NEAR-INFRARED STRUCTURE OF FAST AND SLOW-ROTATING DISK 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.