Despite the detection of hundreds of fast radio bursts (FRBs) to date, their precise astrophysical origins remain uncertain. Observations have revealed them to be energetic, millisecond-duration radio transients, with high inferred brightness temperatures implying coherent non-thermal emission, short duration implying a small emitting region, and typically high linear polarization degree implying strong, ordered magnetic fields. Alongside studies of FRB properties, about 100 FRBs have been localized with a precision of a few arcsec or better which allow for robust association to their host galaxies. At the most basic level, this has enabled constraints on their global host stellar populations and thus inference on both the conditions under which FRB progenitors form and how they trace galaxy properties.

Gordon et al. present deep optical and near-infrared observations of the host galaxies of 34 fast radio bursts (FRBs) detected by the Commensal Real-time ASKAP Fast Transient (CRAFT) survey to compare the locations of FRBs relative to their host light distributions. They model their host surface brightness profiles and calculate the likelihood the observed allocation of each FRB is consistent with (i) the smooth light of its host galaxy, (ii) residual (primarily spiral) substructure, or (iii) globular cluster distributions. The majority of FRBs favour locations within the disks of their galaxies, while only 7~13% favour a globular cluster origin. At redshifts z < 0.15, where spiral structure is apparent in 86% of the sample of FRB hosts, the team find 20~46% of FRBs favour an association with spiral arms. However, this moderate fraction of FRBs associated with spiral structure indicates that high star formation efficiency of the youngest and most massive stars is not a predominant driver in the production of FRB progenitors.

The image above shows imaging and the light profiles considered for FRB 20240312D along with the FRB position. The host galaxy for this FRB has a multi-arm spiral morphology. The smaller panels represent the Galfit surface brightness profile model (“Profile”), residual image (“Residual”), and 2D synthetic globular cluster distribution models (“GC Ellipsoidal”; “GC Spherical”). The preferred model for the FRB is denoted with a white check-mark. The images are oriented with North up and East to the left and span 1 arcminute on a side.