Statistical association between the candidate repeating FRB 20200320A and a galaxy group

Abstract

We present results from angular cross-correlations between select samples of CHIME/FRB repeaters and galaxies in three photometric galaxy surveys, which have shown correlations with the first CHIME/FRB catalog containing repeating and nonrepeating sources: WISE\(\times\)SCOS, DESI-BGS, and DESI-LRG. We find a statistically significant correlation (\(p\)-value \(<0.001\), after accounting for look-elsewhere factors) between a sample of repeaters with extragalactic DM \(>395\) pc cm\(^{-3}\) and WISE\(\times\)SCOS galaxies with redshift \(z>0.275\). We demonstrate that the correlation arises surprisingly because of a statistical association between FRB 20200320A (extragalactic DM \(\approx550\) pc cm\(^{-3}\)) and a galaxy group in the same dark matter halo at redshift \(z\approx0.32\). Based on our results, we suggest incorporating galaxy group and cluster catalogs into direct host association pipelines for FRBs with \(\lesssim1'\) localization precision, effectively utilizing the two-point information to constrain FRB properties such as their redshift. In addition, we find marginal evidence for a negative correlation at 99.4% CL between a sample of repeating FRBs with baseband data (median extragalactic DM \(=354\) pc cm\(^{-3}\)) and DESI-LRG galaxies with redshift \(0.3\le z<0.45\), suggesting that the repeaters might be more prone than apparent nonrepeaters to propagation effects due to intervening free electrons over angular scales \(\sim0\mbox{\).\!\!^\circ\(}5\).