The QUaD galactic plane survey. I. Maps and analysis of diffuse emission

Abstract

We present a survey of ~800 deg^2 of the galactic plane observed with the QUaD telescope. The primary products of the survey are maps of Stokes I, Q, and U parameters at 100 and 150 GHz, with spatial resolution of 5' and 3'.5, respectively. Two regions are covered, spanning approximately 245°–295° and 315°–5° in the galactic longitude l and −4° < b < +4° in the galactic latitude b. At 0°.02 square pixel size, the median sensitivity is 74 and 107 kJy sr^(−1) at 100 GHz and 150 GHz respectively in I, and 98 and 120 kJy sr^(−1) for Q and U. In total intensity, we find an average spectral index of α = 2.35 ± 0.01 (stat) ± 0.02 (sys) for |b| ≤ 1°, indicative of emission components other than thermal dust. A comparison to published dust, synchrotron, and free–free models implies an excess of emission in the 100 GHz QUaD band, while better agreement is found at 150 GHz. A smaller excess is observed when comparing QUaD 100 GHz data to the WMAP five-year W band; in this case, the excess is likely due to the wider bandwidth of QUaD. Combining the QUaD and WMAP data, a two-component spectral fit to the inner galactic plane (|b| ≤ 1°) yields mean spectral indices of α_s = −0.32 ± 0.03 and α_d = 2.84 ± 0.03; the former is interpreted as a combination of the spectral indices of synchrotron, free–free, and dust, while the second is largely attributed to the thermal dust continuum. In the same galactic latitude range, the polarization data show a high degree of alignment perpendicular to the expected galactic magnetic field direction, and exhibit mean polarization fraction 1.38 ± 0.08 (stat) ± 0.1 (sys)% at 100 GHz and 1.70 ± 0.06 (stat) ± 0.1 (sys)% at 150 GHz. We find agreement in polarization fraction between QUaD 100 GHz and the WMAP W band, the latter giving 1.1% ± 0.4%.