2000A&A...355..128C


Query : 2000A&A...355..128C

2000A&A...355..128C - Astronomy and Astrophysics, volume 355, 128-137 (2000/3-1)

Regular magnetic fields in the dwarf irregular galaxy NGC 4449.

CHYZY K.T., BECK R., KOHLE S., KLEIN U. and URBANIK M.

Abstract (from CDS):

We present a high-resolution VLA study of the total power and polarized radio continuum emission at 8.46 and 4.86 GHz of the irregular galaxy NGC 4449, known for its weak rotation and non-systematic gas motions. We found strong galaxy-scale regular magnetic fields, which is surprising because of a lack of ordered rotation required for the dynamo action. The strength of the regular field reaches 8µG and that of the total field 14µG, comparable to that of the total magnetic field strength in radio-bright spirals. The magnetic vectors in NGC 4449 form radial ``fans'' in the central region and fragments of a spiral pattern in the galaxy's outskirts. These structures are associated with large regions of systematic Faraday rotation, implying genuine galaxy-scale magnetic fields rather than random ones compressed and stretched by gas flows. The observed pattern of polarization B-vectors is similar to dynamo-type fields in normal spirals. Nonstandard, fast dynamo concepts are required to explain the observed field strengths, though it is unknown what kind of magnetic field geometry can be produced in slowly and chaotically rotating objects. The so far neglected role of magnetic fields for the dynamics and star formation in dwarf irregulars also needs to be revised.

Abstract Copyright:

Journal keyword(s): galaxies: magnetic fields - galaxies: irregular - galaxies: individual: NGC 4449 - radio continuum: galaxies - polarization

Errata: erratum vol. 356, p. 757 (2000)

CDS comments: probable supernova remnant = EQ J122806+440339

Simbad objects: 7

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Number of rows : 7
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 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 15990 1
2 6C 121638+484640 QSO 12 19 06.4157892648 +48 29 56.160738384   21.22 20.49 19.90   ~ 124 1
3 UGC 7577 GiG 12 27 41.8796163840 +43 29 58.136511408 13.75 13.10 12.7 12.33   ~ 242 0
4 EQ J122806+440339 SR? 12 28 06.7 +44 03 39           ~ 1 0
5 NGC 4449 EmG 12 28 11.118 +44 05 36.81 10.11 9.98 9.64 9.45   ~ 1071 1
6 NGC 4631 GiP 12 42 08.009 +32 32 29.44   9.78 9.19 9.10   ~ 1024 2
7 3C 286 Sy1 13 31 08.2883506368 +30 30 32.960091564   17.51 17.25     ~ 4059 2

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2022.05.20-19:58:46

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