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Starburst activity in a ROSAT narrow emission-line galaxy |
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| Authors: | Katherine F Gunn I M MHardy O Almaini T Shanks T J Sumner T W B Muxlow A Efstathiou L R Jones S M Croom J C Manners A M Newsam K O Mason S B G Serjeant M Rowan-Robinson |
| Institution: | Department of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ;Institute for Astronomy, The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ;Department of Physics, University of Durham, South Road, Durham DH1 3LE;Imperial College of Science, Technology and Medicine, Blackett Laboratory, Prince Consort Road, London SW7 2BZ;University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire SK11 9DL;School of Physics and Astronomy, University of Birmingham Edgbaston, Birmingham B15 2TT;Anglo-Australian Observatory, PO Box 296, Epping, NSW 2121, Australia;Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD;Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT |
| Abstract: | We present multiwaveband photometric and optical spectropolarimetric observations of the R =15.9 narrow emission-line galaxy R117_A which lies on the edge of the error circle of the ROSAT X-ray source R117. The overall spectral energy distribution of the galaxy is well modelled by a combination of a normal spiral galaxy and a moderate-strength burst of star formation. The far-infrared and radio emission is extended along the major axis of the galaxy, indicating an extended starburst. On positional grounds, the galaxy is a good candidate for the identification of R117, and the observed X-ray flux is very close to what would be expected from a starburst of the observed far-infrared and radio fluxes. Although an obscured high-redshift QSO cannot be entirely ruled out as contributing some fraction of the X-ray flux, we find no candidates to K =20.8 within the X-ray error box, and so conclude that R117_A is responsible for a large fraction, if not all, of the X-ray emission from R117. Searches for indicators of an obscured AGN in R117_A have so far proven negative; deep spectropolarimetric observations show no signs of broad lines to a limit of 1 per cent and, for the observed far-infrared and radio emission, we would expect 10 times greater X-ray flux if the overall emission were powered by an AGN. We therefore conclude that the X-ray emission from R117 is dominated by starburst emission from the galaxy R117_A. |
| Keywords: | galaxies: individual: R117_A galaxies: starburst X-rays: galaxies |