The host of GRB 171205A in 3D -- A resolved multiwavelength study of a rare grand-design spiral GRB host

TL;DR

This study provides a detailed 3D multiwavelength analysis of the GRB 171205A host galaxy, revealing its spiral structure, metallicity gradient, and star formation regions, and shows GRBs can occur in diverse star-forming environments.

Contribution

It presents the most detailed spatially resolved study of a GRB host galaxy, combining multiple data sources to analyze its structure, metallicity, and star formation in unprecedented detail.

Findings

GRB site has low metallicity and high star formation

Star formation is concentrated in specific regions, including the GRB site

Gas inflow or interactions may trigger star formation without clear ionized/molecular gas signatures

Abstract

Long GRB hosts at z<1 are usually low-mass, low metallicity star-forming galaxies. Here we present the until now most detailed, spatially resolved study of the host of GRB 171205A, a grand-design barred spiral galaxy at z=0.036. Our analysis includes MUSE integral field spectroscopy, complemented by high spatial resolution UV/VIS HST imaging and CO(1-0) and HI 21cm data. The GRB is located in a small star-forming region in a spiral arm of the galaxy at a deprojected distance of ~ 8 kpc from the center. The galaxy shows a smooth negative metallicity gradient and the metallicity at the GRB site is half solar, slightly below the mean metallicity at the corresponding distance from the center. Star formation in this galaxy is concentrated in a few HII regions between 5-7 kpc from the center and at the end of the bar, inwards of the GRB region, however, the HII region hosting the GRB is in the top 10% of regions with highest specific star-formation rate. The stellar population at the GRB site has a very young component (< 5 Myr) contributing a significant part of the light. Ionized and molecular gas show only minor deviations at the end of the bar. A parallel study found an asymmetric HI distribution and some additional gas near the position of the GRB, which might explain the star-forming region of the GRB site. Our study shows that long GRBs can occur in many types of star-forming galaxies, however, the actual GRB sites consistently have low metallicity, high star formation and a young population. Furthermore, gas inflow or interactions triggering the star formation producing the GRB progenitor might not be evident in ionized or even molecular gas but only in HI.