Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/research/cena/documents/presentations/gaensler.pdf Дата изменения: Wed Jul 29 05:49:35 2009 Дата индексирования: Fri Nov 27 09:06:20 2009 Кодировка: Поисковые слова: m 57

Faraday Rotation of Radio Galaxies Behind the Lobes of Centaurus A
Bryan Gaensler
Sydney Institute for Astronomy School of Physics The University of Sydney
+ Ilana Feain, Ronnie Jansson, Glennys Farrar, Ron Ekers, Tara Murphy, Ray Norris, J-P Macquart, Tim Cornwell,JЭrgen Ott, Enno Middelberg, Melanie Johnston-Hollitt


Faraday Rotation
· · · · Optical starlight polarisation Synchrotron emission / polarisation Infrared dust polarisation Zeeman splitting

}

B (orientation, but not direction) B (long integrations, high-density regions)

· Faraday rotation & rotation measure (RM) are powerful probes of B

=

0

+ RM
0 L 2

2

RM = K
80 rad m

n e B dl

(

ne 10 3 cm

3

)

B 1 G

L 100 kpc

- radio wavelengths: no attenuation of radiation - "absorption" experiment - provides direction of B - weighted by ne

Philipp Kronberg / Physics Today


Background AGN

Phoenix Deep Field (Hopkins et al. 2003)


The Rotation Measure Grid

RMs through the Large Magellanic Cloud (Gaensler et al. 2005)


Rotation Measure Synthesis

· Faraday dispersion function (Burn 1966) · Fourier spectropolarimetry (Killeen et al. 2002) · RM synthesis (Brentjens & de Bruyn 2005)


Ambiguities


Real ATCA Data

SUMSS J052216-672737 (Gaensler et al. 2005)


Results (I)


Results (II)


Results (III)


Results (IV)


Results (V)


Faraday Rotation Towards Cen A
· Cen A at 1.4 GHz: - 1005 background src's >3 mJy · 281 sources with polarisation >7


Faraday Rotation Towards Cen A
· Cen A at 1.4 GHz: - 1005 background src's >3 mJy · 281 sources with polarisation >7 · RM = -57 rad m-2, stdev = 30 rad m-2 · 93 RMs behind Cen A; 188 outside


Faraday Rotation Towards Cen A
· Cen A at 1.4 GHz: - 1005 background src's >3 mJy · 281 sources with polarisation >7 · RM = -57 rad m-2, stdev = 30 rad m-2 · 93 RMs behind Cen A; 188 outside · Fit linear gradient to outside RMs of 6 rad m-2 deg-1


Faraday Rotation Through Lobes
· RM = -57 rad m-2, stdev = 30 rad m-2 - lobes: -40 to -70 rad m-2
(Cooper et al. 1965; Clarke et al. 1992

- lobes: -60 ± 2 rad m-2
(Gardner & Davies 1966; Simard-Normandin et al. 1981; Vinyaikin & Abramov 1991)

- nearby sources: ~ -60 rad m-2
(Johnston-Hollitt et al. 2004; Short et al. 2007)

|RM

lobes|

< 10 rad m-2
0 L

RM = K
-L -B

n e B dl

180 kpc
lobes

1 G (Hardcastle et al. 2009)
lobes

ne,

< 7 x 10-5 cm-3


RM Structure Function
DRM

()

= [RM

(

+

)

RM

( )]

2

· Plot DRM vs. : - fluctuations as function of angular scale


RM Structure Function
DRM

()

= [RM

(

+

)

RM

( )]

2

· Plot DRM vs. : - fluctuations as function of angular scale


Enhanced RMs on SW Rim?
· Structure is due to RM 30 rad m-2 on scale of 0.5o along southwest rim · Coincides with abrupt transition in polarisation & total intensity properties
(see Rudnick & Blundell 2003)

· If associated with Cen A,
RM

=

0.81 n e, skin 3 10 -3 cm

-3

Bskin G

L l rad m kpc kpc

-2

(e.g., Gaensler et al. 2001)

-L

200 kpc, l ne,skin . Bskin

30 kpc 8 x 10-4 G.cm-3

For n
Parkes 5 GHz polarisation (Junkes et al. 1993)

e,skin skin

10-3 cm-3 (Bouchard et al. 2007), 0.8 G

B


Summary & Further Work
· 1005 background radio sources over ~40 deg2 - Faraday rotation measures for 281 polarised sources - 188 RMs for Galactic foreground; 93 RMs thru Cen A lobes · Ordered B
Galactic

produces small deflections of UHECRs ne
, lobes

· |RMlobes| < 10 rad m-2

< 7 x 10-5 cm-3
skin

· Fluctuating RMs on SW rim: thermal cocoon, B

0.8 G ?

· RM and pol frac of diffuse radio emission from Cen A lobes · Foreground emission measure map from WHAM survey "Polarisation Sky Survey of the Universe's Magnetism" (POSSUM) · ASKAP large survey: 3 million RMs over 30,000 deg2 · 20 hour observation of Cen A would yield ~4000 RMs · Can be repeated for smaller / more distant radio galaxies
C. Fluke