The Effects of Metallicity and AGN Activity on the Mid-Infrared Dust Emission of Galaxies

TL;DR

This study investigates how metallicity and active galactic nuclei (AGN) activity influence mid-infrared dust emission in galaxies, revealing correlations with specific dust emission ratios and discussing potential underlying physical mechanisms.

Contribution

It provides new empirical evidence linking metallicity and AGN activity to MIR dust emission ratios, suggesting dust formation/destruction processes and AGN effects as underlying causes.

Findings

Metallicity correlates with PAH-to-star, VSG-to-star, and PAH-to-VSG ratios.

AGN activity influences MIR dust emission ratios, possibly through PAH destruction or VSG continuum enhancement.

Correlations can be explained by dust formation/destruction processes and AGN-related effects.

Abstract

Using a sample of the $Spitzer$ SWIRE-field galaxies whose optical spectra are taken from the Data Release 4 of the Sloan Digital Sky Survey, we study possible correlations between the Mid-InfraRed (MIR) dust emission from these galaxies and both their metallicities and AGN activities. We find that both metallicity and AGN activity are well correlated with the following ratios: PAH(Polycyclic Aromatic Hydrocarbon)-to-star, VSG(Very Small Grain)-to-star and PAH-to-VSG, which can be characterized by $\nu L_{\nu}[8\mu m({\rm dust})]/\nu L_{\nu}[3.6\mu m]$, $\nu L_{\nu}[24\mu m]/\nu L_{\nu}[3.6\mu m]$, and$\nu L_{\nu}[8\mu m({\rm dust})]/\nu L_{\nu}[24\mu m]$ respectively. We argue that our MIR-metallicity correlation could be explained by either the amount of dust (ongoing dust formation) or dust destruction (PAHs and VSGs could be destroyed by hard and intense radiation fields), and that the MIR-AGN correlation could arise due to either PAH destruction or an enhanced VSG continuum by the central AGN.