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

TL;DR

This paper reviews the nature of galactic bulges, distinguishing classical bulges from pseudo-bulges, based on integral field spectroscopy data revealing their kinematic and stellar population properties.

Contribution

It provides a comprehensive analysis of bulge types using 2D spectroscopic data, clarifying their structural and dynamical differences in early-type spiral galaxies.

Findings

Pseudo-bulges show disk-like kinematics and stellar populations.

Classical bulges resemble elliptical galaxies in structure and dynamics.

Bulge classification aids understanding galaxy formation and evolution.

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.