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

TL;DR

This study used the Sardinia Radio Telescope to search for anomalous microwave emission in four nearby galaxies but only obtained upper limits, suggesting the need for further targeted observations in low-luminosity spirals.

Contribution

First observational attempt to detect AME in multiple nearby galaxies at K-band frequencies, providing upper limits and insights into its emissivity and distribution.

Findings

No direct detection of AME in the observed galaxies.

Upper limits are consistent with known AME emissivity from the Milky Way.

Suggests focusing on quiescent, low-luminosity spirals like M31 for future searches.

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 $\epsilon^\mathrm{AME}_{\mathrm{30~GHz}} = 2.4\pm0.4 \times 10^{-2}$ MJy sr$^{-1}$ (M$_\odot$ pc$^{-2}$)$^{-1}$ in units of dust surface density (equivalently, $1.4\pm0.2 \times 10^{-18}$ 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.