The application of the Mid-IR radio correlation to the $\hat{G}$ sample and the search for advanced extraterrestrial civilisations

TL;DR

This study applies the mid-IR radio correlation to a sample of sources to identify potential advanced extraterrestrial civilizations, finding most are consistent with natural astrophysical processes and very few could be artificial in origin.

Contribution

It demonstrates that the mid-IR radio correlation can effectively distinguish natural sources from potential Kardashev Type III civilizations in the $\

Findings

Most sources follow the mid-IR radio correlation, indicating natural astrophysical origins.

Identified 9 outliers with high $q_{22}$ values, mostly explainable by standard astrophysics.

Kardashev Type-III civilizations are likely very rare or absent in the local universe.

Abstract

Wright et al. 2014 have embarked on a search for advanced Karadashev Type III civilisations via the compilation of a sample of sources with extreme mid-IR emission and colours. In this scenario, the mid-IR emission is then primarily associated with waste heat energy by-products. I apply the Mid-IR radio correlation to this $\hat{G}$ sample (Griffith et al. 2015). I demonstrate that the mid-IR and radio luminosities are correlated for the sample with $q_{22}=1.35\pm0.42 $. By comparison, the First Look Survey (FLS) has $q_{22}=0.87\pm0.27$. The fact that the G-HAT sample largely follows the Mid-IR radio correlation, strongly suggests the vast majority of these sources are associated with galaxies in which natural astrophysical processes are dominant. This simple application of the mid-IR radio correlation can substantially reduce the number of false positives in the $\hat{G}$ catalogue, since galaxies occupied by advanced Kardashev Type III civilisations would be expected to exhibit very high values of $q$. Indeed I identify 9 outliers in the sample with $q_{22} > 2$ of which at least 3 have properties that are relatively well explained via standard astrophysical interpretations e.g. dust emission associated with nascent star formation and/or nuclear activity from a heavily obscured AGN. I also note that the comparison of resolved Mid-IR and radio images of galaxies on sub-galactic (kpc) scales can also be useful in identifying and recognising artificial mid-IR emission from less advanced intermediate Type II/III civilisations. Nevertheless, from the bulk properties of the $\hat{G}$ sample, I conclude that Kardashev Type-III civilisations are either very rare or do not exist in the local Universe.