# Low temperature MIR to submillimeter mass absorption coefficient of interstellar dust analogues I: Mg-rich glassy silicates

## TL;DR

This study measures the mass absorption coefficient of Mg-rich glassy silicate dust analogues at low temperatures, revealing complex behaviors that impact astrophysical dust modeling and interpretation of cold dust emission.

## Contribution

It provides new spectroscopic data on realistic interstellar dust analogues, showing temperature-dependent MAC variations and highlighting discrepancies with existing cosmic dust models.

## Key findings

- MAC increases with temperature above 30K due to thermally activated processes
- MAC behavior is complex and cannot be described by a single power law
- Analogues are more emissive than current cosmic dust models, affecting mass estimates

## Abstract

A wealth of data from the Herschel and Planck satellites and now from ALMA, revealing cold dust thermal emission, is available for astronomical environments ranging from interstellar clouds, cold clumps, circumstellar envelops, and protoplanetary disks. The interpretation of these observations relies on the understanding and modeling of cold dust emission and on the knowledge of the dust optical properties. The aim of this work is to provide astronomers with a set of spectroscopic data of realistic interstellar dust analogues that can be used to interpret the observations. Glassy silicates of mean composition (1-x)MgO - xSiO2 with x = 0.35, 0.40 and 0.50 were synthesized. The mass absorption coefficient (MAC) of the samples was measured in the spectral domain 30 - 1000 $\mu$m for grain temperature in the range 300 K - 10 K and at room temperature in the 5 - 40 $\mu$m domain. We find that the MAC of all samples varies with the grains temperature. In the FIR/submm, and above 30K, the MAC value at a given wavelength increases with the temperature as thermally activated absorption processes appear. The studied materials exhibit different and complex behaviors at long wavelengths (lambda $\geq$ 200 to 700 $\mu$m depending on the samples) and the MAC cannot be approximated by a single power law in ${\lambda}^{-\beta}$. These behaviors are attributed to the amorphous nature of dust and to the amount and nature of the defects within this amorphous structure. Above 20 $\mu$m, the measured MAC are much higher than the MAC calculated from interstellar silicate dust models indicating that the analogues measured in this study are more emissive than the silicates in cosmic dust models. This has important astrophysical implications because masses are overestimated by the models. Moreover, constraints on elemental abundance of heavy elements in cosmic dust models are relaxed