A systematic study of AGN feedback in a disk galaxy I: global overview

Abstract

This is the first paper in a series using our MACER framework to investigate the evolution of a disk galaxy, which emphasizes the role of active galactic nucleus (AGN) feedback and incorporates cosmological inflows. This paper presents the model setup and the overall results. The predicted AGN duty cycle of approximately 0.49% is consistent with observations. Analysis of the AGN luminosity and star formation rate (SFR) light curves reveals a positive correlation between the two. We find that cold filaments condense in the circumgalactic medium (CGM) region due to radiative cooling and subsequently fall onto the galaxy, significantly enhancing both the SFR and AGN activity. The galaxy is then quenched over a timescale of approximately 1 Gyr by the strong feedback from the enhanced AGN activity. This indicates that a positive correlation between SFR and AGN luminosity does not preclude AGN feedback from acting as the quenching mechanism for the galaxy. Notably, models without AGN feedback exhibit significantly lower peak SFRs than those with it. We attribute this difference to cumulative AGN feedback, which drives gas from the galaxy into the CGM, facilitating the formation of more massive cold filaments and ultimately promoting more intense starburst episodes.

Figures (10)

• Figure 1: Initial conditions for the simulations: spatial distributions of the gas number density, temperature, and radial velocity. These fields are taken from the end of a 0.5625 Gyr relaxation run, during which the system evolves from the imposed initial setup toward an approximately hydrostatic configuration. We define this snapshot as $t = 0$ and adopt the resulting state as the starting point for all subsequent simulations.
• Figure 2: Time-averaged mass inflow rate in the inner region of the galaxy as a function of radius for various values of viscous parameter $\nu$. AGN feedback is turned off.
• Figure 3: Time evolution of the AGN luminosity, normalized to the Eddington luminosity ($L/L_{\mathrm{Edd}}$). From top to bottom, the panels correspond to $\nu = 0.25, 0.55$, $0.75$, and $1.1$. The dotted and dashed horizontal lines denote $0.01\,L_{\mathrm{Edd}}$ and $0.1\,L_{\mathrm{Edd}}$, respectively. In the Fiducial model, a notable increase in AGN luminosity occurs at $t \approx 7.8~\mathrm{Gyr}$. An inspection of the simulation movie indicates that this rise is a direct consequence of substantial cold filaments that formed earlier in the galaxy’s CGM. These filaments subsequently traverse the ISM and are ultimately accreted onto the black hole, triggering AGN activity and enhancing the luminosity.
• Figure 4: Time evolution of the AGN luminosity, normalized to the Eddington luminosity ($L/L_{\mathrm{Edd}}$), for the Fiducial run (top) and the ModelLow run (bottom). The dotted and dashed horizontal lines denote $0.01\,L_{\mathrm{Edd}}$ and $0.1\,L_{\mathrm{Edd}}$, respectively.
• Figure 5: Time evolution of the star formation rate (SFR, top) and specific star formation rate (sSFR, bottom) in various models. The dotted horizontal line marks the quenching threshold; values below this line indicate that the galaxy is quenched. The peak at $\sim$ 8Gyr in the Fiducial model arises from the same physical origin with the peak of AGN luminosity shown in Fig. \ref{['fig:AGNlightcurve']}, i.e., the formation of cold filaments in the CGM and their subsequent infall onto the galaxy. The galaxy in the Fiducial model is quenched within $\sim 1$ Gyr by the AGN feedback.