Issue |
A&A
Volume 474, Number 2, November I 2007
|
|
---|---|---|
Page(s) | 415 - 429 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20077497 | |
Published online | 28 August 2007 |
Magnetic fields and gas in the cluster-influenced spiral galaxy NGC 4254*
I. Radio and X-rays observations
1
Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland e-mail: chris@oa.uj.edu.pl
2
XMM-Newton Science Operations Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
3
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Received:
16
March
2007
Accepted:
6
August
2007
Aims.Radio observations can show how cluster galaxies are affected by various environmental factors, that perturb their morphology, as well as modify properties of the interstellar medium (ISM), especially the characteristics of its magnetic field.
Methods.We made high-resolution and high-sensitivity radio-polarimetric VLA
observations of NGC 4254 at three frequencies (8.46, 4.86, and 1.43 GHz). The
interferometric data were extended with single-dish
(100-m Effelsberg) observations. Next we performed sensitive
XMM-Newton observations in X-rays and UV light to investigate the hot gas component and
its possible interaction with the hot cluster medium. For a complete picture of
the interplay between various gas phases, we also used optical, , and
infrared (Spitzer) data.
Results.The distribution of total radio intensity at 8.46 GHz and 4.86 GHz
reveals a global asymmetry with a more diffuse and almost two times
larger extension to the north than to the south. The radio-polarized intensity
is even more asymmetric, showing a strange bright ridge in the southern
disk edge, displaced to the downstream side of the local density wave. Magnetic
arms can also be seen in other disk portions, mostly (but not always) avoiding
nearby optical spiral arms. Spatially-resolved emission of hot X-ray gas from the
whole galactic disk, with its soft component closely tracing star-forming regions, is
detected. Various gas components of a thermal origin show strong wavelet
crosscorrelations (), but the polarized intensity anticorrelates
(
) with the thermal and X-ray emission. The slope of the local radio
nonthermal-infrared relation is <1, thus smaller than for the radio
thermal-infrared one (≥1). Using the radio thermal emission-based
star-formation rate (SFR), we find higher extinction in more Hα luminous
star-forming regions with a power-law slope of 0.83. The galaxy's estimated
mean SFR of
is
three times larger than in other spirals with a similar Hubble type.
Conclusions.NGC 4254 seems to belong to the class of “young” Virgo cluster members, which recently experienced a gravitational encounter at the cluster's periphery, which in turn perturbed its spiral arms by tidal forces and triggered a burst of star formation that still maintains strong radio and infrared emissions. Tidal forces could also shear the magnetic field in the southern disk portion and lead to the observed polarized ridge, although magnetic field compression by weak ram pressure forces of the cluster gas cannot be excluded. The case of NGC 4254 shows that the polarized signal provides additional information on the MHD processes acting on magnetized plasma during the galaxy's evolution, which cannot be obtained from any other ISM component.
Key words: galaxies: general / galaxies: ISM / galaxies: magnetic fields / galaxies: interactions / radio continuum: galaxies / ISM: magnetic fields
© ESO, 2007
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