Dust/ice mixing in cold regions and solid-state water in the diffuse interstellar medium

TL;DR

This study compares laboratory silicate-water-ice spectra with astronomical data to show that water ice is likely mixed with dust in various cosmic environments, impacting our understanding of interstellar medium composition.

Contribution

It provides evidence that solid-state water is present in the diffuse interstellar medium through spectral comparison, advancing knowledge of dust-ice mixing in space.

Findings

Water ice is mixed with silicate grains in the interstellar medium.

Laboratory spectra can explain astronomical IR observations.

Solid-state water presence affects models of cosmic dust environments.

Abstract

Whether ice in cold cosmic environments is physically separated from the silicate dust or mixed with individual silicate moieties is not known. However, different grain models give very different compositions and temperatures of grains. The aim of the present study is a comparison of the mid-IR spectra of laboratory silicate-grains/water-ice mixtures with astronomical observations to evaluate the presence of dust/ice mixtures in interstellar and circumstellar environments. The laboratory data can explain the observations assuming reasonable mass-averaged temperatures for the protostellar envelopes and protoplanetary disks demonstrating that a substantial fraction of water ice may be mixed with silicate grains. Based on the combination of laboratory data and infrared observations, we provide evidence of the presence of solid-state water in the diffuse interstellar medium. Our results have implications for future laboratory studies trying to investigate cosmic dust grain analogues and for future observations trying to identify the structure, composition, and temperature of grains in different astrophysical environments.