The Co-Evolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe (1403.4620v1)

Abstract: We summarize what large surveys of the contemporary universe have taught us about the physics and phenomenology of the processes that link the formation and evolution of galaxies and their central supermassive black holes. We present a picture in which the population of AGN can be divided into two distinct populations. The Radiative-Mode AGN are associated with black holes that produce radiant energy powered by accretion at rates in excess of ~1% of the Eddington Limit. They are primarily associated with less massive black holes growing in high-density pseudo-bulges at a rate sufficient to produce the total mass budget in these black holes in ~10 Gyr. The circum-nuclear environment contains high density cold gas and associated star-formation. Major mergers are not the primary mechanism for transporting this gas inward; secular processes appear dominant. Stellar feedback will be generic in these objects and strong AGN feedback is seen only in the most powerful AGN. In Jet-Mode AGN the bulk of energetic output takes the form of collimated outflows (jets). These AGN are associated with the more massive black holes in more massive (classical) bulges and elliptical galaxies. Neither the accretion onto these black holes nor star-formation in their host bulge is significant today. These AGN are probably fueled by the accretion of slowly cooling hot gas that is limited by the feedback/heating provided by AGN radio sources. Surveys of the high-redshift universe are painting a similar picture. (Abridged).

• The paper shows that Radiative-Mode AGN operate in star-forming galaxies with pseudo-bulges and accretion rates above 1% of the Eddington limit.
• It demonstrates that Jet-Mode AGN in massive elliptical galaxies channel energy into radio jets, providing significant kinetic feedback.
• The study links dual AGN modes to distinct evolutionary paths, highlighting the roles of secular processes and AGN feedback in regulating galaxy growth.

Insights into the Co-Evolution of Galaxies and Supermassive Black Holes

The research paper "The Co-Evolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe," authored by Timothy M. Heckman and Philip N. Best, delivers a comprehensive exploration into the intertwined development of galaxies and their central supermassive black holes (SMBHs). This intricate relationship is elucidated through an overview of contemporary survey data, notably from the Sloan Digital Sky Survey (SDSS), with a focus on two distinct modes of active galactic nuclei (AGN) and their corresponding galaxy hosts—Radiative-Mode and Jet-Mode AGN.

Key Findings

The paper presents a categorical distinction between Radiative-Mode and Jet-Mode AGN based on energetic outputs and associated host galaxy types:

1. Radiative-Mode AGN: These are predominantly found in galaxies with pseudo-bulges, characterized by significant on-going star-formation and ample cold gas supply. This AGN mode operates with accretion rates above approximately 1% of the Eddington limit. The host galaxies typically have stellar masses between $10^{10.5}$ to $10^{11.5} M_\odot$, supporting an association with galaxies on the main star-forming sequence. Major mergers are considered not to be the primary gas transport mechanism, highlighting the importance of secular processes.
2. Jet-Mode AGN: Unlike their radiative counterparts, Jet-Mode AGN manifest predominantly in massive elliptical galaxies with classical bulges. These AGN function with low radiative efficiency, where the extracted energy is channeled into radio jets. The process is thought to involve accretion of gradually cooling hot gas, heavily moderated through AGN feedback mechanisms such as radio mode feedback.

Implications

The distinction between Radiative-Mode and Jet-Mode AGN underscores two paths of co-evolution shaped by mass, density, and environment:

• Radiative-Mode AGN: The prevalence of AGN in galaxies with substantial star formation underscores a strong link between black hole accretion and star-forming activities, where secular processes such as bar-driven inflows may dominate over more violent merger events. The high prevalence of radiative efficiencies supports a regime wherein black hole growth is synchronized with the growth of pseudo-bulges, perhaps eventually resulting in quenching star formation through AGN feedback during major outbursts.
• Jet-Mode AGN: These are seen as custodians of energy regulation in massive galaxies. The prevalent low accretion rates result in weaker radiative emissions but significant kinetic feedback through relativistic jets, broadly affecting the host galaxy’s hot gas. This feedback mechanism might play a crucial role in maintaining red-and-dead elliptical galaxies by preventing excessive cooling flows.

Future Developments

The paper suggests a continuity of these co-evolution processes in the high-redshift universe, supported by evidence of similar AGN structuring patterns in higher-redshift surveys. Future investigations are expected to integrate deeper multi-wavelength data, refining the understanding of the transition phases in AGN activity and their broader cosmological impact. Enhanced simulations that incorporate detailed physical processes in both star formation and AGN feedback at various epochs will further deepen the comprehension of galaxy and black hole co-evolution.

In conclusion, Heckman and Best's paper delineates a nuanced landscape of galactic co-evolution, framing AGN as pivotal regulatory elements within galaxies. This dual-mode AGN concept enriches the dialogue on galaxy evolution and highlights the essential role of SMBHs shaped by their environmental context throughout cosmic history. As high-sensitivity surveys become more prevalent, these findings lay a critical groundwork for unraveling the complexities of galaxy-AGN interactions across cosmic timescales.