The feeding of activity in galaxies: a molecular line perspective

TL;DR

This paper reviews the NUGA survey's high-resolution molecular gas observations in galaxy centers, revealing diverse fueling mechanisms for low-luminosity AGNs and emphasizing the role of secular evolution and dynamical decoupling.

Contribution

It provides new insights into the gas dynamics and fueling processes of AGNs through detailed molecular line observations and gravity torque analysis.

Findings

Only about one-third of surveyed galaxies show active fueling.

Diverse gas instabilities are observed in galaxy centers.

Secular evolution influences AGN fueling cycles.

Abstract

What are the main drivers of activity in the local universe? Observations have been instrumental in identifying the mechanisms responsible for fueling activity in galaxy nuclei. In this context we summarize the main results of the NUclei of GAlaxies (NUGA) survey. The aim of NUGA is to map, at high resolution and high sensitivity, the distribution and dynamics of the molecular gas in the central kiloparsec region of 25 galaxies, and to study the different mechanisms responsible for gas fueling of low-luminosity AGNs (LLAGN). Gas flows in NUGA maps reveal a wide range of instabilities. The derived gravity torque maps show that only about 1/3 of NUGA galaxies show evidence of ongoing fueling. Secular evolution and dynamical decoupling are seen to be key ingredients to understand the AGN fueling cycle. We discuss the future prospects for this research field with the advent of instruments like the Atacama Large Millimeter Array (ALMA).