Spiral Galaxies

TL;DR

This paper discusses the classification and evolution of spiral galaxies, emphasizing the importance of galaxy surveys, the Hubble sequence, and the transition between different galaxy types based on star formation activity.

Contribution

It provides an overview of galaxy classification schemes and highlights key questions about galaxy evolution and transitions between categories.

Findings

Galaxy surveys have expanded our statistical understanding of galaxies.

The Hubble sequence remains a fundamental classification tool.

Understanding galaxy transitions is a major open question.

Abstract

Our vision of galaxies has changed significantly since the era of large galaxy surveys like the Sloan, which gave us extensive statistics with millions of galaxies. The Hubble sequence classification described in Chapter 1 still remains very widely used but has been enriched with broad categories based on color that indicate the recent formation of stars: the red sequence of passive galaxies, consisting solely of old stars, and the blue cloud of galaxies with active star formation. Chapter 3 focused on galaxies with a dominant spheroid, which are generally found on the red sequence. One of the key questions about the evolution of galaxies that remain to be answered is to understand how a galaxy can suddenly pass from one category to another. This is a graduate-student level lecture, not a review article.