A Sino-German λ6 cm polarisation survey of the Galactic plane

VIII. Small-diameter sources^{⋆,⋆⋆,⋆⋆⋆}

¹ Max-Planck-Institut für Radioastronomie, auf dem Hügel 69, 53121 Bonn, Germany
e-mail: wreich@mpifr-bonn.mpg.de
² National Astronomical Observatories, CAS, Jia-20 Datun Road, Chaoyang District, 100012 Beijing, PR China
³ Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006, Australia

Received: 20 September 2013
Accepted: 23 October 2013

Abstract

Aims. Information of small-diameter sources is extracted from the Sino-German λ6 cm polarisation survey of the Galactic plane carried out with the Urumqi 25-m telescope.

Methods. We performed two-dimensional elliptical Gaussian fits to the λ6 cm maps to obtain a list of sources with total-intensity and polarised flux densities.

Results. The source list contains 3832 sources with a fitted diameter smaller than 16′ and a peak flux density exceeding 30 mJy, so about 5× the rms noise, of the total-intensity data. The cumulative source count indicates completeness for flux densities exceeding about 60 mJy. We identify 125 linearly polarised sources at λ6 cm with a peak polarisation flux density greater than 10 mJy, so about 3× the rms noise of the polarised-intensity data.

Conclusions. Despite lacking compact steep spectrum sources, the λ6 cm catalogue lists about 20% more sources than the Effelsberg λ21 cm source catalogue at the same angular resolution and for the same area. Most of the faint λ6 cm sources must have a flat spectrum and are either H   ii regions or extragalactic. When compared with the Green Bank λ6 cm (GB6) catalogue, we obtain higher flux densities for a number of extended sources with complex structures. Polarised λ6 cm sources density are uniformly distributed in Galactic latitude. Their number density decreases towards the inner Galaxy. More than 80% of the polarised sources are most likely extragalactic. With a few exceptions, the sources have a higher percentage polarisation at λ6 cm than at λ21 cm. Depolarisation seems to occur mostly within the sources with a minor contribution from the Galactic foreground emission.