Host Galaxy Properties of Gamma-ray Bursts Involving Neutron Star Binary Mergers and Its Impact on Kilonovae Rates

TL;DR

This study analyzes the properties of host galaxies of short and hybrid gamma-ray bursts to better understand neutron star mergers and improve strategies for gravitational wave follow-up observations.

Contribution

It introduces a new formulation for the BNS merger rate based on host galaxy properties, challenging previous assumptions about mass proportionality.

Findings

Host galaxies of sGRBs are less massive than the control sample.

A new model relates BNS merger rate to galaxy mass and sSFR.

Insights aid targeted GW follow-ups and host galaxy identification.

Abstract

In the upcoming gravitational wave (GW) observing runs, identifying host galaxies is crucial as it provides essential redshift information and enables the use of GW events as standard sirens. However, pinpointing host galaxies remains challenging due to the large localization uncertainties and the rapidly fading nature of their optical counterparts. Analyzing the host galaxies of short gamma-ray bursts (sGRBs) offers an alternative approach to deepen our understanding of the environments where binary neutron stars (BNS) primarily merge. This study compiles archival photometric data for the host galaxies of 76 sGRBs and 4 hybrid GRBs that are long GRBs accompanied by kilonova-like signals. We use this data to evaluate their physical properties through spectral energy distribution (SED) fitting. To assess the characteristics of the host galaxies, we utilized a volume-limited sample ($z<0.5$) from the COSMOS field as a control group. Contrary to expectations that the BNS merger rate is proportional to host stellar mass, the short and hybrid GRB population appears less massive than the mass-weighted distribution of the control sample. Instead, we propose a formulation for the expected BNS merger rate from a galaxy as $\log(n_{\mathrm{BNS}}/\mathrm{Gyr}) = 0.86 \times \log(M_*/M_{\odot}) + 0.44 \times \log(\mathrm{sSFR}/\mathrm{yr}) + 0.857$, which optimally explains the deviation between the stellar mass distributions of the GRB host galaxies and the control sample. These insights provide a strategic framework for targeted GW follow-ups and enhance our ability to identify potential host galaxies for future GW events.