A systematic study of AGN feedback in a disk galaxy II: MACER prediction of X-ray surface brightness profile and comparison with eROSITA observations

Abstract

Recently, we have performed a systematic study of AGN feedback in a disk galaxy within the MACER framework. Various model predictions, including the AGN duty cycle, the correlation between black hole accretion rates and star formation rates, and the (cold) gas fraction, have been compared with observations and will be presented in a series of papers. As the second paper in this series, without adjusting any model parameters, we directly use the simulation data introduced in Paper I to compute the predicted X-ray surface brightness profile and compare it with eROSITA observations of circumgalactic medium (CGM) emission around galaxies, which provide important constraints on AGN feedback models. For this comparison, we adopt two stacked eROSITA radial profiles of X-ray surface brightness: (1) distant galaxies with log(M*/M_sun) = 10.5-11.0 at z ~ 0.02-0.10 from Y. Zhang et al. (2024), and (2) nearby L* galaxies within 50 Mpc from L. He & Z. Li (2026). We find that the average simulated profile over time is in good agreement with the stacked measurements of Y. Zhang et al. (2024) over a broad radial range (out to ~ 100 kpc). Our model predictions also match the results of L. He & Z. Li (2026) at projected radii from ~ 20 kpc to 120 kpc. Overall, the consistency between our simulations and the eROSITA data indicates that the X-ray emission detected by eROSITA is predominantly thermal in origin, rather than nonthermal, as supported by the spectral analysis presented by L. He & Z. Li (2026).

Figures (5)

• Figure 1: Simulated versus observed CGM X-ray surface-brightness profiles as a function of projected radius. Left: Purple points (with error bars) show the stacked profile of Milky Way-mass galaxies from Zhang2024a (median distance $\sim$320 Mpc). Gold curves and shaded bands show predictions of the Fiducial model from Zou_2026 for three gas metallicities: dashed, solid, and dotted lines correspond to $Z=0.02\,Z_\odot$, $0.3\,Z_\odot$, and $0.5\,Z_\odot$, respectively. For $Z=0.3\,Z_\odot$, the solid curve denotes the mean profile, and the shaded regions enclose the central 10%, 50%, and 90% percentile ranges. Right: Black squares show the stacked profile from he2026; median distance $\sim$36 Mpc. Because their count-rate--to--flux conversion assumes solar metallicity, we show the simulation only for $Z=1.0\,Z_\odot$. The green solid curve is the mean Fiducial prediction, with shaded regions indicating the central 10%, 50%, and 90% percentile ranges. The simulated profile is convolved with the same angular PSF as in the left panel and rescaled to the physical scale appropriate for the closer median distance.
• Figure 2: Comparison between simulated and observed stacked X-ray surface brightness profiles of the CGM around Milky Way-mass galaxies. Left: Purple points with error bars show the stacked X-ray surface brightness profile from Zhang2024a, whose observational sample has a median distance of $\sim$320 Mpc. The simulated profiles are convolved with the same angular PSF, corresponding to this median distance. Right: Black squares show the stacked CGM X-ray surface brightness profile from He & Li (2025), with a median sample distance of $\sim$36 Mpc. The simulated profiles are convolved with the same angular PSF, but rescaled to the closer median distance. In both panels, the green solid line shows the mean profile of our Fiducial model, while the green dashed line shows the mean profile of the Fiducial_3 model, in which the initial CGM gas mass is three times that of the Fiducial model.
• Figure 3: Time evolution of the total circumgalactic medium (CGM) gas mass in the simulations. Left: Total gas mass enclosed within 30--250 kpc. Right: Total gas mass enclosed within 30--400 kpc. All gas masses are shown in units of solar masses. In both panels, the green curve corresponds to the Fiducial model, while the blue curve represents the Fiducial_3 model, in which the initial CGM gas mass is increased by a factor of three relative to the Fiducial model.
• Figure 4: Comparison of simulated and observed CGM X-ray surface brightness profiles. Left: Purple points with error bars show the stacked X-ray surface brightness profile of Milky Way-mass galaxies from Zhang2024a. Solid gold and dashed blue curves represent the mean predictions of the Fiducial and noAGN models, respectively; shaded bands mark the central 10% percentile ranges. Right: Black squares show the stacked CGM X-ray surface brightness profile from he2026. Solid green and dashed blue curves represent the mean predictions of the Fiducial and noAGN models, respectively, with shading again indicating the central 10% percentile ranges. The comparison underscores the significant role of AGN feedback in shaping the CGM X-ray emission.
• Figure 5: Time-averaged radial profiles of CGM gas properties. Left: Gas number density profile. Middle: Gas temperature profile. Right: Gas entropy profile. In all panels, the green solid curve corresponds to the Fiducial model, while the blue dashed curve represents the noAGN model.