ARCADE 2 Observations of Galactic Radio Emission

TL;DR

This paper uses ARCADE 2 data to model Galactic radio emission across multiple frequencies, confirming the presence of spinning dust and refining emission estimates at high latitudes.

Contribution

It provides the first detailed modeling of Galactic emission at 3-10 GHz using ARCADE 2 data, including evidence for spinning dust contribution.

Findings

Galactic emission spectral index beta = -2.55 +/- 0.03

Free-free emission contributes 0.10 +/- 0.01 at 3.15 GHz

Spinning dust accounts for 0.4 +/- 0.1 of emission at 22 GHz

Abstract

We use absolutely calibrated data from the ARCADE 2 flight in July 2006 to model Galactic emission at frequencies 3, 8, and 10 GHz. The spatial structure in the data is consistent with a superposition of free-free and synchrotron emission. Emission with spatial morphology traced by the Haslam 408 MHz survey has spectral index beta_synch = -2.5 +/- 0.1, with free-free emission contributing 0.10 +/- 0.01 of the total Galactic plane emission in the lowest ARCADE 2 band at 3.15 GHz. We estimate the total Galactic emission toward the polar caps using either a simple plane-parallel model with csc|b| dependence or a model of high-latitude radio emission traced by the COBE/FIRAS map of CII emission. Both methods are consistent with a single power-law over the frequency range 22 MHz to 10 GHz, with total Galactic emission towards the north polar cap T_Gal = 0.498 +/- 0.028 K and spectral index beta = -2.55 +/- 0.03 at reference frequency 1 GHz. The well calibrated ARCADE 2 maps provide a new test for spinning dust emission, based on the integrated intensity of emission from the Galactic plane instead of cross-correlations with the thermal dust spatial morphology. The Galactic plane intensity measured by ARCADE 2 is fainter than predicted by models without spinning dust, and is consistent with spinning dust contributing 0.4 +/- 0.1 of the Galactic plane emission at 22 GHz.