AMI limits on 15 GHz excess emission in northern HII regions.pdf

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AMI limits on 15 GHz excess emission in northern HII regions.pdf

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AMI limits on 15 GHz excess emission in northern HII regions

a r X i v : 0 7 1 1 .3 1 2 0 v 1 [ a s t r o - p h ] 2 0 N o v 2 0 0 7 Mon. Not. R. Astron. Soc. 000, 1–16 (2005) Printed 2 February 2008 (MN LATEX style file v2.2) AMI limits on 15GHz excess emission in northern Hii regions AMI CONSORTIUM: Scaife A. M. M.?, Hurley-Walker N., Davies, M. L., Duffett-Smith, P. J., Feroz, F., Grainge K. J. B., Green D. A., Hobson M. P., Kaneko, T., Lasenby, A. N., Pooley G. G., Saunders R. D. E., Scott P. F., Titterington D. J., Waldram E. M., Zwart J. Astrophysics Group, Cavendish Laboratory, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK. Accepted —; received —; in original form 2 February 2008 ABSTRACT We present observations between 14.2 and 17.9GHz of sixteen Galactic Hii regions made with the Arcminute Microkelvin Imager (AMI). In conjunction with data from the literature at lower radio frequencies we investigate the possibility of a spinning dust component in the spectra of these objects. We conclude that there is no significant evidence for spinning dust towards these sources and measure an average spectral index of α = 0.15± 0.07 (where S ∝ ν?α) between 1.4 and 17.9GHz for the sample. Key words: ISM:Hii regions – radio continuum:ISM – ISM:clouds – radiation mech- anisms:thermal 1 INTRODUCTION Recent observations of Galactic targets (Finkbeiner et al. 2002; 2004; Casassus et al. 2004;2006; Watson et al. 2005; Scaife et al. 2006; Dickinson et al. 2007) have provided some evidence for the anomalous microwave emission commonly ascribed to spinning dust (Drain Lazarian 1998a,b). This emission was first seen as a large scale phenomenon in CMB observations and represented a problem as it emits in the frequency range 10–60GHz (Kogut et al. 1996; Leitch et al. 1997; de Oliviera-Costa et al. 2002; 2004) close to the minimum of the combined synchrotron, Bremsstrahlung and thermal dust emissions at 70GHz. Indeed the models of Draine Lazarian predict a spectrum for spinning dust which is strongly peaked between 20 and 40GHz. Aris