Exploring the millimetre emission in nearby galaxies: analysis of the edge-on galaxy NGC 891

TL;DR

This study presents new millimetre observations of the edge-on galaxy NGC 891, analyzing its physical properties and emission components across multiple wavelengths to understand its dust, gas, and radio emission characteristics.

Contribution

It provides detailed multiwavelength SED fitting of NGC 891 using HerBIE, revealing the galaxy's morphology and emission contributions at millimetre wavelengths.

Findings

Millimetre morphology similar to cold dust and molecular gas.

Radio emission negligible at 1.15 mm, ~10% at 2 mm, dominant beyond 5 mm.

Free-free emission distribution resembles dust thermal emission.

Abstract

New observations of the edge-on galaxy NGC 891, at 1.15 and 2 mm obtained with the IRAM 30-m telescope and the NIKA2 camera, within the framework of the IMEGIN (Interpreting the Millimetre Emission of Galaxies with IRAM and NIKA2) Large Program, are presented in this work. By using multiwavelength maps (from the mid-IR to the cm wavelengths) we perform SED fitting in order to extract the physical properties of the galaxy on both global and local ($\sim$kpc) scales. For the interpretation of the observations we make use of a state-of-the-art SED fitting code, HerBIE (HiERarchical Bayesian Inference for dust Emission). The observations indicate a galaxy morphology, at mm wavelengths, similar to that of the cold dust emission traced by sub-mm observations and to that of the molecular gas. The contribution of the radio emission at the NIKA2 bands is very small (negligible at 1.15 mm and $\sim10\%$ at 2 mm) while it dominates the total energy budget at longer wavelengths (beyond 5 mm). On local scales, the distribution of the free-free emission resembles that of the dust thermal emission while the distribution of the synchrotron emission shows a deficiency along the major axis of the disc of the galaxy.