Shock fronts in the long GRB031203 host galaxy

TL;DR

This study models the spectra of the long GRB031203 host galaxy over several years, revealing shock-driven emission processes, evolving physical conditions, and sub-solar metallicities in the galaxy's gas.

Contribution

It provides a detailed shock and photoionization model of the galaxy's emission lines, showing temporal changes in shock velocities and metallicities, which is novel in GRB host galaxy analysis.

Findings

Shock velocities and ionization parameters decrease over time.

Gas metallicities are significantly below solar levels.

Broad line components indicate stellar wind shocks.

Abstract

The detailed modelling of the spectra observed from the long GRB031203 host galaxy at different epochs during the 2003-2009 years is presented. The line profiles show FWHM of about 100 km/s. A broad line profile with FWHM < 400 km/s appears in the line sockets from the 2009 observations. We suggest that the narrow lines show the velocity of star-burst (SB) debris, while the broad ones are due to the wind from SB stars. The spectra are emitted from the gas downstream of different shock fronts which are at work on the edges of the emitting clouds. A head-on-back shock appears when the wind from the SB stars reaches the internal edge of the SB debris moving outwards. A head-on shock is created by collision of the debris with the ISM clouds.Line ratios in both cases are calculated by the coupled effect of shock and photoionization from the SB. The models selected by fitting the calculated to the observed line ratios show that the ionization parameters, the shock velocities and the gas pre-shock densities slowly decrease with time.Oxygen metallicities (12+log(O/H)=8.3-8.48) are lower than solar (8.82) by a factor <3 and nitrogen metallicities are lower than solar (12+log(N/H)=8.0) by factors of 3-5.