The metallicity properties of simulated long-GRB galaxy hosts and the Fundamental Metallicity Relation

TL;DR

This study combines simulations and models to explore how metallicity and star formation influence long-GRB host galaxies, finding star formation rate is the key factor rather than metallicity alone.

Contribution

It demonstrates that metallicity is not the primary parameter for LGRB hosts, emphasizing the role of star formation rate and explaining the scarcity of LGRBs in massive, dusty galaxies.

Findings

Low metallicity in observed hosts is due to high star formation environments.

Star formation rate is the main driver for LGRB occurrence.

Few LGRBs are observed in massive, dusty galaxies, aligning with dark LGRB fractions.

Abstract

We study the implication of the collapsar model for Long Gamma-Ray Bursts (LGRBs) on the metallicity properties of the host galaxies, by combining high-resolution N-body simulations with semi-analytic models of galaxy formation. The cosmological model that we use reproduces the Fundamental Metallicity Relation recently discovered for the SDSS galaxies, whereby the metallicity decreases with increasing Star Formation Rate for galaxies of a given stellar mass. We select host galaxies housing pockets of gas-particles, young and with different thresholds in metallicities, that can be sites of LRGB events, according to the collapsar model. The simulated samples are compared with 18 observed LGRB hosts in the aim at discriminating whether the metallicity is a primary parameter. We find that a threshold in metallicity for the LGRB progenitors, within the model galaxies, is not necessary in order to reproduce the observed distribution of host metallicities. The low metallicities of observed LGRB hosts is a consequence of the high star formation environment. The star formation rate appears to be the primary parameter to generate a burst event. Finally, we show that only a few LGRBs are observed in massive, highly extincted galaxies, while these galaxies are expected to produce many such events. We identify these missing events with the fraction of dark LGRBs.