November 24-25, 2016
The 6th DTA Symposium @NAOJ (Mitaka), Tokyo

Understanding the magnetic field structurein the star formation to the Galactic scales
through the maser observations
for Zeeman splitting and polarization
Sugiyama, Koichiro（Center for Astronomy, Ibaraki University）

Collaborators: Kenta Fujisawa; Yoshinori Yonekura

Table of contents
0. Brief introduction for masers
1. What’s advantages of maser observations for themagnetic field?
2. Remarkable works of maser observations for themagnetic field
3. Summary

0. Brief introduction for masers

Interstellar masersü Masers in the star-forming regions• Major : OH, H2O, CH3OH• Minor : NH3, H2CO, SiO, radio RL~200 Jy
G 023.01-00.41
1 km s-1

ü Characteristics• Much brighter than thermal lines"• Narrow line width : Δv ~0.2-0.5 km s-1"
• Compact size of spot : ~1-10 au "• Some spots consist of core/halo (Minier+ 02)☞ very bright : TB ~107-1012 K"
European VLBI spectrum and map of
the 6.7 GHz CH3OH maser (Bartkiewicz+ 16).

1,000 au

Usable characteristics of masersü Flux variability• Various times-scales: < 1 day – a few month – 1 year <• Provide information in 0.1-1 au spatial scales from Keplerian time-scale• Remarkable variation : Periodic, Flaring• Periodic : stellar pulsation / binary system ?
• Flaring : flare of exciting star / accretion burst / magnetic reconnection ?
30

Periodic

Flux Density [Jy]

20

15

10

1000

200 days

100

10

1

5

0

Flaring

50 daysLog flux density [Jy]Flux Density [Jy]

25

10000

1000 times!
57300

57350

0.1
57450
57500
57550
57600
57650
56600
56800
57000
57200
57400
Flux variation
monitorproject
resultswith
Ibaraki(Hitachi)single-dishradio
telescope.
MJD [day]
MJD [day]
57400

57600

Usable characteristics of masersü Flux variability• Various times-scales: < 1 day – a few month – 1 year <• Provide information in 0.1-1 au spatial scales from Keplerian time-scale• Remarkable variation : Periodic, Flaring• Periodic : stellar pulsation / binary system ?
• Flaring : flare of exciting star / accretion burst / magnetic reconnection ?

ü Proper motion with VLBI (a few milliarcsec (mas) spatial resolution)• Enable us to detect tiny motions of a few mas yr-1 on disk/outflow/jet• Reveal 3-D velocity structure with LSR velocity information

Proper motion with VLBI

Wide-angle outflow and jet scenario observed in high-mass SFR Cepheus A (Torrelles+ 11).
Proper motions of 22 GHz H2O masers showed expanding motions emanated by wide-angle
outflow, while a radio jet was observed by radio continuum observation.

Proper motion with VLBI

Expanding shell of bow shockpropagation

Shock propagation formed
by wide-angle outflow

2 mas
Wide-angle outflow and jet scenario observed in high-mass SFR Cepheus A (Torrelles+ 11).
Proper motions of 22 GHz H2O masers showed expanding motions emanated by wide-angle
outflow, while a radio jet was observed by radio continuum observation.

Usable characteristics of masersü Flux variability• Various times-scales: < 1 day – a few month – 1 year <• Provide information in 0.1-1 au spatial scales from Keplerian time-scale• Remarkable variation : Periodic, Flaring• Periodic : stellar pulsation / binary system ?
• Flaring : magnetic reconnection / flare of exciting star / accretion burst ?

ü Proper motion with VLBI (a few milliarcsec (mas) spatial resolution)• Enable us to detect tiny motions of a few mas yr-1 on disk/outflow/jet• Reveal 3-D velocity structure with LSR velocity information

ü Magnetic field strength and 3D structure• Circular polarization => Zeeman splitting• Linear polarization => Polarization vector• Convertible to the direction of the magnetic field axes

1. What’s advantages of maser
obs. for magnetic (B) field?

Importance of B field

Strong B field case(B0~17 µG; β0~10-1)ü Launch outflow/jets and magnetic braking• Removal of angular momentum• Maintain accretion through diskü Launch mechanism and morphology of outflow/jets
affected by the strength and the configuration of the
B field (Machida+ 08)• Outflow : low-velocity and hourglass-like, caused bystrong B field and the magnetocentrifugal force• Jet : high-velocity and well-collimated, caused byweak B field and the magnetic pressure gradient force

3D MHD simulations to understand the outflow/jet launching mechanism andmorphology in the star-forming core (Machida+ 08). These figures show the
relation among velocities, collimations, B field strength, and morphology.

Weak B field case(B0~17 µG; β0~10-5)

e.g.) Dust pol. obs.

(a)25

Low-mass
L1157(Hull+ 14)

Declination (J2000)

20

ü Aligned dust by B fieldü Measure polarization vector, convertible
to the B field on the plane of sky

15

10• e.g., “hourglass” shape (e.g., Girart+ 06)+68◦02 05

CO flow
08.0s

07.0s

256

• Impossible to direct measurement of thestrength of B field• may be estimated by comparing thegravitational force as an upper limit
at collapse phase• Hard to trace high-density area (> 108 /cc)

B field

06.0s

05.0s

Right Ascension (J2000)

45

High-mass40
W51 e2(Tang+ 09) 35+620h39m04.0s

TANG ET AL.

(c)

30
25

Declination (J2000)

ü Weak points

CO flow

dust pol.
@1.3 mm20
15
10

dust pol.
@0.87 mm05
02 00
Figure 5. Left panel: B-field maps in W51 e2 with S/N ratio between 2σIp and 3σIp (black

OMC1n4
NGC2024
S255
G10.6
M17SWHI
M17SWCNS106OHS106CNDR21OH1
DR21OH2
S140

05 35 16.8
05 41 44.2
06 12 53.7
18 10 28.7
18 20 22.9
18 20 25.0
20 27 28.4
20 27 29.5
20 38 59.9
20 38 59.9
22 19 17.1

–05 19 31–01 55 41
17 59 22–19 55 49–16 11 32–16 13 42
37 22 41
37 22 54
42 22 38
42 22 38
63 18 35

14.5
8.6
5.6
8.9
17.3
16.9
5.3
7.3
4.5
2.6
6.0

9.4
11.0
7.3
2.8
19.9
19.6
–1.7
–1.8
–4.7
–0.9
–6.3

1.5
2.2
2.3
5.8
4.3
3.3
2.0
1.9
2.3
2.3
2.4

0.45
0.45
2.5
6.5
1.3
1.3
1.7
1.7
3
3
0.9

0.03
0.04
0.18
0.19
0.11
0.10
0.07
0.07
0.15
0.15
0.05

14
5.9
3.7
14
6.0
6.0
1.0
1.0
1.7
1.7
6.0

2.8
1.4
4.2
16.4
4.2
3.7
0.4
0.4
1.5
1.5
1.0

e.g.) Zeeman splitting obs.

•

☞ a few detections in the high-density tracer

Stokes I (K)Stokes V (K)ü Weak points
•

18
18
500
2100
430
290
17
21
170
140
28

15
40
200
1300
440
230
55
50
160
160
63

1.5
line optical depth, this ratio should be 1; for a very small line
optical depth, the ratio will be 2.7. All but one of these ratios
are within the range 2.7–1 expected for LTE line strengths and1zero to infinite line optical depth; the one that is not has the
RI = 10 lines only very slightly too weak for LTE and low optical depth. The maximum line optical depth found by this tech0.5
nique is τ ≈ 0.5. We therefore compute the column density in
the N = 0 state assuming the RI = 10 lines are optically thin(see Turner & Gammon 1975). We then compute the total col0
umn density of (e.g.,
CN in Crutcher+all states by assumingthat all states are
99; Falgarone+08)
w3oh_xls Graph
excited with an assumed excitation temperature of 25 K. (These∗4
are warm, dense cores,
and several
T A arenot too far beLow-density(< 10/cc) of the: HI,OH
low 25 K in strength.) We then assume CN/H2 = 4 × 10−9 in
4-10value
6 /cc)
order to find NCN (Hof CN/H
High-density(10: CN2 ). This
2 is consistent withthose found by Turner & Gammon (1975) in dense, warm cores,
0.005
and matches the results found in OMC1 cores by Johnstone
et al. (2003). Finally, we compute the observed masses Mobsof the CN Zeeman sources from the radii and geometric mean
0.000
of Nn,r (H2 ) and NCN (H2 ), denoted N23 (H2 ) in the following. We
2also list for comparison the virial masses Mvir = 210r∆v M⊙ ,Splitcoefficient is much smaller than thermal
where r is expressed in pc and ∆v in km s−1 .
-0.005
As an example
the data, Fig. 1 shows the spectra ofline-width: ~1 ofHz/µG
W3OH. The Stokes I spectrum is the average (weighted by thesensitivity to the Zeeman
eﬀect)
of hyperfine
lines 1,to4, detect5, and 7
Signal-to-noise
ratio
is notenough-0.010(Table 1); these are the lines that have significant sensitivity to
-60
-55
-50
-45
-40
-35
circularpolarized
spectrum
the Zeeman eﬀect. The Stokes V spectrum is the equivalent averLSR Velocity (km/s)
age, where the non-Zeeman contributions to the observed V due
CN Zeemanspectra
spectra. The
plot isIthe
Stokesparameto gain imbalance and instrumental polarization (coeﬃcients C1 Fig. 1. W3OH
CN Zeemanof topStokes
(top)
and
ter
I
spectrum,andthebottomplot
isthe
StokesparameterV
spectrumand C2 in the fitting equation (Sect. 2)) have been removed. For
V (bottom)
in W3(OH)(histogram)and dI/dν (heavyline) scaled(Falgarone+for Blos = +1.1008).
mG.
W3OH the instrumental polarization contribution to Stokes V isthe equivalent of a 5.6 mG Zeeman signal for a (totally artificial)ü Energy quantum state is split by the B field
into multiple statesü Measure the strength of the B field directly!
ü To date in thermal lines, measured from HI,
OH, and CN
•
•

2.2
2.2
1.3
4.9
6.2
5.3
0.9
1.3
1.0
0.7
1.3

Advantages of the masersi.

Narrower line-width and brighter emission than thermal lines• Enable us to measure for small Zeeman split with high S/Nii.

Pumped in compact and high-dense cloud, called as “spot”• Enable us to trace higher-density area than thermal emissionsiii. Both linearly and circularly polarized emission• Full stokes parameters (I, Q , U, V) usable to determine 3D B field structureiv.

Combined with dynamics (3D velocity structure) information• Understand dynamical motions and magnetic structures, simultaneously

ii. High-density tracer (> 106 /cc)
W. H. T. Vlemmings: Zeeman splitting of 6.7 GHz methanol masers"üthenZeeman
106 /cc
measured by Green et al. was found on a
H2 > splitting779

B ∝ nH20.47 ±0.08

maser feature that, in lower5 resolution
observations, would be
8 /cc
•
OH
:
10
-10
(Cragg+02)
blended both positionally and spectroscopicallywith the brightest maser. As a results, the flux
averaged
Zeeman splitting mea4-10
9 /cc
•
CH
OH
:
10
(Cragg+surement is biased
toward a possibly negligible
magnetic05)
field
3of the brightest feature.
• H2O: 108-1011 /cc (Elitzer+ 92)
4.1.10. 81.87+0.78, W75N

0.47masers±0.08of(Vlemmings
6.7∝
GHznmethanol
the very active regionüTheB08) of masH2
sive star formation W75N have been mapped with the EVN(Minier
et al. 2000). Their
mapCrutcher
reveals that themasersmake• Consistent
with
(99)
relationup two distinct regions, an elongated region of ∼200 mas with
VLSR
6 km s−1 andfrom
a compact∼500 mas South-East• <Connect
lowfeature
to high-densityarea−1
at VLSR = 6.8 km s . The observations shown in Fig. 1 high102-106 /cc area
light the distinct nature of these maser features as the masers in
Crutcher (99)the linearly extended structure have B|| = 5.7 mG while those in
the compact region have B|| = 9.5 mG. W75N has been the target of numerous OH maser polarization observations indicating
another possible disc related field reversal and typical magnetic
field strengths of |B| ≈ 5–7 mG (e.g. Hutawarakorn et al. 2002;
Slysh et al. 2002). Magnetic field measurements during a OH
maser flare in W75N reveal the strongest OH maser magnetic Fig. 3. Magnetic field strength B in the massive star forming region
B vs the number
density
CepheusMagnetic
A measuredfield
fromstrangth
Zeeman measurements
as a functionof nH2 ,field B = 40 mG to date (Slysh & Migenes 2006).

☞Zeeman splitting measurements
extensible to high-density area !

4.1.11. 109.86+2.10, Cepheus A

the number
densityof neutralhydrogen.
TheAsolid
triangle indicatesnH2 inhigh-mass
SFR
Cepheus(Vlemmings
08).
the methanol maser measurement from the Eﬀelsberg observations, thenumber density is taken to be in the range typical of 6.7 GHz methanol

iii. Full stokes (linear and circular)ü Masers linearly and circularly polarized

3D B field structure• Linear : 2D pol. vector on the plane of sky• Circular : Strength and radial 1D pol. vector through Zeeman split

QM approach

M approach to Zeeman magnetic field orientation

RCP
definition

East

North
x

2989

Stokes V = RCP – LCP(the IAU convention)y

Direction of rotation forthe
IEEEIEEE
rhc−polarization
convention

z

Image credit: Green+ (14)Dow

Figure 2. The ‘right-handed’ axis system with the electric field of the wave
from equation (4) sketched in, and showing the direction of rotation of theelectric field vector, as seen by the observer, of RCP radiation under theIEEE convention. The alignment of the x and y axes with, respectively,

Eisbe
S
ElitzuElitzuElitzu
A
Field
Field
Field
Fish
Fish
Fujia
a
Garc
S
Gold
Gray
Gray
C
Gray
Gray
Gray
Gree
S
Hake

with line-of-sightvelocitiesof the masers
themotions with line-of-sight velocities of the masers indicate the motions
not constitutea simple straightline; the directionsof the indicatealignmentsof areceding
bipolarand
jet approachingwith a three-dimensional
space
speedtoof
presence of a bipolar jet with a three-dimensional space speed of presence
in both theclusters are almost
parallel21
21^ other
20 kmbuts shifted. Our analysis
the
basis
ofdirections
diagonalizationof the145 ^ 20 km s . Our analysis on the basis of diagonalization of the 145
each
by abouton
108
from
the
connecting
21
the two clusters, which
in
turn
is
almostparalleltothejetmotionsvariance–covariance matrix of the velocity vectors21 shows that the variance–covariancematrix of the velocity vectors shows that the(Figs 1are
and2). We foundthat theobserved withangularpattern angleof theof
vectors are concentrated towards a direction with a position angle of vectors
concentrated
towards
a direction
a position
H2O^masers
62.78 ^ 0.58 east from north and an inclination of 217.08 ^ 3.08 62.78
iswellfittedbyaprecessing
jet
model
(Fig.
0.58 east from north and an inclination of 217.08 ^3).
3.08
with respect to the sky plane. In this direction, the vectors are with
Theoreticalmodelssuggestthatacosmicjetiscreatedalongtherespect to the sky plane. In this direction, the vectors arerotation axis of a gas disk around an object such as a protostar or awhite dwarf so that the angular momentum of infalling material on
the disk can be released from the compact volume19,27. Adopting
such models for W43A, the jet will exhibit wiggling owing to theprecession of the disk.
Previous observations have inferred that stellar jets have alreadybeen formed approximately 1,000 years before an AGB star evolves
into a post-AGB star and starts the photoionization of its circumstellar envelope5. H2O masers in W43A are known to have existed• Spatial distribution
for at least 25 years11. However, the dynamical age of the jet in W43A
around 28 years as estimated from the distances to the tips of• Dynamics from 3D vel. structure istheonly
jet from the dynamical centre (about 900 AU) and the jet velocity

iv. Combined with 3D vel. structureü Totally understanding throughthe compact gas cloud “spot”• B field structure
Figure 2 Spatio-kinematics of H2O and OH masers in W43A. Assuming a pointsymmetrical bipolar jet, the mean velocity vector of the receding motion was calculated to Figure 2 Spatio-kinematics of H2O and OH masers in W43A. Assuming a pointbe 103.4 ^ 11.3 km s21, 52.6 ^ 16.1 km s21 and 86.5 ^ 3.4 km s21 in a, d and symmetrical bipolar jet, the mean velocity vector of the receding motion was calculated toradial directions, respectively. The mean velocity vector of the approaching jet is opposite be 103.4 ^ 11.3 km s21, 52.6 ^ 16.1 km s21 and 86.5 ^ 3.4 km s21 in a, d andto that of the receding component. Out of observed OH maser emission (hyperfine
radial directions, respectively. The mean velocity vector of the approaching jet is opposite
transitions in the ground state at 1.612, 1.665, 1.667 and 1.720 GHz), the 1.612-,
to that of the receding component. Out of observed OH maser emission (hyperfine
1.665- and 1.667-GHz lines were detected and only the 1.612-GHz line, which was thetransitions in the ground state at 1.612, 1.665, 1.667 and 1.720 GHz), the 1.612-,
strongest, could be imaged in the first and second epochs and shown here. After the
1.665- and 1.667-GHz lines were detected and only the 1.612-GHz line, which was thecorrelation, OH data with a velocity resolution of 0.36 km s21 were obtained. The angularstrongest, could be imaged in the first and second epochs and shown here. After the
resolution was 9 mas and 21 mas and the relative positions of the masers were measured
correlation, OH data with a velocity resolution of 0.36 km s21 were obtained. The angularwith a typical uncertainty of 1.2 mas and 2.2 mas in a and d, respectively. The OH masers2
resolution was 9 mas and 21 mas and the relative positions of the masers were measured
exhibit clear arcs and roughly fit a spherically expanding shell model with a radius ofwitha typical
uncertainty
of 1.2detectedmasofandmasH
in aO
andmasersd, respectively.
OH masers↑:
Propermotionsforin theTheevolved,500 AU and an expansion velocity of ,9 km s21. These parameters are generally
Figure3 Theangulardistribution
the H2.2
2O masers2detected on 10 October 1994, fitted
exhibit
clear
arcs
and
roughlyfitaspherically
expanding
shell
model
with
a
radiusof
7,8AGB
starpattern
W43A(Imai+↓: jetPrecessing
jet model
similar to, though slightly smaller than, those found in many OH/infrared stars . Thebythe spiral
expectedfrom a 02).
precessing
model. The modelled
jet hasfit
a to
21
21
and
an expansion
ofjet,9s an. inclination
These parameters
generally
dynamical age of the expanding shell was estimated to be around 2,600 years from the ,500
constant
velocity
ofstructure
150 km svelocity
andaxiskmwithof 398 withare
respect
to the3DAUvelocity
of aH
masers.
2Oe.g.) evloved AGB star W43A case• 3D vel. structure well fitted byprecessing jet model (Imai+ 02)• Toroidal B field structure
measured through linear pol. of
H O masers (Vlemmings+ 06a)

Model fit
to 3D vel.

7,8

with line-of-sightvelocitiesof the masers
themotions with line-of-sight velocities of the masers indicate the motions
not constitutea simple straightline; the directionsof the indicatealignmentsof areceding
bipolarand
jet approachingwith a three-dimensional
space
speedtoof
presence of a bipolar jet with a three-dimensional space speed of presence
in both theclusters are almost
parallel21
21^ other
20 kmbuts shifted. Our analysis
the
basis
ofdirections
diagonalizationof the145 ^ 20 km s . Our analysis on the basis of diagonalization of the 145
each
by abouton
108
from
the
connecting
21
the two clusters, which
in
turn
is
almostparalleltothejetmotionsvariance–covariance matrix of the velocity vectors21 shows that the variance–covariancematrix of the velocity vectors shows that the(Figs 1are
and2). We foundthat theobserved withangularpattern angleof theof
vectors are concentrated towards a direction with a position angle of vectors
concentrated
towards
a direction
a position
H2O^masers
62.78 ^ 0.58 east from north and an inclination of 217.08 ^ 3.08 62.78
iswellfittedbyaprecessing
jet
model
(Fig.
0.58 east from north and an inclination of 217.08 ^3).
3.08
with respect to the sky plane. In this direction, the vectors are with
Theoreticalmodelssuggestthatacosmicjetiscreatedalongtherespect to the sky plane. In this direction, the vectors arerotation axis of a gas disk around an object such as a protostar or awhite dwarf so that the angular momentum of infalling material on
the disk can be released from the compact volume19,27. Adopting
such models for W43A, the jet will exhibit wiggling owing to theprecession of the disk.
Previous observations have inferred that stellar jets have alreadybeen formed approximately 1,000 years before an AGB star evolves
into a post-AGB star and starts the photoionization of its circumstellar envelope5. H2O masers in W43A are known to have existed
for at least 25 years11. However, the dynamical age of the jet in W43A
is only around 28 years as estimated from the distances to the tips of
the jet from the dynamical centre (about 900 AU) and the jet velocity

iv. Combined with 3D vel. structure

Figure 2 Spatio-kinematics of H2O and OH masers in W43A. Assuming a pointsymmetrical bipolar jet, the mean velocity vector of the receding motion was calculated to Figure 2 Spatio-kinematics of H2O and OH masers in W43A. Assuming a pointbe 103.4 ^ 11.3 km s21, 52.6 ^ 16.1 km s21 and 86.5 ^ 3.4 km s21 in a, d and symmetrical bipolar jet, the mean velocity vector of the receding motion was calculated toradial directions, respectively. The mean velocity vector of the approaching jet is opposite be 103.4 ^ 11.3 km s21, 52.6 ^ 16.1 km s21 and 86.5 ^ 3.4 km s21 in a, d andto that of the receding component. Out of observed OH maser emission (hyperfine
radial directions, respectively. The mean velocity vector of the approaching jet is opposite
transitions in the ground state at 1.612, 1.665, 1.667 and 1.720 GHz), the 1.612-,
to that of the receding component. Out of observed OH maser emission (hyperfine
1.665- and 1.667-GHz lines were detected and only the 1.612-GHz line, which was thetransitions in the ground state at 1.612, 1.665, 1.667 and 1.720 GHz), the 1.612-,
strongest, could be imaged in the first and second epochs and shown here. After the
1.665- and 1.667-GHz lines were detected and only the 1.612-GHz line, which was thecorrelation, OH data with a velocity resolution of 0.36 km s21 were obtained. The angularstrongest, could be imaged in the first and second epochs and shown here. After the
resolution was 9 mas and 21 mas and the relative positions of the masers were measured
correlation, OH data with a velocity resolution of 0.36 km s21 were obtained. The angularwith a typical uncertainty of 1.2 mas and 2.2 mas in a and d, respectively. The OH masers
resolution was 9 mas and 21 mas and the relative positions of the masers were measured
exhibit clear arcs and roughly fit a spherically expanding shell model with a radius ofa typical
uncertainty
of 1.2detectedmasofandmasH
in aO
andmasersd, respectively.
OH masers↑:
Propermotionsforin theTheevolved↑:
convertedfromlinearpol. vectorof the with
,500BAUfield
and andirection
expansion velocity
of ,9 kms21. These
parameters
are generally
Figure3 Theangulardistribution
the H2.2
2O masers2detected on 10 October 1994, fitted
exhibit
clear
arcs
and
roughlyfitaspherically
expanding
shell
model
with
a
radiusof
7,8
Figure1: masersThe
spatiallinearpolarization
vectors
and inferredAGB
starpattern
W43A(Imai+↓: jetPrecessing
jet modelHin distribution,
W43A(Vlemmings+
06a).
↓: Toroidal
similarthoughslightly
smaller than,those foundin many
OH/infraredstars. TheBby
the spiral
expectedfrom a 02).
precessing
model. The modelled
jet hasfit
a to
2O to,
21
21
andan expansion
ofjet,9s an. inclination
These parameters
generally
dynamical
agedirection
ofinferred
the expanding
wasmasers
estimatedin
tothe
be around
2,600 years
fromthe ,500
constant
velocity
ofstructure
150 km svelocity
andaxiskmwithof 398 withare
respect
to the3DAUvelocity
of aH
masers.
field
model
H
O
maser
results.
2O
magnetic
field
of of
theshell
H 2O
jet of W43A.
HO
maser

Model fit
to 3D vel.

2

2

7,8

2. Remarkable works of maser
obs. for the magnetic fieldB field parameters of the masers

W. H. T. Vlemmin

OH

CH3OH

H2O

ν [GHz]1.6-1.7

6.7

22.2

Coefficient[Hz/µG]

2-3~10-4 *
(Jen 1951)

~10-3

Trace

Edeg of HII
regionAccretion
disk

Outflow/jetfraction L
fraction C~10-20%"~50-60%<1-20%"<1-5%<1-10%"<1-5%

Strength[mG]~10-50~10-100 *~10-1000

Note.

Strongly
affected by
RM* Largeuncertainty
of coefficientI(Q2+U2)1/2

V

Ref. --- e.g., Szymczak & Gerard (09); Surcis+ (12, 15); Vlemmings (08, +11)
H2O maser spectra in Cepheus A (Vlemming+ 06b)

Case 1. W75 N~ rapidly evolution of outflow
morphology and B field structures ~High-mass star-forming region W75 N
746

TORRELLES ET AL.

standard procedures.
In particular, individualü PartusingofAIPS
CygnusX region
spectral channel maps were made from the 3.1 MHz bandwidth. The resulting cube (63 channels) of the H O maserü Distance:
kpc(Rygl+
12)a Ðnal2 velocity
line was then1.30
Hanningsmoothed,
givingresolution of ^1.2 km s~1. This smoothing in velocity wasapplied to reduce the Gibbs ringing e†ect due to the strongü ThreeYSO candidates at different
and narrow H O masers (see Thompson, Moran, &2
Swenson 1986 for a discussion of these e†ects). These
evolutionary
10)
Hanning-smoothedphasedata were (Carrasco-Gonzalez+
used to analyze the spatio-Vol. 489

1.3 cm continuum with VLA(Torrelles+ 97)
VLA 1 (W 75N[Ba])kinematic distribution of the H O masers in the region.
2• VLA1: oldest

3. RESULTS• Index:3.1.
-0.4
±0.1
=>Emission
optically thin,
1.3 cmContinuum
In Figure 1 we show a contour map of the continuum
free-free
emission with natural weighting of the 25 MHz bandwidth(u, v) data (the ““ e†ective ÏÏ bandwidth was 21.9 MHz, 7• VLA2:
youngerthan
VLA1
channels ] 3.125
MHz). The
synthesized
beam is 0A. 1, andthe achieved rms noise of the image is 0.16 mJy beam~1.
Three sources are detected. We will call them hereafter,from north to south, VLA 1, VLA 2, and VLA 3, respectively. VLA 1 is elongated, with a deconvolved size of D0A. 4] 0A. 1 (P.A. 43¡), while VLA 3 shows a bright core plus
extended emission, with a deconvolved size of 0A. 09 ] 0A. 04(P.A. 152¡). VLA 2 appears unresolved ([0A. 1). In Table 1
the observed and derived parameters of these three sources
at 1.3 cm are listed.
The positions of VLA 1 and VLA 3, coincide, respectively, with the sources W75N(Ba) and W75N(Bb) detected
previously at 3.6 cm with 0A. 5 resolution by Hunter et al.
(1994) and indicated by crosses in Figure 1. On the other
hand, VLA 2 lies almost in between VLA 1 and VLA 3 but• Index: 2.2 ±0.3 => optically thick,free-free• VLA3: youngest

DECLINATION (B1950)

42 26 58.5

58.0

VLA 2

57.5

VLA 3 (W 75N[Bb])57.0• Index: 0.6 ±0.1 => thermal jet

20 36 50.08

50.06

50.04
50.02
50.00
49.98
RIGHT ASCENSION (B1950)

49.96

FIG. 1.È1.3 cm continuum contour map of W75N(B). Contours are[3, [2, 2, 3, 4, 5, 6, 7, 8, 15, 20, 25, 30, 35, 40, 45 times 0.16 mJy beam~1,
the rms of the map (beam \ 0A. 1, shown in the top right-hand corner).

H2O maser distributions and motions
No. 2, 2003

ü VLA1 : elongated NE-SW direction•

VLA1

Bipolar motion toward NE-SW

ü VLA2 : spherical morphology•

Spherically expanding motion

VLA1

VLA2

EVOLUTION OF OUTFLOW COLLIMATIONVLA2Torrelles+ (03)

Rapidly change of spatial distribution andB field structure of H2O maser in VLA2
The Astrophysical Journal, 767:86 (9pp), 2013 April 10

ü Spatial distribution of H2O maser in
VLA2 in ~8 yrs (Kim+ 13)• Spherical ⇒ Elongated to NE-SW

Figure 5. Elliptical fits for the H2 O masers in VLA 2 observed with VLBI in
epochs 1999.3 (T99), 2005.9 (S05), and 2007.2 (K07) by Torrelles et al. (2003),
maps
at 3respectively.
epochs
Surcis et al.VLBI(2011), andthis work,(Torrelles+ 03; Surcis+ 11; Kim+ 13).

K07). This corresponds to expanding velocities in the intervals

Rapidly change of spatial distribution andB field structure of H2O maser in VLA2

G. Surcis et al.: Rapidly increasing collimation and magnetic field changes of a protostellar H2 O maser outflow

n of the H2 Oümasers
around2 in rapidly
epoch 2005.89
S11) structure
and in epoch(right panel;
Surcis+(14) VLA
detectedchanges(leftof panel;the B fieldin 72012.54
yrs
elliptical fits of the H2 O maser distributions observed in the past 13 years is also shown (see Fig. 1 for more d• the direction of the B field : +18 ⇒ +57 deg"ty bar on the right of both panels shows the same velocity range. Four ellipses are drawn, which are assumed
thearestrengthof ofthefieldfit:of345
mG⇒ 128 mGeference position). •They
the results
theBbest
the H
2 O masers detected by T03 (epoch 1999.25; red dagreen dotted ellipse), K13 (epoch 2007.41; blue dot-dashed ellipse), and the present work (epoch 2012.54; blRapidly change of spatial distribution andB field structure of H2O maser in VLA2
The Astrophysical Journal, 767:86 (9pp), 2013 April 10

ü Spatial distribution of H2O maser in
VLA2 in ~8 yrs (Kim+ 13)• Spherical ⇒ Elongated to NE-SW

ü B field structure of H2O maser in
VLA2 in ~7 yrs (Surcis+14)• Direction : +18 ⇒ +57 deg"
• Strength : 345 mG ⇒ 128 mG"☞short-lived, isotropic, ionizedwind in the strong B field
predicted by MHD simulation ?Figure 5. Elliptical fits for the H O masers in VLA 2 observed with VLBI in(e.g., Machida+ 08; Seifried+ 12)• Collimated as being evolved ??

2

epochs 1999.3 (T99), 2005.9 (S05), and 2007.2 (K07) by Torrelles et al. (2003),
maps
at 3respectively.
epochs
Surcis et al.VLBI(2011), andthis work,(Torrelles+ 03; Surcis+ 11; Kim+ 13).

K07). This corresponds to expanding velocities in the intervals

Verified by radio continuum obs.
–9–ü 1.3 cm continuum distribution was
also changed in ~20 yr in VLA2

0.2

VLA 2

0.1

(Carrasco-Gonzalez+ 15)

K Band1996

0.0• Spherical ⇒ Elongated to NE-SW
DEC Offset (arcsec)

ü Verified short-lived, isotropic,
ionized wind whose morphology
evolves into elongated to NE-SW
inferred from H2O maser
observations (dynamics & B ) !!

−0.1
−0.2
−0.3
0.2

K Band
2014

0.1
0.0
−0.1
−0.2

260 AU

−0.3
0.2

0.1

0.0 −0.1 −0.2 −0.3 −0.4
RA Offset (arcsec)

Carrasco-Gonzalez+ (15)Fig. 2.— Comparison of the K band continuum emission of VLA 2 in epochs 1996 (top) and2014 (bottom). The (0,0) position is the same as in Fig. 1. Contours are 30, 40, 50, 60, 70, 80, and 90% of
the peak intensity in 1996 (1.42 mJy beam 1 ) (RMS = 150 µJy beam 1 ), and 5, 10, 20, 30, 40, 50, 60, 70,
80, and 90% of the peak intensity in 2014 (0.82 mJy beam 1 ) (RMS = 10 µJy beam 1 ). Both maps wereAlignment of the B direction ?
A&A 565, L8 (2014)+49 (±15) deg+57 (±21) deg

view of the 22üGHz
H2 O (14)maserfeaturesalignment
detected aroundthe direction
radio source
VLA 1and(leftVLA2
panel) and VLA 2 (Surcis+detectedof B fieldin VLA1
h
m s
◦
′ ′′
n is α2000 = 20 38• 36.
435 andδ2000(±15)= 42deg,
37 34.VLA2
84 (seeSect.(±21)2). Theoctagonal symbols are the identifi
VLA1
: +49
: +57
deg"
rk scaled logarithmically according to their peak flux density (Tables A.1 and A.2). The linear polarizatio• Nearly
perpendicularfilament
structuretracedcornerby NH
emission
cording to polarization
fraction
Pl , are overplotted.
In thebottom-rightof3 bothpanels??the error-weighCase 2. Statistical study in starformation scale~ relationship of the orientations
between B field and outflow axes ~B field vs outflow axes

Fig. 7. Left: probability distribution function (PDF, top panel) and cumula
between the PA of the CH3 OH maser distribution and the linear polarization
angle between the PA of the CH3 OH maser distribution and the outflow ax
random orientation of outflows and magnetic fields, i.e. all angular diﬀeren
be found in Table 3.

ü Measured B field of CH3OH masersin ~20 high-mass YSOs (Surcis+ 12, 13, 15)fü Orientation of the B field along theoutflow axes, preferentially•

At least, on scales of 10-100 au
G. Surcis et al.: Magnetic field and outflows: first statisticalresultset al.: Magnetic field and outflows: first statistical results
G. Surcis

A
fu
p
N
P
A
c

R

A

Fig. 5. Leftaround
panel: IRAS
view ofthe CH3 OH maser 1features
around S231
(Table identify
A.4). Right panel: zoom-in view of group A1. Same symbols
2. Left panel: view of the CH3 OH maser features detected
06058+2138-NIRS(TabledetectedA.1). Triangles
symbolsFig. 8. Probability distribution function (PDF, top panel) and cumulaComparison of the B field orientation from CH3OH maser
PDF and CDF of the projected angle between
tive distribution function (CDF, bottom panel) of the projected angle
obs.
to theoutflowaxes(Surcis+themagneticBfield field
and theaxesaxes(Surcis+ntation of themagnetic
field (Φ, see Sect. 6.2.1)
is alsoreported, the13).
two dashed segments indicates the uncertainty.
The twothe
arrowsindicate
betweenand outflow
the outflow(|PAout 13).
− ⟨ΦB ⟩|). The◦

Fig.peak
2. Thearrow
indicates
the A.1).
directionof theblue-shifted
lobe of the(PAout = 133 ; Ginsburg et al. 2009).The dashed line is
to intheirflux
density(TableMaser
LSR
radial velocities
areHindicated
2 -outflow by
3 OH maser features scaled logarithmically according as
C18 O−1
the best
linear et
fit al.
of the
CH3 A
OH4 maserfeaturesof group
A (PAACH= 28◦ ± 8◦ ),while
the dotted line is the best linear fit of the CH3 OH maser= +3.9 km
s−1 , Saito2007).
Jy beamsymbolis plottedforillustration.
Thelinearor (the assumed velocity of the YSO is Vlsr
3 OH◦
147the± right-bottom
12◦ ).
features of groups
B, P
C,l , and
(PABCDarization vectors, scaled logarithmically according to polarization
fractionare Doverplotted.
corner the error weighted
CH3 OH =On
B

direction of the red- and blue-shifted lobe of the bipolar outflow (PAout = 130◦ ; Wu et al. 2010). The dashed line is the best linear fit of the◦◦dashed line is the CDF for random orientation of outflows and magnetic
3 OH maser features of group A (PACH3 OH = 78 ± 7 ). Right panel: zoom-in view of group A.

As we have already mentioned in Sect. 4, the 6.7-GHz

B
B
B
B
C
C
C
D
D
D
G
G

Case 3. Statistical study in the
Galactic scale~ Galactic structure of the B field ~ded from http://mnras.oxfordjournals.org/ at Ibaraki University Library on October 18, 2016

ith the exception of the low significance measurements towards−0.418. The magnetic field direction is discussed in full in Secbut under the current conventions would be directed away from theositive measurements and towards for negative. Galactic rotation
ise in this figure. The Sun is located at (0,8.4).

smooth symmetry of the rotation measures across Galact
tudes, would argue against these longitudes being biased b
object with a different field orientation.
The magnetic field measurements in this region there
ply that the techniques of Zeeman splitting and rotation m‘MAGMO’ project throughZeeman splitting of OH masers

Figure 3. Spectra of the RHCP (solid blue) and LHCP (red dashed) maser features. ‘S/L’ denotes sidelobe response. The flux density of 285.263−0.050
should be scaled by a factor of 1.08 to account for the primary beam correction. The flux densities of 291.610−0.529 and 291.654−0.596 should be scaled byfactors of 1.01 and 1.02, respectively, to account for the primary beam correction. The flux density of 292.259−0.836 should be scaled by a factor of 6.58 toaccount for the primary beam correction.

Green+ (12)⃝C 2012 CSIRO, MNRAS 425, 2530–2547
C 2012 RAS
Monthly Notices of the Royal Astronomical Society ⃝• MAGMOthe directions
Magneticof measures
the Milky
Way throughOH masers(e.g., onGreen+
12) Hα em. Comparisonof magnetic: field
fromfield
rotationand Zeeman
splitting measurements
overlaid
the composite
er (2003) using•thePilot
Southern
H-AlphaSurvey Atlassources
data of Gaustad
et al. (2001).|B
The|~1-10
Hα emission
indicates
regionsof ionized hydroge
survey: 6Skyhigh-mass
280<l<295°,mG,
Sameorientation||

4. Summary

Summaryü B field observations of the masers is usable••••

Narrower line-width and brighter emission than thermal one
Pumped in compact dense cloud (106-1011 /cc)
Both linearly and circularly polarized (full stokes I, Q , U, V)
Combined with dynamics (3D velocity structure) information

ü Remarkable works of the maser B field obs.
• W75 N : short-lived, isotropic, ionized wind in the strong B field whosemorphology evolves into elongations (e.g., Surcis+ 14; Carrasco-Gonzalez+ 15)• Statistical study (e.g., Surcsis+ 12, 13, 15; Green+ 12)• in the star formation scale : Alignment of the B field along the outflow axes
• in the Galactic scale : Zeeman splitting measurements throughout the Milky Way‘MAGMO’