An investigation into correlations between FRB and host galaxy properties

TL;DR

This study investigates whether global host-galaxy properties influence FRB propagation effects, by examining correlations between FRB scattering, rotation measures, and polarisation with host metrics from a homogenised sample (CRAFT ICS plus literature). The authors combine high-time-resolution FRB pulse measurements with Prospector-derived galaxy properties and galfit structural parameters, applying robust statistical tests and bootstrapping to assess significance. They find strong correlations between the rest-frame scattering time and host compactness $M_*/(R_{\rm eff})^2$ as well as mass-weighted age $t_m$, and a weaker link with gas-phase metallicity $Z_{\rm gas}$; they also observe a strong anti-correlation between $|RM_{\rm ex}|$ and the disc axis ratio $b/a$, suggesting host geometry and magnetic fields contribute to RM. Polarisation results are largely inconclusive, with only weak, outlier-driven hints for circular polarisation; overall, the findings imply host environments can influence FRB observables but require larger samples and precise localisations to disentangle host vs progenitor contributions and to refine FRB mechanism models.

Abstract

Impulsive radio signals such as fast radio bursts (FRBs) are imprinted with the signatures of multi-path propagation through ionised media in the form of frequency-dependent temporal broadening of the pulse profile (scattering). The dominant source of scattering for most FRBs is expected to be within their host galaxies, an assumption which can be tested by examining potential correlations between properties of the FRBs and global properties of their hosts. Using results from the CRAFT survey, we investigate correlations across a range of host galaxy properties against attributes of the FRB that encode propagation effects: scattering timescale tau, polarisation fractions, and absolute Faraday rotation measure. From 21 host galaxy properties considered, we find three correlated with tau, including the stellar surface density (or compactness; Pearson p-value p = 0.002 and Spearman p = 0.010), mass-weighted age (Spearman p-value p = 0.009), and a weaker correlation with gas-phase metallicity (Spearman p = 0.017). Weakly significant correlations are also found with Halpha equivalent widths and gravitational potential. From 10,000 trials of reshuffled datasets, we expect 2 strong Spearman correlations only 2% of the time, and three weaker correlations in 6.6% of cases. Compact host galaxies may have more ionised content which scatters the FRB further. No correlation is seen with host galaxy inclination, which weakens the case for an inclination bias, as previously suggested for samples of localised FRBs. A strong (p = 0.002) correlation is found for absolute rotation measure with optical disc axis ratio b/a; greater rotation measures are seen for edge-on host galaxies. Further high-time resolution FRB detections, coupled with localisation and detailed follow-up on their host galaxies, are necessary to corroborate these initial findings and shed further light into the FRB mechanism.

Figures (6)

• Figure 1: Scatter plots for the logarithm of the rest-frame scattering time at a 1 GHz reference frequency with global galaxy properties: mass-weighted age, gas-phase metallicity, potential $M_{*}$/$R_{\rm eff}$, stellar surface density or compactness $M_{*}$/($R_{\rm eff}$)$^{2}$, $H\alpha$ EW, and optical galaxy inclination angle. Spearman and Pearson correlation coefficients, accompanied by p-values in square brackets and sample size, are in the upper-right legend.
• Figure 2: Continued. Two scatter plots for the logarithm of the rest-frame scattering time at a 1 GHz reference frequency with global galaxy properties: current-day stellar mass and SFR.
• Figure 3: Comparison of various global galaxy properties of FRB hosts with reliable scattering timescale measures. All points are coloured by the logarithm of the rest-frame scattering timescale at 1 GHz. Spearman and Pearson correlation results are given in the top left as in Fig ure \ref{['fig:taucorr']}. Top-left: mass-weighted age $t_{\rm m}$ versus compactness (or stellar surface density $M{*}$/($R_{\rm eff}$)$^{2}$). Top-right: mass-weighted age versus potential $M{*}$/$R_{\rm eff}$. No correlation is seen in either case for the properties compared in the top row. Bottom-left: gas-phase metallicity $\frac{Z_{\rm gas}}{Z_{\odot}}$ versus compactness. In this panel the size of the datapoints scales by a factor of 2$\times$($t_{\rm m}$)$^{3}$. Bottom-right: gas-phase metallicity with host galaxy mass-weighted stellar age. In this panel the size of the datapoints scales by a factor of 2$\times$($H\alpha$EW)$^{2}$. We see correlations for both these relations explored in the bottom row.
• Figure 4: Scatter plot and correlation tests for the rest-frame absolute $RM_{\rm ex}$ of 26 FRBs with the optical disc axis ratio b/a. Smaller values of b/a indicate a more edge-on disc relative to the plane of the sky. Such galaxies may have had the FRB pass through more of the galaxy en route to us and hence increase the rotation measure observed.
• Figure 5: Scatter plot and correlation tests for circular polarisation fraction of 27 FRBs with the logarithm of the effective radius of the host galaxy. If the lower-right datapoint is excluded (FRB 20230708), no significant negative correlation is found.