A Caltech Library Service

A determination of the spectra of Galactic components observed by the Wilkinson Microwave Anisotropy Probe

Davies, R. D. and Dickinson, C. and Banday, A. J. and Jaffe, T. R. and Górski, K. M. and Davis, R. J. (2006) A determination of the spectra of Galactic components observed by the Wilkinson Microwave Anisotropy Probe. Monthly Notices of the Royal Astronomical Society, 370 (3). pp. 1125-1139. ISSN 0035-8711.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


Wilkinson Microwave Anisotropy Probe (WMAP) data when combined with ancillary data on free-free, synchrotron and dust allow an improved understanding of the spectrum of emission from each of these components. Here, we examine the sky variation at intermediate latitudes using a cross-correlation technique. In particular, we compare the observed emission in 15 selected sky regions to three 'standard' templates. The free-free emission of the diffuse ionized gas is fitted by a well-known spectrum at K and Ka band, but the derived emissivity corresponds to a mean electron temperature of similar to 4000-5000 K. This is inconsistent with estimates from Galactic H II regions although a variation in the derived ratio of H alpha to free-free intensity by a factor of similar to 2 is also found from region to region. The origin of the discrepancy is unclear. The anomalous emission associated with dust is clearly detected in most of the 15 fields studied. The anomalous emission correlates well with the Finkbeiner, Davis & Schlegel model 8 predictions (FDS8) at 94 GHz, with an effective spectral index between 20 and 60 GHz, of beta similar to -2.85. Furthermore, the emissivity varies by a factor of similar to 2 from cloud to cloud. A modestly improved fit to the anomalous dust at K band is provided by modulating the template by an estimate of the dust colour temperature, specifically FDS8 x T^n. We find a preferred value n similar to 1.6, although there is a scatter from region to region. Nevertheless, the preferred index drops to zero at higher frequencies where the thermal dust emission dominates. The synchrotron emission steepens between GHz frequencies and the WMAP bands. There are indications of spectral index variations across the sky but the current data are not precise enough to accurately quantify this from region to region. Our analysis of the WMAP data indicates strongly that the dust-correlated emission at the low WMAP frequencies has a spectrum which is compatible with spinning dust; we find no evidence for a synchrotron component correlated with dust. The importance of these results for the correction of cosmic microwave background data for Galactic foreground emission is discussed.

Item Type:Article
Related URLs:
URLURL TypeDescription
Dickinson, C.0000-0002-0045-442X
Additional Information:© 2006 The Authors. Journal compilation © 2006 RAS. Accepted 2006 May 11. Received 2006 May 9; in original form 2005 October 26. CD warmly thanks Barbara and Stanley Rawn Jr for funding a research scholarship at the California Institute of Technology. We thank an anonymous referee for useful comments, which led to significant improvements in this paper. Some of the results in this paper have been derived using the HEALPIX package (Górski et al. 2005). We acknowledge the use of the LAMBDA. Support for the LAMBDA is provided by the NASA Office of Space Science. The WHAM is funded by the National Science Foundation. We thank Bruce Draine for making his spinning dust models available.
Funding AgencyGrant Number
Barbara and Stanley Rawn, Jr.UNSPECIFIED
National Science FoundationUNSPECIFIED
Subject Keywords:radiation mechanisms: general; cosmic microwave background; cosmology: observations; diffuse radiation; radio continuum: ISM
Issue or Number:3
Record Number:CaltechAUTHORS:DAVmnras06a
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12395
Deposited By: Tony Diaz
Deposited On:11 Dec 2008 04:45
Last Modified:09 Mar 2020 13:18

Repository Staff Only: item control page