Variations in 24 micron morphologies among galaxies in the Spitzer Infrared Nearby Galaxies Survey: New insights into the Hubble sequence

TL;DR

This study analyzes 24 micron and 3.6 micron morphologies of 73 nearby galaxies, revealing how dust emission distribution varies with galaxy type and differs from stellar emission, providing new insights into galaxy structure and star formation.

Contribution

It introduces a detailed morphological analysis of dust emission at 24 microns across the Hubble sequence, highlighting differences from stellar emission and the influence of galaxy features.

Findings

Early-type galaxies are compact and centralized in 24 micron emission.

Late-type galaxies tend to be extended and asymmetric in 24 micron emission.

Variations in dust morphology correlate with galaxy type and star formation activity.

Abstract

To study the distribution of star formation and dust emission within nearby galaxies, we measured five morphological parameters in the 3.6 and 24 micron wave bands for 65 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS) and 8 galaxies that were serendipitously observed by SINGS. The morphological parameters demonstrate strong variations along the Hubble sequence, including statistically significant differences between S0/a-Sab and Sc-Sd galaxies. Early-type galaxies are generally found to be compact, centralized, symmetric sources in the 24 micron band, while late-type galaxies are generally found to be extended, asymmetric sources. These results suggest that the processes that increase the real or apparent sizes of galaxies' bulges also lead to more centralized 24 micron dust emission. Several phenomena, such as strong nuclear star formation, Seyfert activity, or outer ring structures, may cause galaxies to deviate from the general morphological trends observed at 24 microns. We also note that the 24 micron morphologies of Sdm-Im galaxies are quite varied, with some objects appearing very compact and symmetric while others appear diffuse and asymmetric. These variations reflect the wide variation in star formation in irregular galaxies as observed at other wavelengths. The variations in the 24 micron morphological parameters across the Hubble sequence mirror many of the morphological trends seen in other tracers of the ISM and in stellar emission. However, the 24 micron morphological parameters for the galaxies in this sample do not match the morphological parameters measured in the stellar wave bands. This implies that the distribution of dust emission is related to but not equivalent to the distribution of stellar emission.