Active Galactic Nuclei Feedback in an Elliptical Galaxy with the Most Updated AGN Physics (I): Low-angular Momentum Case (1712.04964v2)

Abstract: We investigate the effects of AGN feedback on the cosmological evolution of an isolated elliptical galaxy by performing two-dimensional high-resolution hydrodynamical numerical simulations. The inner boundary of the simulation is chosen so that the Bondi radius is resolved. Compared to previous works, the two accretion modes, namely hot and cold, which correspond to different accretion rates and have different radiation and wind outputs, are carefully discriminated and the feedback effects by radiation and wind in each mode are taken into account. The most updated AGN physics, including the descriptions of radiation and wind from the hot accretion flows and wind from cold accretion disks, are adopted. Physical processes like star formation, Type Ia and Type II supernovae are taken into account. We study the AGN light curve, typical AGN lifetime, growth of the black hole mass, AGN duty-cycle, star formation, and the X-ray surface brightness of the galaxy. We compare our simulation results with observations and find general consistency. Comparisons with previous simulation works find significant differences, indicating the importance of AGN physics. The respective roles of radiation and wind feedbacks are examined and it is found that they are different for different problems of interest such as AGN luminosity and star formation. We find that it is hard to neglect any of them, so we suggest to use the names of "cold feedback mode" and "hot feedback mode" to replace the currently used ones.

An In-Depth Analysis of AGN Feedback in Elliptical Galaxies

The paper "Active Galactic Nuclei Feedback in an Elliptical Galaxy with the most updated AGN physics (I): low-angular momentum case" by Feng Yuan et al. investigates the impact of Active Galactic Nuclei (AGN) feedback on the evolution of an isolated elliptical galaxy. The paper employs two-dimensional hydrodynamical simulations to provide a detailed examination of AGN feedback mechanisms using the latest advancements in AGN physics. The paper is structured into diverse sections, which thoroughly explore different aspects of AGN feedback, including its effects on the host galaxy's gas and star formation, as well as the implications for black hole growth.

Overview of AGN Feedback Mechanisms

A notable aspect of this research is the implementation of updated AGN physics, particularly concerning the radiation and wind emissions from both cold and hot accretion flows. The two accretion modes, cold and hot, are analyzed separately, each giving rise to distinct feedback mechanisms within the galaxy. Cold accretion corresponds to higher accretion rates and is typically associated with high-luminosity AGNs, while hot accretion is found in low-luminosity AGNs.

The authors propose using the terminology "cold feedback mode" and "hot feedback mode" in place of the often misleading existing terms such as quasar and radio modes, highlighting the role of both radiation and wind within each accretion mode. Their findings demonstrate that wind feedback is more effective than radiative feedback in suppressing black hole growth and star formation due to its ability to impart momentum more locally to the interstellar medium (ISM).

Simulation Insights and Comparisons

The paper presents detailed simulations that resolve the Bondi radius, allowing precise determination of AGN accretion rates. By analyzing several feedback models, namely full feedback (fullFB), wind feedback (windFB), radiative feedback (radFB), and no feedback (noFB), Yuan et al. compare their findings with previous models, emphasizing significant differences due to refined AGN physics.

The paper reports that the AGN's activity tends to fluctuate significantly once feedback mechanisms are included, driven by intermittent star formation facilitated by AGN-induced structures in the galaxy's ISM. The AGN variability often includes phases of strong activity interspersed with quiescence, reflecting observed AGN behavior.

Key Results and Implications

Key findings include the pronounced variability of AGN light curves, which are dominantly controlled by wind feedback. The paper concludes that wind feedback effectively reduces the AGN's accretion rate, highlighted by a stark contrast between the windFB and radFB models. Also, the predicted AGN lifetime aligns well with observational data, estimated at approximately $10^5$ years.

The researchers explore the impact of AGN feedback on star formation, identifying a dual effect: negative feedback suppressing star formation in central regions and positive feedback potentially enhancing it in outer regions due to AGN-driven gas redistribution. These insights underscore the complex nature of AGN feedback, contributing to both galaxy evolution and black hole growth. The simulated AGN duty cycle also points out that AGNs spend most of their time in a low-luminosity state, which supports dark matter and ISM dynamics theories that suggest low accretion rates predominately modulate galaxy evolution over cosmic timescales.

Future Directions

Future investigations could expand this paper by incorporating higher-angular momentum cases or modeling external accretion from cosmic structures. As the feedback processes are highly sensitive to initial conditions, incorporating more realistic galactic environments might improve the predictiveness of such simulations. The researchers also emphasize the need to explore jet feedback, given the jets' potential impact on galaxy clusters despite their relative insignificance for isolated galaxies.

This paper significantly advances the understanding of AGN feedback by meticulously integrating contemporary findings from accretion physics into simulation models. While offering relevant predictions broadly aligned with observations, there remains potential for further exploration in multi-galaxy setups and adaptive resolution techniques for even finer feedback process simulations.