High-resolution radio continuum survey of M 33

Free access article

Issue		A&A Volume 472, Number 3, September IV 2007


Page(s)		785 - 796
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20077461

A&A 472, 785-796 (2007)
DOI: 10.1051/0004-6361:20077461

I. The radio maps

F. S. Tabatabaei, M. Krause, and R. Beck

Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: tabataba@mpifr-bonn.mpg.de

(Received 12 March 2007 / Accepted 25 May 2007)

Abstract
Aims.We study the exponential scale length of total radio emission, the spectral index distribution, and the linear radio polarization in the Scd galaxy M 33.
Methods.Observations were carried out using the 3.6 cm dual channel and the 6.2 cm four-channel receivers of the 100-m Effelsberg telescope along with the L-band VLA D-array at 20 cm.
Results.High spatial resolution and sensitivity in both total and linearly polarized radio continuum emission from M 33 were achieved. We found considerable extended emission, not only from the main arms I S and I N, but also from the weaker arms. The large-scale magnetic field exhibits well-ordered spiral structure with almost the same orientation as that of the optical spiral arms; however, it does not show a clear structural correlation or anti-correlation with the optical arms. There is a north-south asymmetry in polarization that is frequency-dependent. We found that the ring mean spectral index versus radius increases faster beyond R = 4 kpc. At each wavelength, the exponential scale length is larger inside than outside R = 4 kpc.
Conclusions.From the larger scale lengths at R < 4 kpc, we conclude that star-forming regions are mainly spread over the region R < 4 kpc without a dominant nuclear concentration. Furthermore, at R < 4 kpc, a spatial correlation between cosmic rays and star-forming regions may exist. From the behavior of the mean spectral indices obtained from different pairs of the radio continuum data at 3.6, 6.2, and 20 cm, we confirm that a decrease in the thermal fraction causes an increase in the spectral index. The frequency-dependent asymmetry in the polarization hints at asymmetry in Faraday depolarization.

Key words: galaxies: individual: M 33 -- radio continuum: galaxies -- galaxies: magnetic fields -- galaxies: ISM

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.