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Cited by 165Astrophysics and Star Formation StudiesCosmology and Gravitation TheoriesAstrophysics and Cosmic Phenomena

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

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Davies, R. D., Dickinson, C., Banday, A. J., Jaffe, T. R., Górski, K. M., Davis, R. J.·2006·Monthly Notices of the Royal Astronomical Society
DOI 10.1111/j.1365-2966.2006.10572.x
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Abstract

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 ∼4000–5000 K. This is inconsistent with estimates from Galactic H ii regions although a variation in the derived ratio of Hα to free–free intensity by a factor of ∼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 β∼−2.85. Furthermore, the emissivity varies by a factor of ∼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 × Tn. We find a preferred value n∼ 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.

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  • The spectral index β for the Loop-I is about 3, indicating a cosmic-ray electron index of p about 3 at high latitudes.

    “It is found that the spectral index, β , (brightness temperature, Tb ∝ ν -β ) for the Loop-I is ≃ 3 (Finkbeiner 2004; Davies et al. 2006; Dobler & Finkbeiner 2008), indicating a CR electron index of p ≃ 3 at the high latitudes (following p = 2 β -3 for synchrotron emission).”

    From The Fermi/eROSITA bubbles: a look into the nuclear outflow from the Milky Way (2024) · cites this paper as Davies et al. 2006

    Table 5 and §4.5 report a synchrotron brightness-temperature index near −3 for a high-latitude region of the North Polar Spur, consistent with the citing sentence’s positive β under its ν^−β convention. Our copy does not identify that region as Loop-I, so it does not establish the Loop-I-specific attribution. The p ≃ 3 value is presented in the citing sentence as an inference from β, rather than a finding attributed to Davies et al. (LLM, conf=0.82)

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Research works printed but not linked: 4

  1. Casassus S., Readhead A. C. S., Pearson T. J., Nyman L. A., Shepherd M. C., Bronfman L., 2003, ApJ, 591, 556
  2. Fernández-Cerezo S. et al., 2006, MNRAS, in press (astro-ph/0601203) · arXiv
  3. Hansen F. K., Banday A. J., Eriksen H. K., Górski K. M., Lilje P. B., 2006, ApJ, submitted (astro-ph/0603308) · arXiv
  4. Leitch E. M., Readhead A. C. S., Pearson T. J., Myers S. T., 1997, ApJ, 486, L23

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Authors
Davies, R. D., Dickinson, C., Banday, A. J., Jaffe, T. R., Górski, K. M., & Davis, R. J.
Affiliations
  • University of Manchester (GB)
  • California Institute of Technology (US)
  • Max Planck Institute for Astrophysics (DE)
Corresponding author
  • Davies, R. D.
  • Dickinson, C.
  • Banday, A. J.
  • Jaffe, T. R.
ORCID
Venue
Monthly Notices of the Royal Astronomical Society
Publisher
Oxford University Press (OUP)
Published
2006-07-12
Volume
370
Issue
3
Pages
1125-1139
ISSN
0035-8711 (ISSN-L)
DOI
10.1111/j.1365-2966.2006.10572.x
OpenAlex
W2157421053
Cited by
165
References
53
Citations by year
2026: 1 · 2025: 4 · 2024: 5 · 2023: 6 · 2022: 5 · 2021: 1 · 2020: 7 · 2019: 28 · 2018: 5 · 2016: 10 · 2015: 17 · 2014: 7 · 2013: 11 · 2012: 13
FWCI
4.60
Type
journal article
Language
en
Open access
Locations
  • Monthly Notices of the Royal Astronomical Society (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • CaltechAUTHORS (California Institute of Technology) (submittedVersion)
  • CERN Document Server (European Organization for Nuclear Research) (submittedVersion)
  • Max Planck Institute for Plasma Physics (submittedVersion)
  • Max Planck Digital Library (submittedVersion)
  • MPG.PuRe (Max Planck Society) (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysics and Star Formation Studies
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Cosmology and Gravitation Theories
  • Physical Sciences › Physics and Astronomy › Nuclear and High Energy Physics › Astrophysics and Cosmic Phenomena
Keywords
Galactic foreground emission, free-free emission, synchrotron radiation, dust emission, spinning dust, spectral index, WMAP, cross correlation function, cosmic microwave background foregrounds, diffuse ionized gas, electron temperature, H-alpha emission

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