QUIJOTE scientific results - VI. The Haze as seen by QUIJOTE

A B S T R A C T The Haze is an excess of microwave intensity emission surrounding the Galactic Centre. It is spatially correlated with the y-ray Fermi bubbles, and with the S-PASS radio polarization plumes, suggesting a possible common pro v enance. The models proposed to explain the origin of the Haze, including energetic events at the Galactic Centre and dark matter decay in the Galactic halo, do not yet provide a clear physical interpretation. In this paper, we present a reanalysis of the Haze including new observations from the Multi-Frequency Instrument (MFI) of the Q-U-I Joint TEnerife (QUIJOTE) experiment, at 11 and 13 GHz. We analyse the Haze in intensity and polarization, characterizing its spectrum. We detect an excess of diffuse intensity signal ascribed to the Haze. The spectrum at frequencies 11 GHz < v < 70 GHz is a power law with spectral index beta(H) = -2.79 +/- 0.08, which is flatter than the Galactic synchrotron in the same region ( beta(S) = -2.98 +/- 0.04), but steeper than that obtained from previous works ( beta(H) similar to -2.5 at 23 GHz < v < 70 GHz). We also observe an excess of polarized signal in the QUIJOTE-MFI maps in the Haze area. This is a first hint detection of polarized Haze, or a consequence of curvature of the synchrotron spectrum in that area. Finally, we show that the spectrum of polarized structures associated with Galactic Centre activity is steep at low frequencies ( beta similar to -3.2 at 2.3 GHz < v < 23 GHz), and becomes flatter abo v e 11 GHz.

Automated summary

This paper presents a reanalysis of the Haze, including new observations from the Multi-Frequency Instrument (MFI) of the Q-U-I Joint TEnerife (QUIJOTE) experiment. An excess of diffuse intensity signal and polarized signal in the Haze area are detected, and their spectra are characterized. The results reveal differences in the spectrum of the Haze compared to Galactic synchrotron and the presence of polarized structures associated with Galactic Centre activity.