IRSFによる
セイファート銀河NGC1068の偏光観測
村⽥勝寛（東⼯⼤）

nearby spiral galaxy
with active galactic nucleus(AGN)

Hubble Space Telescope
blue : Hα emission
yellow: I band (~0.8µm)

This poster 30

log (Polarizedflux)
Polarized intensity
2.5

20

2.0

10

1.5

AGN

0

1.0

−10log count (ADU)

offset Dec (arcsec)

spiral arms

0.5−201 kpc

bipolar cone

We found two distinct −30
polarization components.
30 arms
20100−10−20
ü polarization of spiral
R.A. (arcsec)
ü polarization of bipolarCenter:
coneR.A.offset02 42 40.73 Dec −00 00 48.0

0.0

−0.5−30

conclusion
The polarization of the bipolar cone may be caused by the scattering of AGN light.
The polarization of the arms may be caused by dichroic extinction of dust grains.

We can knowi ) magnetic field of AGN host galaxyii ) scattering of AGN light by the hostgalaxy mediumoptical polarization of merging spiral galaxies M51
contour : V band total flux
solid short lines : polarization vector
length -- polarization degree
direction -- polarization angleM51b

The polarization follows the spiralarms.

M51a

If we assume this polarization iscaused by dichroic extinction ofelongated dust grains which isaligned by large scale magnetic
field, the polarization angle follows
magnetic field.
Scarrott+87

à We can know magnetic fieldusing polarization.

NIR polarization ofcentral ~1kpc of NGC1068• The polarization around theAGN shows circularsymmetric pattern centeredabout the AGN.
• Circular-symmetricpolarization is a signature of
the scattering of light frombright source.
à The polarization may

be caused by thescattering of the AGN
light.
(Simpson+02)

In order to investigate magnetic field and scattering of AGN light,

Imaging polarimetry (linear polarization)of AGN host galaxies
using IRSF/SIRPOL
Target AGN host galaxies
20 galaxies listed in the right tablenearby and bright AGN host galaxies
Detection of Polarization
NGC1068, Circinus galaxy, NGC1808

In this poster,I will show you preliminary results of NGC1068.
The polarization is detected in the central 50”x50”
region around the AGN.

AGN

spiral arms

50” x 50”

“bipolar cone“of ionized gas
which extends from SW to NESchinnerer+2000

Results

PolarizationPolarization
vector of IRSF H band30The polarization degree is P=1-4%.

contour: total flux
short lines : polarization vector

offset Dec (arcsec)

2010Polarization due to dichroic
extinction of elongated dust
grains in our galaxy is expected
to be < 0.02 % from theextinction toward NGC1068.
(Packham+97).

0−10−20−3030

20100−10offset R.A. (arcsec)−20−30

Polarization with S/N>2 are shown in this figure.

à The polarization of NGC1068 is
not affected by foreground dustof our galaxy.Resultslog (Polarizedflux)
Polarized intensity
2.530

There are two distinct
polarization components.
• spiral arms
• bipolar cone

20

2.0

10

1.5

0

1.0

−100.5−20
1 kpc

bipolar cone

−30

0.0

−0.53020100−10−20−30offset R.A. (arcsec)
Center: R.A. 02 42 40.73 Dec −00 00 48.0

log count (ADU)

offset Dec (arcsec)

spiral arms

Polarized flux in the bipolarcone is much brighter than
the spiral arms.
The polarized flux of thebipolar cone decrease withthe distance from the AGN.
à The polarization of thebipolar cone may be relatedwith AGN light.

ResultsJ band

H bandPolarization

Polarization

30302020201010100−10−20−3030offset Dec (arcsec)

30offset Dec (arcsec)

offset Dec (arcsec)

Polarization

Ks band0−10100−10offset R.A. (arcsec)−20−30−3030−10−20−20200

20

100−10offset R.A. (arcsec)−20−30−3030

20

100−10offset R.A. (arcsec)

The polarization pattern of J band is similar with H band.
In Ks band, we detected polarization only in the bipolar cone.
The bipolar cone polarization is similar with the J and H band.

−20−30Results

30

2.5

202.0

10

1.5

0

1.0

−100.5−20

Packham+97
AAT (Anglo-Australian Telescope)log count (ADU)

offset Dec (arcsec)

our obs.
with IRSF
Polarized intensity

Scarrott+91

0.01 kpc
−30

−0.5

30

20

100
−10−20−30
offset R.A. (arcsec)
Center: R.A. 02 42 40.73 Dec −00 00 48.0

the largest map of polarizationin the previous NIR polarimetry ofNGC1068

ResultsOur polarization of J and Ks band is also consistent
with the previous NIR observation.
J bandH bandKs bandPolarization

Polarization

10555

1997MNRAS.288..375P

0offset Dec (arcsec)

10offset Dec (arcsec)

1000−5−5−5−10−10−101050−5offset R.A. (arcsec)−101050−5offset R.A. (arcsec)−101050−5offset R.A. (arcsec)

Anglo-Australian Telescope（AAT） Packham+97
1997MNRAS.288..375P

offset Dec (arcsec)

Polarization−10Discussion
polarization
vectoron polarized flux
Polarized
intensity
2.510- Determinaion of IR-nebula's illumina- Dust properties- Background star polarimetry (E ! B)
- Magnetic field structure in star-formin- Synchrotron radiation (E ! B)
circular-symmetricpolarization- Magnetic fieldstructure (e.g., SNR)

2.0

1.5

0

1.0

log count (ADU)

offset Dec (arcsec)

5Spinning nonspherical dust grains

0.5−50.0

Scattered light polarization

Polarizationaligned dust

from Tamura-san’s slide−10−0.5105•

0−5−10offset R.A. (arcsec)Center:
R.A. 02 42 40.71 in
Dec−00bipolar
00 48.0 cone shows circular-symmetric pattern and its
The polarizationthe•The polarized flux decreases with the distance from the AGN.

center is AGN. The circular-symmetric pattern is a signature of thescattering of light from bright source.

à The polarization may be caused by the scattering of AGN light by bipolarcone medium (dust and/or electron)

Discussio
npolarization
vectoron polarized flux
Polarizedintensity
2.5

2010

1.50

1.0

−100.5log count (ADU)

2.0

The polarization of spiral armsdose not show circularsymmetric pattern.
But it follows the spiral arms.

à The polarization is NOT
0.0 due to scattering of AGN
light.

−20−0.5

20

100−10−20
offset R.A. (arcsec)
Center: R.A. 02 42 40.73 Dec −00 00 48.0

Another polarization mechanism isnecessary for the arm polarization.
It may be dichroic extinction byelongated dust grain.

Dichroic extinction by elongted dust grains
which are aligned by magnetic field cause polarization.

9/10Polarization direction∝ magnetic field BBmagnetic fieldpolarized light

The polarization degree increases
with increasing dust extinction.

18/18•

We observed NGC1068 with IRSF/SIRPOL.

•We detected two distinct polarization components, spiral arms andbipolar cone, in J, H and K band within central ~50”x50” region.

•The polarization of the bipolar cone may be caused by the scattering of
the AGN light by the cone medium.

•Polarization in the spiral arms may be caused by dichroic extinction ofelongated dust gains which are aligned with magnetic field.

à Magnetic field may follow the spiral arm in NGC1068.