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Regulation of AGN power in the fiducial MPG simulation. The top row of panels shows how the varying radial distribution of radiative losses (L rad˜, rad˜rad˜, colored lines) compares with the constant radial distribution of stellar power input (P ˜ * , blue dashed line). For clarity, the 1.5 Gyr time period of the simulation is broken into three subperiods as labeled, with lines showing the radial distribution of L radãt radãt 50 Myr intervals. The lower two panels show how both radiative losses (L rad ) from the central 3 kpc and jet power (P jet ) compare with stellar power input within 3 kpc (P SNIa ∼ 4.34 × 10 40 erg s −1 ) during the time period of the simulation. A strong initial outburst of AGN power lowers the atmospheric density at r < 15 kpc during the first 250 Myr, until SNIa power input exceeds radiative losses from ∼0.3 to 3 kpc. During the middle subperiod (0.5-1.1 Gyr), radiative losses slowly rise as atmospheric density within 10 kpc slowly increases. Shortly after 1.1 Gyr, radiative losses once again exceed stellar power input, resulting in another powerful AGN outburst that again pushes radiative losses below stellar power input at r 3 kpc by t = 1.5 Gyr.
Source publication
Coupling between active galactic nuclei (AGNs) and the circumgalactic medium (CGM) is critical to the interplay between radiative cooling and feedback heating in the atmospheres of the universe’s most massive galaxies. This paper presents a detailed analysis of numerical simulations showing how kinetic AGN feedback with a strong momentum flux inter...
Contexts in source publication
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... the AGN power does not substantially alter the structure of the galaxy's atmosphere in that region. Figure 5 shows how AGN self-regulation proceeds in the fiducial MPG simulation. As in Figure 4, three panels across Figure 3. Evolution of the initial outburst in the fiducial MPG simulation, starting at t = 10 Myr, shortly after the AGN outburst begins and proceeding through the time when the initial shock front is propagating through the galaxy (t = 30 Myr) to the time when stellar heating starts to exceed radiative cooling within the galaxy (t = 270 Myr). ...
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... low entropy during this period of high AGN power results from assumptions built into the feedback algorithm, which specifies that the total energy of ejected gas is 10 −4 times the rest-mass energy, with 90% in kinetic form and 10% in thermal form. When AGN power is high, the mass flow of the jets (equal to M acc by design) is also high, resulting in Temporary excursions to very high jet power (see the gray line in Figure 5) therefore can cause the jet material to have a low entropy level. The entropy of that outflowing gas does not remain low for very long, because it soon passes at high speed through a reverse shock, gaining more entropy, as shown in Figure 12. ...
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... 250 Myr, those low-entropy outflows are gone. But before they go, they produce a prominent luminosity spike, peaking near 220 Myr in Figure 5. The luminosity peaks when the density of gas that has just passed through the reverse shock is greatest. ...
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... is the time period during which large-scale circulation transports higherentropy gas from larger radii into the central 10 kpc along directions approximately perpendicular to the jet axis. That rise in entropy lowers the atmospheric density and pressure surrounding the galaxy, enabling SNIa heating to exceed radiative cooling within the central 3 kpc during the same time period (see Figure 5). As in the fiducial SPG simulation, not much shock heating is evident outside of the jet cone. ...
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... 500 Myr, while AGN power is low, the atmospheric circulation pattern changes as shown in Figures 14 and 15. Lower-entropy gas that circulation has transported upward along the polar axis is no longer being suspended there by a strong outflow. ...
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... periods of strong feedback come to an end when the central gas density has dropped enough for stellar heating to exceed radiative cooling within the central few kiloparsecs. Then the simulations enter a lowpower mode in which less powerful AGN outbursts allow stellar heating to maintain a nearly steady state within the galaxy (see Figures 4 and 5), consistent with the black hole feedback valve scenario of Voit et al. (2020). ...
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... colored curves in the top panel of Figure 17 show that ram pressure in the fiducial SPG simulation drops below the median gas pressure after about 200 Myr. That drop corresponds to a concurrent decline in jet power by an order of magnitude (see Figure 5). As a result, the weaker outbursts characteristic of the low-power feedback mode do not have a great enough momentum flux to drill much beyond 10 kpc. ...
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... colored curves in the middle panel of Figure 17 show that ram pressure in the fiducial MPG simulation eventually drops below the median gas pressure after about 400 Myr, also corresponding to a large drop in AGN power (see Figure 5). In this case, a power decline of roughly two orders of magnitude Figure 13. ...
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... natural cooling rate of the MPG atmosphere (with K/r ≈ 1.2 keV cm 2 kpc −1 ) is much greater and results in far more AGN power, at least at the outset. For the initial MPG entropy profile, the natural cooling rate is (see Figure 5). ...
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... as discussed in Section 3.4, the formerly stellar gas swept out of the galaxy accumulates in the CGM at 30-100 kpc from the center, causing a slow rise in CGM pressure. In the fiducial MPG simulation, that slow rise in pressure forces the gas density to rise and entropy to drop at 1 kpc, causing radiative cooling to exceed stellar heating there at 1.1 Gyr (see Figure 5). AGN fueling is once again coupled to the natural cooling-flow rate at larger radii, initiating a second episode of strong AGN feedback and large-scale circulation. ...
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Citations
... This effect is caused by substantial (ICM) gas outflows driven by the jet and the subsequent rising of the lobe (not explicitly shown here, but see e.g. Chen et al. 2019;Prasad et al. 2022). ...
Feedback driven by jets from active galactic nuclei is believed to be responsible for reducing cooling flows in cool-core galaxy clusters. We use simulations to model feedback from hydrodynamic jets in isolated halos. While the jet propagation converges only after the diameter of the jet is well resolved, reliable predictions about the effects these jets have on the cooling time distribution function only require resolutions sufficient to keep the jet-inflated cavities stable. Comparing different model variations, as well as an independent jet model using a different hydrodynamics code, we show that the dominant uncertainties are the choices of jet properties within a given model. Independent of implementation, we find that light, thermal jets with low momentum flux tend to delay the onset of a cooling flow more efficiently on a $50$ Myr timescale than heavy, kinetic jets. The delay of the cooling flow originates from a displacement and boost in entropy of the central gas. If the jet luminosity depends on accretion rate, collimated, light, hydrodynamic jets are able to reduce cooling flows in halos, without a need for jet precession or wide opening angles. Comparing the jet feedback with a `kinetic wind' implementation shows that equal amounts of star formation rate reduction can be achieved by different interactions with the halo gas: the jet has a larger effect on the hot halo gas while leaving the denser, star forming phase in place, while the wind acts more locally on the star forming phase, which manifests itself in different time-variability properties.
... Ho we ver, once the bo w shock has cut a path through the ambient core, there would not be a significant continued supply of energy if the flow pattern becomes stationary. Prasad, Voit & O'Shea ( 2022 ) show that taking a narrow jet opening angle reduces the thrust per unit area and so increases the long-term coupling with the ambient gas. The simulations presented here allow us to quantify the amount of energy that may aid the support of the inner core. ...
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