Finding the one: identifying the host of compact binary mergers
by
Finding the host galaxies of stellar-mass compact binary mergers will open a new window for study-ing their formation histories and measuring key cosmological parameters, such as the Hubble constant. To date, only one merger, GW170817, has had its host galaxy confidently identified through electro-magnetic counterpart observations. The large localization volumes from the LIGO–Virgo–KAGRA (LVK) network, combined with the lack of electromagnetic emission for most events, make host iden-tification challenging. However, as the sensitivity of the gravitational-wave (GW) detector network improves, events are becoming increasingly well localized. Furthermore, galaxy luminosity traces mass or star formation rate, and thus correlates with the probability of hosting a merger. Focusing on the most luminous galaxies within the localization volumes of the best-localized GW events, we estimate the corresponding Hubble constant for each galaxy by combining its redshift with the luminosity dis-tance inferred from LVK observations. For the well-localized LVK events S250207bg, GW190814, and S250830bp, we find only 1, 1, and 4 galaxies, respectively, when restricting the analysis to the most luminous 1% of galaxies above Lth ∼ 1011h−2L⊙ in each event’s localization volume and adopting a broad H0 prior. The probability of these galaxies being random, and not associated with the GW events, is 29–36% across the three events. We encourage further follow-up observations of these candi-date host galaxies. We expect this approach to become increasingly powerful in future LVK observing runs, enabling constraints on merger formation histories and measurements of the Hubble constant.
arXiv link: https://arxiv.org/pdf/2604.28132