Searching for anomalous microwave emission in nearby galaxies. K-band observations with the Sardinia Radio Telescope

Abstract

<BR /> Aims: 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 anomalous microwave emission (AME), a radiation component presumably due to spinning dust grains, which has been observed thus far in the Milky Way and only in a handful of other galaxies (most notably, M 31). <BR /> Methods: 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. <BR /> Results: We only found upper limits for AME. These nondetections, and other upper limits in the literature, are nevertheless consistent with the average AME emissivity from a few detections: it is ϵ<SUB>30 GHz</SUB><SUP>AME</SUP> = 2.4 ± 0.4 × 10<SUP>−2</SUP> MJy sr<SUP>−1</SUP> (M<SUB>⊙</SUB> pc<SUP>−2</SUP>)<SUP>−1</SUP> in units of dust surface density (equivalently, 1.4 ± 0.2 × 10<SUP>−18</SUP> Jy sr<SUP>−1</SUP> (H cm<SUP>−2</SUP>)<SUP>−1</SUP> in units of H column density). We finally suggest searching for AME in quiescent spirals with relatively low radio luminosity, such as M 31.