Searching for Anomalous Microwave Emission in nearby galaxies. K-band observations with the Sardinia Radio Telescope

Abstract

We observed four nearby spiral galaxies (NGC 3627, NGC 4254, NGC 4736 and NGC 5055) in the K band with the 64-m Sardinia Radio Telescope, with the aim of detecting the Anomalous Microwave Emission (AME), a radiation component presumably due to spinning dust grains, observed so far in the Milky Way and in a handful of other galaxies only (most notably, M 31). We mapped the galaxies at 18.6 and 24.6 GHz and studied their global photometry together with other radio-continuum data from the literature, in order to find AME as emission in excess of the synchrotron and thermal components. We only find upper limits for AME. These non-detections, and other upper limits in the literature, are nevertheless consistent with the average AME emissivity from the few detections: it is $\hat{I}{\mu }_{30\mathrm{GHz}}^{\mathrm{AME}}=2.4\pm 0.4\times 10^{-2}$ MJy sr${}^{-1}$ (M${}_{\odot }$ pc${}^{-2}$)${}^{-1}$ in units of dust surface density (equivalently, $1.4\pm 0.2\times 10^{-18}$ Jy sr${}^{-1}$ (H cm${}^{-2}$)${}^{-1}$ in units of H column density). We finally suggest to search for AME in quiescent spirals with relatively low radio luminosity, such as M~31.

A&A Letter, accepted