# Mid-infrared extinction and fresh silicate dust towards the Galactic Center

## TL;DR

This study models the mid-infrared extinction towards the Galactic Center, proposing a dust composition of aromatic carbon and layered silicate particles with magnetite, to explain the flat extinction feature observed.

## Contribution

It introduces a new dust model using laboratory-measured optical constants and layered particles, improving the understanding of Galactic Center extinction.

## Key findings

- A mixture of aromatic carbon and layered silicate particles fits the extinction data.
- Metallic iron is likely embedded within dust particles, not layered on silicates.
- The dust is likely recently formed in late-type star atmospheres within the Galactic Center.

## Abstract

We interpret the interstellar extinction observed towards the Galactic Center (GC) in the wavelength range $\lambda = 1 - 20\,\mkm$. Its main feature is the flat extinction at $3 - 8\,\mkm$ whose explanation is still a problem for the cosmic dust models. We search for structure and chemical composition of dust grains that could explain the observed extinction. In contrast to earlier works we use laboratory measured optical constants and consider particles of different structure. We show that a mixture of compact grains of aromatic carbon and of some silicate is better suited for reproducing the flat extinction in comparison with essentially porous grains or aliphatic carbon particles. Metallic iron should be located inside the particle, i.e. cannot form layers on silicate grains as the extinction curves become then very peculiar. We find a model including aromatic carbonaceous particles and three-layered particles with an olivine-type silicate core, a thin very porous layer and a thin envelope of magnetite that provides a good (but still not perfect) fit to the observational data. We suggest that such silicate dust should be fresh, i.e. recently formed in the atmospheres of late-type stars in the central region of the Galaxy. We assume that this region has a radius of about 1 kpc and produces about a half of the observed extinction. The remaining part of extinction is caused by a "foreground" material being practically transparent at $\lambda = 4 - 8\,\mkm$.