The \^G Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. III. The Reddest Extended Sources in WISE

TL;DR

This study used WISE data to search for galaxies with extreme mid-infrared emission, aiming to identify potential signs of advanced extraterrestrial civilizations, but found no definitive evidence of such civilizations in the surveyed galaxies.

Contribution

It provides the largest MIR-based survey of galaxies for extraterrestrial civilizations, improves photometry calibration for extended sources, and identifies several intriguing sources for further investigation.

Findings

No galaxies host civilizations reprocessing >85% of starlight into MIR.

50 galaxies have MIR luminosities >50% reprocessing, consistent with star formation.

Five new sources with unusual MIR properties identified for follow-up.

Abstract

Nearby Type III (galaxy-spanning) Kardashev supercivilizations would have high mid-infrared (MIR) luminosities. We have used the Wide-field Infrared Survey Explorer (WISE) to survey ~$1 \times 10^5$ galaxies for extreme MIR emission, $10^3$ times more galaxies than the only previous such search. We have calibrated the WISE All-sky Catalog pipeline products to improve its photometry for extended sources. We present 563 extended sources with $|b| \ge 10$ and red MIR colors, having visually vetted them to remove artifacts. No galaxies in our sample host an alien civilization reprocessing more than 85% of its starlight into the MIR, and only 50 galaxies, including Arp 220, have MIR luminosities consistent with >50% reprocessing. Ninety of these (likely) extragalactic sources have little literature presence; in most cases they are likely barely resolved galaxies or pairs of galaxies undergoing large amounts of star formation. Five are new to science and deserve further study. The Be star 48 Librae sits within a MIR nebula, and we suggest that it may be creating dust. WISE, 2MASS, and Spitzer imagery shows that IRAS 04287+6444 is consistent with a previously unnoticed, heavily extinguished cluster of young stellar objects. We identify five "passive" (i.e. red) spiral galaxies with unusually high MIR and low NUV luminosity. We search a set of optically "dark" HI galaxies for MIR emission, and find none. These 90 poorly understood sources and five anomalous passive spirals deserve follow-up via both SETI and conventional astrophysics.