A derivation of the free–free emission on the Galactic plane between ℓ= 20° and 44°

Authors

  • Marta I. R. Alves,

    Corresponding author
    1. Institut d’Astrophysique Spatiale, CNRS (8617) Université Paris-Sud 11, Bâtiment 121, Orsay, 91405 France
    2. Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL
      E-mail: marta.alves@ias.u-psud.fr
    Search for more papers by this author
  • Rodney D. Davies,

    1. Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL
    Search for more papers by this author
  • Clive Dickinson,

    1. Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL
    Search for more papers by this author
  • Mark Calabretta,

    1. Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia
    Search for more papers by this author
  • Richard Davis,

    1. Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL
    Search for more papers by this author
  • Lister Staveley-Smith

    1. International Centre for Radio Astronomy Research, M468, University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia
    Search for more papers by this author

E-mail: marta.alves@ias.u-psud.fr

ABSTRACT

We present the derivation of the free–free emission on the Galactic plane between ℓ= 20° and 44° and |b|≤ 4°, using radio recombination line (RRL) data from the H i Parkes All Sky Survey (HIPASS). Following an upgrade of the RRL data reduction technique, which improves significantly the quality of the final RRL spectra, we have extended the analysis to three times the area covered in Alves et al. The final RRL map has an angular resolution of 14.8 arcmin and a velocity resolution of 20 km s−1.

The electron temperature (Te) distribution of the ionized gas in the area under study at 1.4 GHz is derived using the line and continuum data from the present survey. The mean Te on the Galactic plane is 6000 K. The first direct measure of the free–free emission is obtained based on the derived Te distribution. Subtraction of this thermal component from the total continuum leads to the first direct measurement of the synchrotron emission at 1.4 GHz. A narrow component of width 2° is identified in the latitude distribution of the synchrotron emission. We present a list of H ii regions and supernova remnants (SNRs) extracted from the present free–free and synchrotron maps, where we confirm the synchrotron nature of the SNRs G42.0−0.1 and G41.5+0.4 proposed by Kaplan et al. and the SNR G35.6−0.4 recently re-identified by Green.

The latitude distribution for the RRL-derived free–free emission shows that the Wilkinson Microwave Anisotropy Probe (WMAP) maximum entropy method is too high by ∼50 per cent, in agreement with other recent results. The extension of this study to the inner Galaxy region ℓ=−50° to 50° will allow a better overall comparison of the RRL result with WMAP.

Ancillary