Millisecond Pulsars Modify the Radio-SFR Correlation in Quiescent Galaxies

TL;DR

Millisecond pulsars significantly influence the radio emission in quiescent galaxies, challenging the traditional link between star formation and radio luminosity, and explaining observed radio excesses in massive, low-star-formation galaxies.

Contribution

This study introduces a model where millisecond pulsars dominate radio emission in quiescent galaxies, providing a new perspective on the radio-FIR correlation and galaxy radio excesses.

Findings

MSPs can dominate radio emission in massive quiescent galaxies.

The MSP model better fits LOFAR radio observations.

Implications for cosmic-ray origin and galaxy evolution.

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 gamma-ray observations indicate that recycled/millisecond pulsars (MSPs), which do not trace recent star formation, may also efficiently accelerate cosmic-ray electrons. We study the contribution of MSPs to the galactic non-thermal radio emission, finding that they can dominate the emission from massive quiescent galaxies. This model can explain recent LOFAR observations that found a peculiar radio excess in galaxies with high stellar masses and low star-formation rates. We show that MSP-based models provide a significantly improved fit to LOFAR data. We discuss the implications for the radio-FIR correlation, the observation of radio excesses in nearby galaxies, and local electron and positron observations.