Magnetic field structure
in star-forming regions
by polarization observations
Munetake MOMOSE (Ibaraki University)

Summary of this talk
• 星・惑星形成における磁場が果たす役割の解明は観測的に未開拓かつ重要テーマの１つ• 星・円盤形成時の磁場の役割やダスト整列に関し，予言能力・検証可能な理論が登場したことに加え，近年の観測進展（SCUPOL, PLANCK, ALMA）• 地上サブミリ波望遠鏡は，コア構造を分解(≲ 10”)しつながら高感度な広域観測が可能で，このテーマにとってユニークな装置能力を持たせうる

Introduction:
Star-formation & magnetic fields

Formation of low-mass stars

Importance of magnetic (B-)field information of stars and planets• Transportation of angular momentum in a core
• inevitable during star formation (∵ Lcore/Mcore ≫ L*/M*)• magnetic breaking catastrophe !?
• outflows & jets

• Turbulence by MRI in a disk
• provide viscosity in an accretion disk
• hinder the growth of dust grains• Dissipation of B-field should occur during star formation(∵ BcoreRcore2 ≫B*R*2); when, where and how ?

• Ambipolar diffusion → Ohmic dissipation in a disk ?
• Reconnection diffusion in a core ? (González-Casanova+ 2016)

Observational studies on B-field• B-strength: Zeeman effect, (Faraday rotation)• OH, CN, (HI)• CCS with large SDs and ALMA, mainly at 40 GHz• B-direction: Polarization due to dust extinction/emission• Polarization seen in background stars at optical & near-IR(extinction; B ‖ E-vector): mainly on large scales (> 1pc)
• Polarization in emission at far-IR & sub-mm (B ⟂ E-vector) :various size scales (shown later)• Millimeter & sub-millimeter wavelengths are unique :• B-field in densest & coldest regions• Ground-based telescope → high resolution + wide fieldDavis-Greenstein mechanism:--- a “classical” theory (1951) ---(paramagnetic)

B ∦ M (or H) due todelayed induction↓Torque↓Ωgr B

Dust alignment !?
What is the origin ofa fast (suprathermal)
spinning velocity ?

Induction of M in aspinning grain

Induction of M by
time-variable B

Radiative torques + grain “helicity”

Figures by Draine & Weingartner (1996); Andersson+ (2015) for the review

Polarization images:
extinction vs. emission

Polarization(l,b) map byextinction(optical & nIR)B ‖ pol. E-vector

Hall & Mikesell (1949)

Whittet (2003)

APdPolarization(l,b) map byemission at353GHz
pFig. 21. Dust polarization amplituderesolution of 100, produced by the0 map, P = Q2 + U 2, at 35320GHz, smoothed to an angular 200
di↵use component separation process described in (PlanckCollaboration
X2015)
using
PlanckandW MAP data.
µK@ 353 GHzPlanck Collaboration(2015)

B ⟂ pol. E-vector

Total intensity &Fig. 21. Dust polarization amplitude map, P = Q + U , at 353 GHz, smoothed to an angular resolutionof 10 , producedby theB-field
directiondi↵use component separation process described in (Planck Collaboration X 2015) using Planck and W M AP data.
RJp220Pol-images
in densecoresPolarization at mm-submm
in star-forming regions

SCUBA-POL at λ=850μm(Results in 1997-2005 by
Matthews+, ApJS, 182, 2009)
ρ-OphNGC1333

SCUBA-POL at λ=850μm(Results in 1997-2005 by
Matthews+, ApJS, 182, 2009)
OMC-1

83 SF-regions,
AGB stars, SNRs, …
GC

Star formation occurs in a filament--- Herschel studies --Herschel/SPIRE
250μm dust continuum image of
B211/B213/L1495 in Taurus(Palmeirim+ 2013)&“Fibers” in the filament
identified in C18O(J=1-0)(Hacor+ 2013)“Striations” ⟂ filaments, consisting of“fibers”

Comparisons with B-field from near-IR
Green: B-field suggested by
dust polarization in near IR(Heyer+ 2008; Chapman+ 2011)Black: Filaments
Blue: Striations
Star-forming Filaments(figure from PPVI, Andre+ 2014)

Dust polarization seen by ALMA (1):--- massive SF clumps (Cortes+ 2016) --0.56

W43-MM1 (d=5.5kpc)

0.48
◦′′′

− 1 54 24.0Dec (J2000)

27.0′′

0.40

0.32

0.2430.0′′

0.16

0.08

33.0′′

36.0′′47.40s

Flux (Jy/beam )3” ≈0.08pcA fragmented filament,
containing ~ 15 clumps(14- 312M⦿)
B strength in clumps
0.2-9 mG, estimated fromΔv(C18O), n(H2) & δφ

0.00
47.20s47.00s

46.80sRA (J2000)

46.60s46.40s18h 47m 46.20s

Color + contour image : Stokes I at λ=1mm;
pseudo-vectors: B-fields (blue > 5σ; green > 3σ)

g. 2.— The Figure shows the magnetic ﬁeld morphology over W43-MM1. The Stokes I emission is shown
color scale, the dust, rician debiased, polarized intensity is shown in contours of 0.55, 1.3, 2.0, 2.7, and5 mJy beam−1 . The magnetic ﬁeld morphology is shows as pseudo-vectors at a signiﬁcance of 3σ in green−1(Chandrasekhar & Fermimethod)

Dust polarization seen by ALMA (2):--- a protoplanetary disk (Kataoka+ 2016) ---100 AU

Stokes I at λ=0.9mm;

100 AU

PI & E-vectors ( > 3σ) by pseudo-vectors

Dust polarization seen by ALMA (2):--- a protoplanetary disk (Kataoka+ 2016) --HD142527 (d=140 pc)“Polarization flip” in NE, due
to self-scattering by large(size ~ 150μm) grains ?
(see also Kataoka+ 2015)
Radiative grain alignment ismore efficient than B-field ?
(Tazaki, Lazarian & Nomura2017)

100 AU

PI & E-vectors ( > 3σ) by pseudo-vectors

Summary of the current status• Large scale (> 1pc) B-fields and corresponding filaments• ALMA is accumulating new Pol. Data at smaller scale• Pol. does not always trace B-fields in protoplanetary disks• Good laboratories for studies on alignment mechanism• Progress in theories of dust alignment mechanisms• “Quantitative” predictive power• Connection btw large-scale and cores/clumps; unknown• BISTRO with JCMT/SCUPOL 2 ?
• Wide-field imaging with ≲ 10” resolution is essential• ALMA will not be the best instrument for this purpose …
(probably)Technical considerations

Draine (2003)

orWeingartner & Draine (2001) modelfor our Milky-way galaxy

Targets• Any frequency will do (350 GHz & > 800 GHz ?)• Av≳20mag., or N(H) ≳ 3.7×1022 cm-2 & cold (T ≈ 15K)
regions (see Draine (2003); to be complimentary to nIR andSPICA)• Polarization degree ≳ 5% (1σ = 1% of total intensity)• Systematic errors, loss in optics (e.g., transparency of HWP) &depolarization in the beam are for further studies• Advantage: Very stable condition in polar nights !?

• Suppressing other systematics• Differential imaging (frequent pol. switching) will be the key (c.f.
Subaru HiCIAO)• Status of BISTRO with JCMT/SCUBA2-POL ?

Av > 20mag, T=15K, 5%-pol.deg (5σ)
D=10m

D=30m

Frequency[GHz]

Beamsize [asec]

Required
Beamsize [asec]
Requiredsensitivity of 1%
sensitivity of 1%
Total I (1σ)
Total I (1σ)[mJy/beam][mJy/beam]

400

18.6

1.11

6.2

0.123

850

8.7

1.95

2.90.216※ 観測時間の見積もりは，(1)偏光成分取得，(2)半波長板透過率などの考慮もさらに必要。

Summary of this talk
• 星・惑星形成における磁場が果たす役割の解明は観測的に未開拓かつ重要テーマの１つ• 星・円盤形成時の磁場の役割やダスト整列に関し，予言能力・検証可能な理論が登場したことに加え，近年の観測進展（SCUPOL, PLANCK, ALMA）• 地上サブミリ波望遠鏡は，コア構造を分解(≲ 10”)しつながら高感度な広域観測が可能で，このテーマにとってユニークな装置能力を持たせうる