Modelling extragalactic extinction through gamma-ray burst afterglows

TL;DR

This study models extragalactic dust extinction using a dynamic dust grain model based on gamma-ray burst afterglows, revealing evolutionary trends in dust composition related to galactic activity and redshift.

Contribution

It introduces a time-dependent dust model with core-mantle particles and PAHs, fitting observed extinction profiles and linking dust evolution to galaxy activity and cosmic time.

Findings

Carbon structure becomes more aliphatic with galactic activity

Molecular component's role increases in younger objects

Model successfully fits most observed extinction profiles

Abstract

We analyze extragalactic extinction profiles derived through gamma-ray burst afterglows, using a dust model specifically constructed on the assumption that dust grains are not immutable but respond time-dependently to the local physics. Such a model includes core-mantle spherical particles of mixed chemical composition (silicate core, sp2 and sp3 carbonaceous layers), and an additional molecular component, in the form of free-flying polycyclic aromatic hydrocarbons. We fit most of the observed extinction profiles. Failures occur for lines of sight presenting remarkable rises blueward the bump. We find a tendency in the carbon chemical structure to become more aliphatic with the galactic activity, and to some extent with increasing redshifts. Moreover, the contribution of the moleclar component to the total extinction is more important in younger objects. The results of the fitting procedure (either successes and failures) may be naturally interpreted through an evolutionary prescription based on the carbon cycle in the interstellar medium of galaxies.