On classical and pseudobulges: The nature of bulges of early-type spirals

Abstract

Historically, galactic bulges are thought to be elliptical galaxy-like objects sitting in the middle of a generally larger disk. There are, however, more and more claims that some bulges are much more similar to disks. John Kormendy has named these bulges pseudo-bulges. In this paper I discuss some recent integral field spectroscopy of the SAURON collaboration on a sample of 24 Sa and Sab galaxies. Using their 2-dimensional maps of the stellar velocity, velocity dispersion, and absorption line strength, it is now much easier to understand the nature of nearby galactic bulges. I review several aspects of bulges, namely the surface photometry, stellar kinematics, stellar populations, presence of interstellar matter, and their behavior in the fundamental plane of early-type galaxies.