The host galaxy of GRB 980425/SN1998bw: a collisional ring galaxy

E Le Floc’H,E Pian,F Bournaud,J P U Fynbo,L Christensen,M A Zwaan,M Arabsalmani,N Kanekar,P Møller,S Roychowdhury,T K Starkenburg

doi:10.1093/mnras/stz735

Abstract

ABSTRACT We report Giant Metrewave Radio Telescope (GMRT), Very Large Telescope (VLT), and Spitzer Space Telescope observations of ESO 184−G82, the host galaxy of GRB 980425/SN 1998bw, that yield evidence of a companion dwarf galaxy at a projected distance of 13 kpc. The companion, hereafter GALJ193510-524947, is a gas-rich, star-forming galaxy with a star formation rate of $\rm 0.004\, M_{\odot }\, yr^{-1}$, a gas mass of $10^{7.1\pm 0.1} \, \mathrm{M}_{\odot}$, and a stellar mass of $10^{7.0\pm 0.3} \, \mathrm{M}_{\odot}$. The interaction between ESO 184−G82 and GALJ193510-524947 is evident from the extended gaseous structure between the two galaxies in the GMRT H i 21 cm map. We find a ring of high column density H i gas, passing through the actively star-forming regions of ESO 184−G82 and the GRB location. This ring lends support to the picture in which ESO 184−G82 is interacting with GALJ193510-524947. The massive stars in GALJ193510-524947 have similar ages to those in star-forming regions in ESO 184−G82, also suggesting that the interaction may have triggered star formation in both galaxies. The gas and star formation properties of ESO 184−G82 favour a head-on collision with GALJ193510-524947 rather than a classical tidal interaction. We perform state-of-the-art simulations of dwarf–dwarf mergers and confirm that the observed properties of ESO 184−G82 can be reproduced by collision with a small companion galaxy. This is a very clear case of interaction in a gamma-ray burst host galaxy and of interaction-driven star formation giving rise to a gamma-ray burst in a dense environment.

Highlights

Long duration Gamma Ray Bursts (GRBs) are luminous explosions in the Universe, with powerful energy releases that make them detectable back to when the first stars and galaxies were formed (e.g., Tanvir et al 2009)
We report Giant Metrewave Radio Telescope (GMRT), Very Large Telescope (VLT) and Spitzer Space Telescope observations of ESO 184−G82, the host galaxy of GRB 980425/SN 1998bw, that yield evidence of a companion dwarf galaxy at a projected distance of 13 kpc
We derive a total HI mass of 108.90±0.04 M⊙ for the main gas disc from the total HI flux measured at this resolution, consistent with the value we reported in Arabsalmani et al (2015)

Summary

INTRODUCTION

Long duration Gamma Ray Bursts (GRBs) are luminous explosions in the Universe, with powerful energy releases that make them detectable back to when the first stars and galaxies were formed (e.g., Tanvir et al 2009). HI 21 cm mapping studies with radio interferometers allow the possibility of tracing the spatial distribution and velocity fields of the neutral hydrogen in nearby galaxies Such HI 21 cm studies of GRB host galaxies provide a powerful tool to directly test the hypothesis that an interaction might have triggered the star formation that gave rise to the GRB. In Arabsalmani et al (2015), we used the Giant Metrewave Radio Telescope (GMRT) to map the HI 21 cm emission from ESO 184−G82, finding its gas disc to be disturbed, while the global gas properties of the galaxy appeared similar to those of local dwarfs This was the first tentative evidence that interactions or a merger event might have played a role in the recent star formation activity of ESO 184−G82.

HI 21 cm emission observations

Ancillary data

Findings

DISCUSSION

SUMMARY