Leslie E. Kuchinski

Attenuation Effects in Spiral Galaxies: Multiwavelength Photometry and Disk Radiative Transfer Models

?????We present a quantitative investigation of the optical depth through spiral disks using BVRIJHK colors of 15 highly inclined Sab?Sc spirals and new models for radiative transfer in stellar disks. The models include exponential stellar and dust disks, exponential stellar bulge components, multiple scattering, and both homogeneous and clumpy dust distributions. Preliminary comparisons of the observed optical and near-infrared (NIR) color gradients across galaxy dust lanes with predictions from radiative transfer models with slab and spherical shapes underscore the need for these realistic exponential disk geometries. When compared with the extent of reddening predicted by the disk models, the maximum optical and NIR color excesses in galaxy dust lanes imply central face-on optical depths of 0.5?2.0 in the V band. For these highly inclined systems, we find this inferred optical depth to be largely insensitive to the difference between clumpy and homogeneous dust distributions. Comparisons of galaxy color gradients to models with high central optical depths contradict the often-stated claim that spiral disks are opaque out to D25. Our derived optical depths show that the predicted radial color changes caused by attenuation in face-on galaxies are much smaller than the observed color gradients in such systems, which suggests that the observed changes are the result of variations in stellar content. The face-on optical depths also imply that, when viewed edge-on, galaxy dust lanes have optical depths greater than 1.0 even in the K band and, thus, the NIR mass-to-light ratio changes across dust features.

Discovery of a Boxy Peanut-shaped Bulge in the Near-Infrared

We report on the discovery of a boxy peanut-shaped bulge in the highly inclined barred Seyfert 2 galaxy NGC 7582. The peanut shape is clearly evident in near-infrared JHK images but is obscured by extinction from dust in visible BVR images. These facts suggest that near-infrared imaging surveys will discover a larger number of boxy peanut morphologies than visible surveys, particularly in galaxies with heavy extinction, such as NGC 7582. The bulge in NGC 7582 exhibits strong boxiness compared to other boxy peanut shaped bulges. If the starburst was mediated by the bar, then it is likely that the bar formed in less than a few bar rotation periods, i.e., a few ×108 yr ago. If the bar also caused the peanut, then the peanut formed quickly, on a timescale of a few bar rotation periods.

Infrared Photometry and Dust Absorption in Highly Inclined Spiral Galaxies

We have begun an extensive study of the structure and kinematics of bulges, especially those with boxy or peanut shaped morphology. In particular, we wish to investigate the possible connection between boxy bulges and bars (e.g., Kuijken & Merrifield 1995)