Abstract
ABSTRACT Without additional heating, radiative cooling of the halo gas of massive galaxies (Milky Way-mass and above) produces cold gas or stars exceeding that observed. Heating from active galactic nucleus (AGN) jets is likely required, but the jet properties remain unclear. This is particularly challenging for galaxy simulations, where the resolution is orders-of-magnitude insufficient to resolve jet formation and evolution. On such scales, the uncertain parameters include the jet energy form [kinetic, thermal, cosmic ray (CR)]; energy, momentum, and mass flux; magnetic fields; opening angle; precession; and duty cycle. We investigate these parameters in a $10^{14}\, {\rm M}_{\odot }$ halo using high-resolution non-cosmological magnetohydrodynamic simulations with the FIRE-2 (Feedback In Realistic Environments) stellar feedback model, conduction, and viscosity. We explore which scenarios qualitatively meet observational constraints on the halo gas and show that CR-dominated jets most efficiently quench the galaxy by providing CR pressure support and modifying the thermal instability. Mildly relativistic (∼MeV or ∼1010K) thermal plasma jets work but require ∼10 times larger energy input. For fixed energy flux, jets with higher specific energy (longer cooling times) quench more effectively. For this halo mass, kinetic jets are inefficient at quenching unless they have wide opening or precession angles. Magnetic fields also matter less except when the magnetic energy flux reaches ≳ 1044 erg s−1 in a kinetic jet model, which significantly widens the jet cocoon. The criteria for a successful jet model are an optimal energy flux and a sufficiently wide jet cocoon with a long enough cooling time at the cooling radius.
Highlights
A major outstanding problem in galaxy formation for decades has been how to ‘quench’ massive galaxies and keep them ‘red and dead’ over a large fraction of cosmic time
We found that turbulent stirring within a radius of order the halo scale radius, or cosmic ray (CR) injection were able to maintain a stable, CC, low-star formation rates (SFRs) halo for extended periods, across haloes with mass 1012−1014 M, without obviously violating observational constraints on halo gas properties or exceeding plausible energy budgets for low luminosity active galactic nucleus (AGN) in massive galaxies
We did not attempt to model realistic jets or AGN outflows; instead, we intentionally considered energy input or ‘stirring’ rates distributed according to an arbitrary spatial kernel, without considering how that energy would propagate from a collimated geometry, or how turbulence would be produced
Summary
A major outstanding problem in galaxy formation for decades has been how to ‘quench’ massive galaxies (stellar masses 1011 M or above ∼L∗ in the galaxy luminosity function) and keep them ‘red and dead’ over a large fraction of cosmic time (see e.g. Bell et al 2003; Kauffmann et al 2003; Madgwick et al 2003; Baldry et al 2004; Blanton et al 2005; Kereset al. 2005; Dekel & Birnboim 2006; Kereset al. 2009; Pozzetti et al 2010; Wetzel, Tinker & Conroy 2012; Feldmann & Mayer 2015; Voit et al 2015). Bell et al 2003; Kauffmann et al 2003; Madgwick et al 2003; Baldry et al 2004; Blanton et al 2005; Kereset al. The heating must still preserve the cool core structure (e.g. density and entropy profiles) observed in the majority of galaxies (Peres et al 1998; Mittal et al 2009). One way to achieve this is to suppress the cooling flow and maintain a very-low SFR, stable cool-core (CC) cluster. Another possibility is that clusters undergo cool-core–non-cool-core (NCC) cycles: a stronger episode of feedback overturns the cooling flows, resulting in a NCC cluster that gradually recovers to a CC cluster and starts another episode of feedback
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