory ( ): polarimeter add-on, limited results M4: not funded Spitzer Space Telescope ( ): no polarimetry Herschel Space Obs. ( ): no polarimetry Planck ( ): all-sky survey, 300˝ resolution SPICA ( ): no polarimetry planned 2001 Decadal Survey: –“Magnetic fields play a crucial role in … the formation of stars….” –“Polarization” only mentioned in context of CMB. Much the same story in NASA science plans. Conclusion: Need to start campaigning early for a polarimeter on a big, cold telescope.

3/11/09C. D. Dowell, Keck Institute/Dust Polarimetry42/22 Wide Polarization Survey from Space Map 100 square degrees worth of molecular clouds at = 100  m (5˝ resolution with 5 m telescope): –Detect polarization where A V ≥ 0.3 –Requires 50 hours with 10,000 pixel detector array Contours show regions where  (P) would be < 0.3%. Millions of polarization vectors  map of magnetic field structure and strength on almost all relevant angular scales. Orion A Orion B  Oph 10º