The G305 star-forming complex: a wide-area radio survey of ultracompact H ii regions

Authors

  • L. Hindson,

    Corresponding author
    1. Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, College Lane, Hatfield AL10 9AB
    2. ATNF, CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
    Search for more papers by this author
  • M. A. Thompson,

    1. Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, College Lane, Hatfield AL10 9AB
    Search for more papers by this author
  • J. S. Urquhart,

    1. ATNF, CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
    2. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
    Search for more papers by this author
  • A. Faimali,

    1. Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, College Lane, Hatfield AL10 9AB
    Search for more papers by this author
  • J. S. Clark,

    1. Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA
    Search for more papers by this author
  • B. Davies

    1. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
    2. School of Physics and Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT
    Search for more papers by this author

E-mail: l.hindson@herts.ac.uk

ABSTRACT

We present wide-area radio continuum 5.5 and 8.8 GHz (5.5 and 3.4 cm) Australia Telescope Compact Array observations of the complex and rich massive star-forming region G305. The aim of this study is to perform an un-targeted survey of the region in search of the compact radio emission associated with ultracompact (UC) H ii regions. Observations presented here encompass the entire complex and have a maximum resolution of ∼ 1.5 × 1.4  arcsec and sensitivity of ∼0.07 mJy beam−1. By applying a data reduction method that emphasizes small-scale structure, we are able to detect 71 compact radio sources distributed throughout the observed field. To explore the nature of these compact radio sources we compare to mid-infrared data and in this way identify 56 background sources, eight stellar radio sources, a single bright-rimmed cloud and six candidate UC H ii regions. The physical properties of these candidate UC H ii regions are determined and reveal that five candidates have peak properties consistent with known UC H ii regions with source radii ranging from 0.04 to 0.1 pc, emission measures from 2.56 to 10.3 × 10−6 pc cm−6 and electron densities of 0.34–1.03 × 104 cm−3. We comment on these sites of recent massive star formation within G305 and by comparing to other star formation tracers (masers, NH3 and young stellar objects) build a picture of the star formation history of the region. Using these results we estimate a lower limit to the star formation rate for the region of ∼0.003 M yr−1.

Ancillary