An Observational Guide to Identifying Pseudobulges and Classical Bulges in Disk Galaxies

TL;DR

This paper reviews the observed properties of pseudobulges and classical bulges in disk galaxies, highlighting bimodal characteristics and proposing practical criteria for their identification based on empirical data.

Contribution

It provides a comprehensive summary of observable differences between bulge types and introduces new absorption line indices for distinguishing them.

Findings

Bimodality in morphology, structure, and kinematics of bulges

Identification of absorption line indices for bulge classification

Practical criteria for distinguishing pseudobulges from classical bulges

Abstract

In this review our aim is to summarize the observed properties of pseudobulges and classical bulges. We utilize an empirical approach to studying the properties of bulges in disk galaxies, and restrict our analysis to statistical proper- ties. A clear bimodality is observed in a number of properties including morphology, structural properties, star formation, gas content & stellar population, and kinematics. As well as summarizing known methods to identify pseudobulges and classical bulges we also show new results, including absorption line indices that can be used to identify different bulge types. We conclude by summarizing those properties that isolate pseudobulges from classical bulges. Our intention is to describe a practical, easy to use, list of criteria for identifying bulge types.