Infall and accretion

TL;DR

This paper reviews the role of gas infall and accretion in galaxy formation, highlighting processes like cold accretion, feedback cycles, and environmental effects on star formation and galaxy evolution.

Contribution

It provides a comprehensive review of accretion processes, including cold accretion, feedback mechanisms, and their impact on galaxy evolution and star formation.

Findings

Cold accretion may solve the angular momentum problem.

Gas accretion drives secular evolution and star formation.

Feedback processes regulate cooling flows and galaxy activity.

Abstract

Gas infall and accretion play a fundamental role in galaxy formation, and several processes of accretion are reviewed. In particular the cold accretion may solve to some extent the angular momentum problem in disk formation, while it is aggravated by mergers. Gas accretion is one of the main actor in secular evolution: it is required to account for recurrent bar formation, and to explain the feedback cycles of formation of bulges and black holes, with correlated masses. Infall is also required to fuel a regular and almost stationary star formation history. Star formation is quenched for galaxy in clusters when gas accretion is suppressed through stripping. The central brighter central galaxy can benefit however of gas accretion through cooling flows, moderated by AGN feedback. Hot and cold feedback scenarios can be considered, to account for a stationary cooling flow, and explain the filamentary CO and Halpha observed structures.