XMAGNET : Kinetic, Thermal and Magnetic AGN Feedback in Massive Galaxies at Halo Masses $\sim 10^{13.5}$ M$_\odot$

TL;DR

This work investigates how magnetised AGN feedback interacts with the circumgalactic medium in halos around $M_{200}\sim10^{13.5}\,M_\odot$, comparing multiphase and single-phase CGM states. Using magnetohydrodynamic simulations with the AthenaPK code, seed $1\,\mu$G magnetic fields, and variable energy partitioning among kinetic, thermal, and magnetic channels, the authors find that pure kinetic feedback best prevents catastrophic CGM cooling while maintaining observed entropy, whereas allocating part of the energy to thermal channels creates an inner entropy bump and can promote extended cold gas. Magnetic fields tend to collimate jets and sustain higher core entropy, constraining cold gas to smaller radii and modulating the AGN duty cycle. In higher-density, higher-pressure SPG-Cool halos, feedback struggles to erase the MPG-like CGM, implying that halo assembly history or mergers may be necessary to reach SPG-like atmospheres. Overall, the results highlight the critical roles of energy partitioning and magnetic fields in shaping CGM thermodynamics and the cold-gas distribution in massive galaxies.

Abstract

The interplay between radiative cooling of the circumgalactic medium (CGM) and feedback heating governs the evolution of the universe's most massive galaxies. This paper presents simulations of feedback processes in massive galaxies showing how kinetic, thermal, and magnetic active galactic nuclei (AGN) feedback interacts with the CGM under different environmental conditions. We find that in massive galaxies with shallower central gravitational potential and higher CGM pressure (multiphase galaxy; MPG) pure kinetic AGN feedback is most efficient in preventing CGM cooling from becoming catastrophic while maintaining the CGM entropy within the observed range. For the same galaxy, partitioning AGN energy injection into kinetic ($75\%$) and thermal ($25\%$) energy results in an entropy bump within $r\lesssim15$ kpc while also having a larger amount of cold gas extending out to $r\sim80$ kpc. A magnetohydrodynamic MPG run with seed magnetic field in the CGM (1~$μ$G) and partial magnetised AGN feedback ($1\%$ of total AGN power) also shows a higher entropy (within $r<15$ kpc) and cold gas mass, albeit the cold gas remains constrained within $r\lesssim30$ kpc. For a similarly massive galaxy with deeper potential well and low CGM pressure (single phase galaxy; SPG) our simulations show that for both hydro and MHD runs with partial thermal AGN energy, the feedback mechanism remains tightly self-regulating with centrally concentrated cooling (within $r<1$ kpc). Our simulations of a similar mass galaxy with a deeper potential well and higher CGM pressure (SPG-Cool) show that our AGN feedback mechanism cannot get rid of the high CGM density and pressure and its long term evolution is similar to the multiphase galaxy.

Figures (17)

• Figure 1: Radial electron density ( top left panel), pressure ( top right panel), entropy ( bottom left panel) and cooling time ( bottom right panel) profile for the MPG (blue line), SPG (red line) and SPG-Cool (black line) runs at $t=0$. The baryon profile of the SPG-Cool halo is closer to the MPG halo.
• Figure 2: Jet power ($P_{\rm jet}$; red line) and cold gas mass (blue line), total stellar mass (M$_\star$; green line) and X-ray luminosity for the $0.5-7$ keV gas within central $r\lesssim50$ kpc (black line) with time for the MPG-hydro-kinetic run (bottom panel), MPG-hydro run (middle panel) and MPG-MHD run (top panel). Note the higher $P_{\rm jet}$ ($<P_{\rm jet}>\sim 5.6\times10^{44}$ erg s$^{-1}$) and lower $M_{\rm cold}$ for the pure kinetic AGN feedback run compared to MPG-hydro ($<P_{\rm jet}>\sim 3.9\times10^{43}$ erg s$^{-1}$) and MPG-MHD ($<P_{\rm jet}>\sim 4.2\times10^{44}$ erg s$^{-1}$) runs.
• Figure 3: Top Left panel : Median mass-weighted radial entropy profile for the X-ray gas ($0.2$ keV $< T < 8$ keV) for MPG-MHD (blue line), MPG-hydro (red line) and MPG-hydro-kinetic (black line) runs. The faded cyan, red and grey region represent the 5th-95th percentile range of radial entropy profile at each radius between $t=0.5-1.5$ Gyr for the MHD, hydro and hydro-kinetic MPG runs respectively. Top Right panel : Median mass-weighted radial $t_{\rm cool}$ for the multiphase galaxy MPG-MHD (solid blue line), MPG-hydro (red line) and MPG-hydro-kinetic (black line) runs. Bottom left panel : Median plasma-$\beta$ ($=P/[B^2/2\mu_0]$) for the MPG-MHD run (solid blue line) with the shaded region showing the spread of plasma-$\beta$ between 5th to 95th percentile at each radii. Bottom right panel : Angle-averaged radial B-field at different times for the MPG-MHD run. The color of the lines show the time of the radial profile between t = 0-2 Gyr with a cadence of 100 Myr.
• Figure 4: SNIa heating to radiative cooling ratio for the MPG-MHD (left panel), MPG-hydro (middle panel) and MPG-hydro-kinetic (right panel) runs between t = 0 - 1.5 Gyr with a cadence of 100 Myr. The color of the lines represents the time of the galaxy evolution. For the MPG-hydro and MPG-MHD runs, SNIa heating remains dominant over cooling within the central $r\lesssim5$ kpc while for MPG-hydro-kinetic run cooling dominates over heating.
• Figure 5: Jet power ($P_{\rm jet}$; red line) and cold gas mass (blue line), total stellar mass (M$_\star$; green line) and X-ray luminosity for the $0.5-7$ keV within the central $r = 50$ kpc (black line) with time for the SPG-MHD (left panel) and the SPG-hydro run (right panel). While both runs show similar AGN behaviour with ($<P_{\rm jet}>\sim1.5\times 10^{42}$ erg s$^{-1}$), the number of AGN cycles is higher for the SPG-MHD run compared to SPG-hydro run.