Comparison of dust-to-gas ratios in luminous, ultraluminous, and hyperluminous infrared galaxies

TL;DR

This study models the spectral energy distributions of luminous infrared galaxies to compare their dust-to-gas ratios, revealing differences across galaxy luminosity classes and the frequent presence of AGNs.

Contribution

It provides a detailed analysis of dust-to-gas ratios in various IR galaxy classes using spectral modeling, highlighting the role of different cloud types and AGN prevalence.

Findings

Dust-to-gas ratios are about 0.1 in luminous and ultraluminous IR galaxies.

Hyperluminous IR galaxies generally have lower dust-to-gas ratios.

Most ultraluminous IR galaxies host AGNs.

Abstract

The dust-to-gas ratios in three different samples of luminous, ultraluminous, and hyperluminous infrared galaxies are calculated by modelling their radio to soft X-ray spectral energy distributions using composite models which account for the photoionizing radiation from HII regions, starbursts, or AGNs, and for shocks. The models are limited to a set which broadly reproduces the mid-IR fine structure line ratios of local, IR bright, starburst galaxies. The results show that two types of clouds contribute to the IR emission. Those characterized by low shock velocities and low preshock densities explain the far-IR dust emission, while those with higher velocities and densities contribute to mid-IR dust emission. An AGN is found in nearly all of the ultraluminous IR galaxies and in half of the luminous IR galaxies of the sample. High IR luminosities depend on dust-to-gas ratios of about 0.1 by mass, however, most hyperluminous IR galaxies show dust-to-gas ratios much lower than those calculated for the luminous and ultraluminous IR galaxies.