Toward understanding the 3.4 micron and 9.7 micron extinction feature variations from the local diffuse interstellar medium to the Galactic center

TL;DR

This study investigates the variations in specific infrared extinction features from the local diffuse interstellar medium to the Galactic center, using a porous dust model to explain observed differences in dust composition and optical properties.

Contribution

It introduces a porous dust model incorporating amorphous silicate, carbonaceous organic refractory dust, and water ice to explain extinction feature variations across different galactic environments.

Findings

The model reproduces the observed ratios of A_V to au_sil and au_ahc.

Porous dust structure explains the variation in extinction features.

Water ice presence is significant in Galactic center dust.

Abstract

Observationally, both the 3.4micron aliphatic hydrocarbon C--H stretching absorption feature and the 9.7micron amorphous silicate Si--O stretching absorption feature show considerable variations from the local diffuse interstellar medium (ISM) to Galactic center (GC): both the ratio of the visual extinction (A_V) to the 9.7micron Si--O optical depth (\tausil) and the ratio of A_V to the 3.4micron C--H optical depth (\tauahc) of the solar neighborhood local diffuse ISM are about twice as much as that of the GC. In this work, we try to explain these variations in terms of a porous dust model consisting of a mixture of amorphous silicate, carbonaceous organic refractory dust (as well as water ice for the GC dust).