Millisecond Pulsars Modify the Radio-SFR Correlation

Abstract

The observed correlation between the far-infrared and radio luminosities of galaxies illustrates the close connection between star formation and cosmic-ray production. Intriguingly, recent LOFAR observations find a peculiar radio excess in galaxies with low star-formation rates and high stellar masses. We show that recycled/millisecond pulsars (MSPs) can dominate the nonthermal emission in these massive quiescent galaxies and explain the excess. This is in line with recent gamma-ray observation suggesting that MSPs may efficiently accelerate cosmic-ray electrons. We find that MSP-based models provide a significantly improved fit to the LOFAR data. We discuss implications for the radio and gamma-ray excesses in M31 and local electron and positron observations.

Snowmass2021 Cosmic Frontier White Paper: Puzzling Excesses in Dark Matter Searches and How to Resolve Them

“…Evidence of this process is found in mild evidence for TeV halos around MSPs in HAWC observations (e.g., Ref. [65]), correlation between radio luminosity and far-infrared observation in star-forming-galaxies [66], and highenergy tail of the GCE [67]. The e ± pairs injected by a putative MSPs population in the GC could produce detectable TeV-scale inverse-Compton (IC) emissions.…”