1998A&A...329..809A


Query : 1998A&A...329..809A

1998A&A...329..809A - Astronomy and Astrophysics, volume 329, 809-820 (1998/1-3)

Large rotation measures in radio galaxies at z > 2.

ATHREYA R.M., KAPAHI V.K., McCARTHY P.J. and VAN BREUGEL W.

Abstract (from CDS):

We have carried out multifrequency radio polarisation imaging of a sample of 15 radio galaxies at z > 2 from the MRC/1Jy sample using the VLA. We report here the discovery of large rotation measures (RM) in a considerable fraction of the high redshift radio galaxies. Using the difference between the RM values of the two radio lobes in each source and statistical arguments, we show that the Faraday screens responsible for the RMs are most likely to be in the vicinity of the radio sources themselves. Four of the 15 galaxies show intrinsic (redshift corrected) RMs in excess of 1000rad/m2 with the highest value of ∼6000rad/m2 in 1138-262 at z=2.17. These observations suggest that the environments of the radio galaxies at z>2 have micro gauss magnetic fields correlated over many kpc (>5-10), at least. We have discussed the problems due to the short time available at those redshifts for the various mechanisms, which are believed to generate and correlate strong magnetic fields on large scales, to operate. In particular, we argue that, unlike at low redshifts, cluster cooling flows are unlikely to have a role in forming deep Faraday screens at high redshifts. It is not clear if the dynamo mechanism is capable of generating such fields in the ambient medium around the radio sources. It appears plausible that condensates of magnetised plasma (galactic or subgalactic sized) are the deep Faraday screens responsible for the observed RMs. We suggest that plasma clumps of as small as 109M in the path of the radio jet may generate very large RMs. The presence of such strong and large scale magnetic fields in the medium around the radio sources at such early epochs poses a considerable challenge to models of the origin of magnetic fields in the Universe.

Abstract Copyright:

Journal keyword(s): galaxies: magnetic fields - radio continuum: galaxies - cosmology: observations

Simbad objects: 23

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Number of rows : 23
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 PMN J0017-2238 rG 00 17 58.19 -22 38 04.6           ~ 16 1
2 3C 48 QSO 01 37 41.2996631208 +33 09 35.080388820   16.62 16.20     ~ 2673 2
3 PMN J0142-2531 rG 01 42 41.21 -25 30 34.3           ~ 22 1
4 MRC 0156-252 rG 01 58 33.480 -24 59 32.01   22.7       ~ 49 0
5 QSO B0237-2322 QSO 02 40 08.1743783856 -23 09 15.729012036   16.78 16.63     ~ 489 0
6 NVSS J031812-253509 rG 03 18 12.00 -25 35 09.0   23.6 23.8     ~ 75 2
7 [VV96] J035111.8-205800 QSO 03 51 11.8 -20 58 00     17.90     ~ 22 1
8 LEDA 2823818 Sy2 04 08 51.4 -24 18 17     22.40     ~ 77 2
9 4C 41.17 rG 06 50 52.098 +41 30 30.53           ~ 322 1
10 3C 194.0 QSO 08 10 03.3449360136 +42 28 03.220633740   24       ~ 102 1
11 NVSS J090530+340756 rG 09 05 30.1 +34 07 57   24.0 23.800 23.500   ~ 154 1
12 PMN J1108-2605 rG 11 08 30.40 -26 05 04.0           ~ 13 1
13 NAME Spiderweb Galaxy AGN 11 40 48.3 -26 29 09     22.00     ~ 264 1
14 QSO B1143-245 QSO 11 46 08.1033450360 -24 47 32.900532360   17.97 18.0 17.20   ~ 116 1
15 PMN J1326-2631 rG 13 26 54.68 -26 31 42.1           ~ 14 1
16 3C 286 Sy1 13 31 08.2883506368 +30 30 32.960091564   17.51 17.25     ~ 4059 2
17 3C 295 Sy2 14 11 20.467 +52 12 09.52   22.34 20.80 18.54   ~ 946 5
18 NAME Cyg A Sy2 19 59 28.35645829 +40 44 02.0966496   16.22 15.10     ~ 2237 2
19 LEDA 2830476 Sy1 20 27 59.5 -21 40 56   22.4       ~ 73 1
20 PMN J2039-2514 rG 20 39 24.49 -25 14 30.7           ~ 19 1
21 LEDA 2830749 rG 21 06 58.16 -24 05 11.3   23.0       ~ 72 1
22 NVSS J214216-285839 rG 21 42 16.67 -28 58 40.4           ~ 13 1
23 ICRF J233355.2-234340 BLL 23 33 55.2379642584 -23 43 40.660470084   16.45 17 11.21   ~ 155 1

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2022.05.22-00:08:25

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