First IFU observations of two GRB host galaxies at cosmic noon with JWST/NIRSpec

Abstract

Long gamma-ray bursts (GRBs) serve as powerful probes of distant galaxies. Their luminous afterglow pinpoints galaxies independent of luminosity, in contrast to most flux-limited surveys. Nevertheless, GRB-selected galaxy samples are not free from bias, instead tracing the conditions favoured by the progenitor stars. Characterizing the galaxy populations traced by GRBs is therefore important both to effectively use GRBs as probes as well as to place stronger constraints on the progenitor stars capable of forming long GRBs. Spatially resolved spectroscopic observations with integral field units (IFUs) provide valuable insights into the interstellar medium and stellar populations of GRB host galaxies. In this paper, we present results of the first two GRB host galaxies observed with the JWST/Near-Infrared Spectrograph IFU with a spatial resolution of ∼ 1.6 kpc; the hosts of GRB 150403A and GRB 050820A at redshifts z ∼ 2.06 and ∼ 2.61, respectively. The data reveal two complex galaxy environments made up of two or more star-forming galaxies that are likely interacting given their small spatial separation (< 20 kpc) and line-of-sight velocity offsets (< 100 kms-1). The measured gas-phase metallicity, star formation rates (SFRs), and key diagnostic line ratios for each of the detected galaxies are o v erall consistent with the properties of other star-forming galaxies and GRB hosts at z > 2. Ho we ver, dif ferences in the SFR and metallicities of the interacting galaxies highlight the importance of spatially resolved observations in order to accurately characterize the galaxy properties traced by GRBs.