Low-frequency-selected Fast Radio Burst Host Galaxy Candidates

TL;DR

This work demonstrates that crossmatching CHIME/FRB baseband localisations with the low-frequency LoTSS DR2 catalog can identify plausible FRB host galaxies that are otherwise challenging to detect optically, including dust-obscured star-forming systems. By combining DM-based redshift constraints (via the Macquart relation) with multi-wavelength SED fitting and radio/Hα star-formation indicators, the study identifies two secure and one tentative host candidates, all consistent with ongoing star formation but with Hα-based SFRs suppressed by dust. The results show the promise of low-frequency radio data to complement optical host searches and hint at a richer diversity of FRB environments; they also outline limitations and biases, and point to upcoming data from LOFAR 2.0, LoTSS DR3, CHIME/FRB Outrigger, and CHORD for building a large, statistically robust FRB host sample. In the near term, this radio-based approach offers a practical path toward understanding FRB progenitors and their environments in a more dust-insensitive way, with the potential to reveal hosts that optical methods miss.

Abstract

We present a pilot study on the host galaxy environments of CHIME/FRBs by cross-matching baseband-localised events with the LOFAR Two-metre Sky Survey Data Release 2 (LoTSS DR2) at 144 MHz. Unlike traditional methods reliant on optical imaging, our radio-based selection allows for the identification of dust-obscured or optically faint star-forming galaxies. Of the 140 CHIME FRBs considered, 33 lie within the LoTSS DR2 footprint, and 16 show potential radio counterparts. Through multi-wavelength analysis, spectral energy distribution (SED) fitting, and redshift constraints from the Macquart relation, we identify two secure and one tentative host candidates, all consistent with active star formation. However, their H$α$-derived star formation rates appear underestimated, likely due to significant dust attenuation, as suggested by infrared colours and compact optical morphologies. Our results highlight the value of low-frequency radio data in complementing optical host searches and demonstrate the feasibility of host identification even in the absence of optical confirmation. With forthcoming data from LoTSS DR3 and the full CHIME/FRB baseband release, this method offers a promising path toward statistically robust studies of FRB host galaxies and their environments.

Figures (13)

• Figure 1: Sky distribution of 140 CHIME/FRB baseband-detected events (black circles) overlaid on the LoTSS DR2 survey footprint (shaded region). This figure illustrates which FRBs lie within the LoTSS coverage area based on the multi-order coverage (MOC) map. A total of 33 FRBs are found to fall within the footprint and are eligible for further cross-matching analysis.
• Figure 2: The correlation between FRB–radio-source separation and flux density for non-star objects in the LoTSS DR2 release. Coloured stars mark significant outliers from the random distribution, identified based on the KDE chance-alignment analysis and suggesting a higher likelihood of being the true host. Grey shade indicates density of matches to 15000 random points, and black contours, from the outermost to the innermost, represent the cumulative distributions of $\rm 99.9\%,\ 99\%,\ 95\%,\ 90\%,\ 75\%,\ and\ 50\%$ of the random points, respectively. Red points represent the matched FRBs, with error bars indicating the spatial extent of each radio galaxy.
• Figure 3: Optical and radio images of two secure candidates. Top panels: False-colour RGB images constructed from the $g$, $r$, and $z$ bands of the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys for two secure candidates. The white ellipses represent the $1\sigma$ and $2\sigma$ localisation uncertainty regions of the FRB, with the white cross marking the FRB centroid and the cyan cross indicating the position of the matched LoTSS radio source. Bottom panels: LoTSS DR2 radio continuum images of the same regions.
• Figure 4: Colour–mass diagram, where green-valley galaxies lie between the two green lines. The yellow star marks the FRB 20190303B host-galaxy candidate MCG+11-11-014. Contours indicate the SDSS spectroscopic sample 2015ApJS..219....8Chang. Green lines show the green valley defined by 2014MNRAS.440..889Schawinski.
• Figure 5: Radial surface brightness profiles of the candidate FRB 20190303B host galaxy MCG+11-11-014 in the $g$-band (left), $r$-band (middle), and the corresponding colour profile ($\mu_g - \mu_r$, right). Error bars represent photometric uncertainties propagated from the intensity measurements. The vertical dashed lines indicate the semi-major axis (SMA) radius corresponding to the FRB centre position. The colour profile shows a mild radial gradient, potentially reflecting variations in stellar population or internal dust attenuation.