The Bulge of M31

TL;DR

This paper reviews the complex stellar populations and kinematics of M31's bulge, highlighting unresolved questions about its formation history despite extensive recent data collection.

Contribution

It compiles and analyzes a decade of data on M31's bulge, emphasizing the need to understand its formation mechanisms.

Findings

Bulge kinematics differ from elliptical subgalaxies.

Extensive data on M31's stellar populations has been collected.

The formation history of M31's bulge remains an open question.

Abstract

Bulges are not just elliptical subgalaxies situated in the centers of large spirals. It might seem that way from their ages and chemistry, but bulge kinematics have been known to be different since the first long slit spectra were obtained. M31 presents the best opportunity to investigate all the issues of the stellar populations of bulges. This review collects the array of probing data that has been accumulated in the last decade. But the intriguing question `how did it form like this ?' remains.