Towards a free–free template for CMB foregrounds

By C. Dickinson, R. Davies, R. Observatory, U.K.. 2003

181 citations recorded by the source corpus.

A full-sky template map of the Galactic free-free foreground emission component is increasingly important for high sensitivity CMB experiments. We use the recently published Hα data of both the northern and southern skies as the basis for such a template. The first step is to correct the Hα maps for dust absorption using the 100 � m dust maps of Schlegel, Finkbeiner & Davis (1998). We show that for a range of longitudes, the Galactic latitude distribution of absorption suggests that it is 33 per cent of the full extragalactic absorption. A reliable absorption-corrected Hα map can be produced for � 95 per cent of the sky; the area for which a template cannot be recovered is the Galactic plane area |b| < 5 ◦ , l = 260 ◦ 0 ◦ 160 ◦ and some isolated dense dust clouds at intermediate latitudes. The second step is to convert the dust-corrected Hα data into a predicted radio surface brightness. The free-free emission formula is revised to give an accurate expression (1 per cent) for the radio emission covering the frequency range 100 MHz to 100 GHz and the electron temperature range 3000 to 20000 K. The main uncertainty when applying this expression is the variation of electron temperature across the sky. The emission formula is verified in several extended Hii regions using data in the range 408 to 2326 MHz. A full-sky free-free template map is presented at 30 GHz; the scaling to other frequencies is given. The Haslam et al. all-sky 408 MHz map of the sky can be corrected for this free-free component, which amounts to a � 6 per cent correction at intermediate and high latitudes, to provide a pure synchrotron all-sky template. The implications for CMB experiments are discussed.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/f41376d5a76c66c13610d0a589c1d881a60532e0

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Citations in the corpus

H i intensity mapping: a single dish approach (2012, methodology): “The EM can be estimated using Hα measurements, which can then be converted to radio brightness temperature assuming Te is known and the dust absorption is small (Dickinson et al. 2003).”
Component separation methods for the PLANCK mission (2008, background): “Free-free emission is based on the model of Dickinson et al. (2003) assuming an electronic temperature of 7000 K.”
Separation of anomalous and synchrotron emissions using WMAP polarization data (2008, methodology): “It is important to point out that the free-free spectral index is a slowly varying function of frequency and electron temperature (Bennett et al., 1992; Dickinson et al., 2003; Bennett et al., 2003b): βff = 2 + 1 10.48 + 1.5 ln(Te/8000K)− ln(νGHz) .”
DEVELOPMENT OF THE MODEL OF GALACTIC INTERSTELLAR EMISSION FOR STANDARD POINT-SOURCE ANALYSIS OF FERMI LARGE AREA TELESCOPE DATA (2016, background): “The Hα emission, a two-particle process proportional to the integral of the square of the electron density along the line of sight, suffers from dust absorption at low latitudes (Dickinson et al. 2003) and from scattering by interstellar dust (Witt et al. 2010; Seon & Witt 2012).”
STAR FORMATION IN MASSIVE CLUSTERS VIA THE WILKINSON MICROWAVE ANISOTROPY PROBE AND THE SPITZER GLIMPSE SURVEY (2009, background): “MICROWAVE DATA AND WMAP The only wavelength range in which free-free dominates the emission from the Galactic plane is in the microwave, between 10 and 100 GHz, placing this in the center of the frequency range of cosmic microwave background (CMB) experiments (Dickinson et al. 2003).”
The global dust SED: tracing the nature and evolution of dust with DustEM (2010, methodology): “The free-free contribution to the emission was subtracted using the model of Dickinson et al. (2003).”
The pre-launch Planck Sky Model: a model of sky emission at submillimetre to centimetre wavelengths (2012, methodology): “The free-free template is obtained from the WMAP MEM map, complemented with the Hα all-sky template by Finkbeiner (2003) corrected for extinction as in Dickinson et al. (2003).”
Radio observational constraints on Galactic 3D-emission models (2007, methodology): “Hα observations need an extinction correction to be a reliable free-free emission template (Dickinson et al. 2003), which is, however, only possible out of the plane.”
An improved source-subtracted and destriped 408 MHz all-sky map (2014, methodology): “…each of the 5 WMAP frequency maps is fitted simultaneously with a constant offset and three external templates, namely the 408 MHz survey, the Dickinson et al. (2003) (DDD) Hα survey, and the Finkbeiner et al. (1999) (FDS8) 94 GHz map, corresponding respectively to tracers c© 2002 RAS, MNRAS…”
Planck intermediate results. XXII. Frequency dependence of thermal emission from Galactic dust in intensity and polarization (2014, methodology): “The mean dust SED derived using the three-template fit depends on the correction of the DDD Hα map for dust scattering and extinction (Dickinson et al. 2003; Witt et al. 2010; Brandt & Draine 2012; Bennett et al. 2013).”
The interstellar cosmic-ray electron spectrum from synchrotron radiation and direct measurements. (2011, background): “…do not use their results here. contribution even at 1420 MHz is then small (Reich & Reich 1988b; Broadbent et al. 1989), a recent estimate being 15% (Dickinson et al. 2003), and less at lower frequencies (while at WMAP frequencies our maps separate out the non-thermal component as explained above).”
NINE-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) OBSERVATIONS: FINAL MAPS AND RESULTS (2012, background): “Free-free differences for the Gum away from the plane, where the optical depth is < 1, can be explained by a low electron temperature for this region (Dickinson et al. 2003; Woermann et al. 2000).”