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arXiv · 1903.00485

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

M. Arabsalmani·S. Roychowdhury·T. K. Starkenburg·L. Christensen·E. Le Floc'h·N. Kanekar·F. Bournaud·M. A. Zwaan·J. P. U. Fynbo·P. Møller·E. Pian
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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 $\rm0.004\,M_{\odot}\, yr^{-1}$, a gas mass of $10^{7.1\pm0.1} M_{\odot}$, and a stellar mass of $10^{7.0\pm0.3} M_{\odot}$. The interaction between ESO 184$-$G82 and GALJ193510-524947 is evident from the extended gaseous structure between the two galaxies in the GMRT HI 21 cm map. We find a ring of high column density HI 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.

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M. Arabsalmani, S. Roychowdhury, T. K. Starkenburg, L. Christensen, E. Le Floc'h, N. Kanekar, F. Bournaud, M. A. Zwaan, J. P. U. Fynbo, P. Møller, E. Pian. 2019-03-01. The host galaxy of GRB 980425 / SN1998bw: a collisional ring galaxy. https://doi.org/10.1093/mnras%2Fstz735

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