Near-Infrared Structure of Fast and Slow Rotating Disk Galaxies

TL;DR

This study examines the structure of stellar disks in six nearby edge-on spiral galaxies using high-resolution infrared imaging and 3D models, revealing diverse disk features related to galaxy rotation speed and environment.

Contribution

It provides new insights into the diversity of disk structures in spiral galaxies, especially comparing fast and slow rotators, and highlights the role of super-thin disks and truncations.

Findings

Fast rotators often have complex, nested disk structures.

Super-thin disks contribute significantly to infrared light and are linked to star formation.

Inner disk truncations are common in fast-rotating galaxies.

Abstract

We investigate the stellar disk structure of six nearby edge-on spiral galaxies using high-resolution JHKs-band images and 3D radiative transfer models. To explore how mass and environment shape spiral disks, we selected galaxies with rotational velocities between 69 < Vrot < 245 km/sec, and two with unusual morphologies. We find a wide diversity of disk structure. Of the fast-rotating (Vrot > 150 km/sec) galaxies, only NGC 4013 has the super-thin+thin+thick nested disk structure seen in NGC 891 and the Milky Way, albeit with decreased oblateness, while NGC 1055, a disturbed massive spiral galaxy, contains disks with hz $\lesssim$ 200 pc. NGC 4565, another fast-rotator, contains a prominent ring at a radius ~5 kpc but no super-thin disk. Despite these differences, all fast-rotating galaxies in our sample have inner truncations in at least one of their disks. These truncations lead to Freeman Type II profiles when projected face-on. Slow-rotating galaxies are less complex, lacking inner disk truncations and requiring fewer disk components to reproduce their light distributions. Super-thin disk components in undisturbed disks contribute ~25% of the total Ks-band light, up to that of the thin-disk contribution. The presence of super-thin disks correlates with infrared flux ratios; galaxies with super-thin disks have f(Ks)/f(60 $\mu$m) $\leq$ 0.12 for integrated light, consistent with super-thin disks being regions of on-going star-formation. Attenuation-corrected vertical color gradients in (J-Ks) correlate with the observed disk structure and are consistent with population gradients with young-to-intermediate ages closer to the midplane, indicating that disk heating-or cooling-is a ubiquitous phenomenon.