Issue |
A&A
Volume 444, Number 3, December IV 2005
|
|
---|---|---|
Page(s) | 739 - 765 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20053556 | |
Published online | 05 December 2005 |
Magnetic fields in barred galaxies
IV. NGC 1097 and NGC 1365
1
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: rbeck@mpifr-bonn.mpg.de
2
School of Mathematics and Statistics, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK
3
Department of Physics, Moscow State University, 119992 Moscow, Russia
4
XMM-Newton Science Operations Centre, European Space Astronomy Centre (ESAC), European Space Agency, PO Box 50727, 28080 Madrid, Spain
5
School of Mathematics, University of Manchester, Manchester M13 9PL, UK
6
Pushchino Radioastronomy Observatory, Astro Space Center, 142292 Pushchino, Russia
Received:
2
June
2005
Accepted:
2
August
2005
We present cm and
cm radio
continuum maps in total and polarized intensity of the barred
galaxies NGC 1097 (at 2´´–15´´ resolution) and NGC 1365
(at 9´´–25´´ resolution). A previously unknown
radio galaxy southwest of NGC 1097 is reported.
Apart from a smooth faint envelope and a bright central region,
both galaxies exhibit radio ridges roughly overlapping with the massive dust
lanes in the bar region. The contrast in total intensity across the radio ridges
is compatible with compression and shear of an isotropic random magnetic field,
where the gas density compression ratio is approximately equal to 4
and the cosmic ray density is constant across the ridges.
The contrast in polarized intensity is
significantly smaller than that expected from compression and shearing
of the regular magnetic field; this could be the result of decoupling
of the regular field from the dense molecular clouds. The regular field
in the ridge is probably strong enough to
reduce significantly shear in the diffuse gas (to which it is coupled)
and hence to reduce magnetic field amplification by shearing.
This contributes to the misalignment of the observed field orientation
with respect to the velocity vectors of the dense gas.
Our observations, for the first time, indicate that
magnetic forces can control the
flow of the diffuse interstellar gas at kiloparsec scales.
The total radio intensity reaches its maximum in the circumnuclear starburst
regions, where the equipartition field strength is about
,
amongst the strongest fields detected in spiral galaxies so far. The regular field in
the inner region has a spiral shape with large pitch angle,
indicating the action of a dynamo. Magnetic stress leads to mass
inflow towards the centre, sufficient to feed the active nucleus
in NGC 1097. –
We detected diffuse X-ray emission, possibly forming a
halo of hot gas around NGC 1097.
Key words: galaxies: magnetic fields / galaxies: individual: NGC 1097, NGC 1365 / galaxies: spiral / galaxies: structure / ISM: magnetic fields / galaxies: nuclei
© ESO, 2005
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