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27th of February 2024
A MeerKAT image of the host galaxy of the Fast Radio Burst FRB20230718A, with the ASKAP localisation marked.
HI, FRB, What’s Your z?
by Glowacki et al.
Identification and follow-up observations of the host galaxies of fast radio bursts (FRBs) not only help us understand the environments in which the FRB progenitors reside, but also provide a unique way of probing the cosmological parameters using the dispersion measures (DMs) of FRBs and distances to their origin. A fundamental requirement is an accurate distance measurement to the FRB host galaxy, but for some sources viewed through the Galactic plane, optical/near-infrared spectroscopic redshifts are extremely difficult to obtain due to dust extinction.

FRB 20230718A is an apparently non-repeating FRB detected in the Commensal Real-time ASKAP Fast Transients survey and localized 0.4 degrees from the Galactic plane, making optical follow-up challenging. Glowacki et al. have reported the first radio-based spectroscopic redshift measurement for an FRB host galaxy, through detection of its neutral hydrogen (HI) 21 cm emission using MeerKAT observations, obtaining a redshift of z = 0.0357. The MeerKAT observations also reveal that the FRB host galaxy is interacting with a nearby companion, which is evident from the detection of an H I bridge connecting the two galaxies. A subsequent optical spectroscopic observation confirmed an FRB host galaxy redshift of 0.0359. This result demonstrates the value of HI to obtain redshifts of FRBs at low Galactic latitudes and redshifts. Such nearby FRBs, which have Dispersion Measures (DMs) dominated by the Milky Way, can be used to characterize these components and thus better calibrate the remaining cosmological contribution to dispersion for more distant FRBs. This provides a strong lever arm to examine the Macquart relation between cosmological DM and redshift. The image above is the MeerKAT HI intensity map, with radio contours overlaid on a DECam three-color image. The ASKAP FRB localization region is given by the cyan ellipse, enlarged by a factor of 5 for visibility, and is coincident with a peak in H I emission and a faint, apparently red, optical galaxy.

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