The dependence of the IR-radio correlation on the metallicity

TL;DR

This study examines how the IR-radio correlation varies with metallicity in galaxies, revealing that metal-poor galaxies have lower IR-to-radio ratios, especially at longer IR wavelengths, due to dust temperature and obscured star formation effects.

Contribution

It provides the first detailed analysis of the metallicity dependence of the IR-radio correlation across multiple IR bands, proposing a new mechanism involving dust temperature and obscured star formation.

Findings

Metal-poor galaxies have lower qIR than metal-rich ones, especially at longer IR wavelengths.

qIR correlates positively with metallicity and IR-to-FUV ratio, negatively with IR color.

Total SFR/radio ratio remains consistent across metallicities, confirming radio as an SFR tracer.

Abstract

We have compiled a sample of 26 metal-poor galaxies with 12 + log(O/H) < 8.1 with both infrared continuum and 1.4 GHz radio continuum data. By comparing to galaxies at higher metallicity, we have investigated the dependence on the metallicity of the IR-radio relationship at 24 um, 70 um, 100 um and 160 um bands as well as the integrated FIR luminosity. It is found that metal-poor galaxies have on average lower qIR than metal-rich ones with larger offsets at longer IR wavelengths, from -0.06 dex in q24um to -0.6 dex in q160um. The qIR of all galaxies as a whole at 160 um show positive trends with the metallicity and IR-to-FUV ratio, and negative trends with the IR color, while those at lower IR wavelengths show weaker correlations. We proposed a mechanism that invokes combined effects of low obscured-SFR/total-SFR fraction and warm dust temperature at low metallicity to interpret the above behavior of qIR, with the former reducing the IR radiation and the latter further reducing the IR emission at longer IR wavelength. Other mechanisms that are related to the radio emission including the enhanced magnetic field strength and increased thermal radio contribution are unable to reconcile the IR-wavelength-dependent differences of qIR between metal-poor and metal- rich galaxies. In contrast to qIR, the mean total-SFR/radio ratio of metal-poor galaxies is the same as the metal-rich one, indicating the 1.4 GHz radio emission is still an effective tracer of SFRs at low metallicity.