AGN feedback, quiescence and CGM metal enrichment in early-type galaxies

We present three-dimensional hydrodynamical simulations showing the effect of kinetic and radiative AGN feedback on a model galaxy representing a massive quiescent low-redshift early-type galaxy of $M_* = 8.41\times 10^{10} M_\odot$, harbouring a $M_\mathrm{BH} = 4\times 10^8 M_\odot$ black hole surrounded by a cooling gaseous halo. We show that, for a total baryon fraction of $\sim 20\%$ of the cosmological value, feedback from the AGN can keep the galaxy quiescent for about 4.35 Gyr and with properties consistent with black hole mass and X-ray luminosity scaling relations. However, this can only be achieved if the AGN feedback model includes both kinetic and radiative feedback modes. The simulation with only kinetic feedback fails to keep the model galaxy fully quiescent, while one with only radiative feedback leads to excessive black-hole growth. For higher baryon fractions (e.g. 50\% of the cosmological value), the X-ray luminosities exceed observed values by at least one order of magnitude, and rapid cooling results in a star-forming galaxy. The AGN plays a major role in keeping the circumgalactic gas at observed metallicities of $Z/Z_\odot \gtrsim 0.3$ within the central $\sim 30$ kpc by venting nuclear gas enriched with metals from residual star formation activity. As indicated by previous cosmological simulations, our results are consistent with a model for which the black hole mass and the total baryon fraction are set at higher redshifts $z > 1$ and the AGN alone can keep the model galaxy on observed scaling relations. Models without AGN feedback violate both the quiescence criterion as well as CGM metallicity constraints.Comment: 19 pages, 15 figures. Accepted for publication in MNRA

Momentum Driving: which physical processes dominate AGN feedback?

The deposition of mechanical feedback from a supermassive black hole (SMBH) in an active galactic nucleus (AGN) into the surrounding galaxy occurs via broad-line winds which must carry mass and radial momentum as well as energy. The effect can be summarized by the dimensionless parameter $\eta=dot{M_outflow}/dot{M_accretion}= (2 \epsilon_w c^2)/v_w^2$ where (\epslion_w \equiv dot{E}_w/(dot{M_accretion} c^2)) is the efficiency by which accreted matter is turned into wind energy in the disc surrounding the central SMBH. The outflowing mass and omentum are proportional to $\eta$, and many prior treatments have essentially assumed that $\eta=0$. We perform one- and two-dimensional simulations and find that the growth of the central SMBH is very sensitive to the inclusion of the mass and momentum driving but is insensitive to the assumed mechanical efficiency. For example in representative calculations, the omission of momentum and mass feedback leads to an hundred fold increase in the mass of the SMBH to over 10^{10} \Msun. When allowance is made for momentum driving, the final SMBH mass is much lower and the wind efficiencies which lead to the most observationally acceptable results are relatively low with $\epsilon_w \lesssim 10^{-4}$.Comment: 10 pages, 8 figures, resubmitted to ApJ, added reference

The Role of Black Hole Feedback on Size and Structural Evolution in Massive Galaxies

We use cosmological hydrodynamical simulations to investigate the role of feedback from accreting black holes on the evolution of sizes, compactness, stellar core density and specific star-formation of massive galaxies with stellar masses of $M_{star} > 10^{10.9} M_{\odot}$. We perform two sets of cosmological zoom-in simulations of 30 halos to z=0: (1) without black holes and Active Galactic Nucleus (AGN) feedback and (2) with AGN feedback arising from winds and X-ray radiation. We find that AGN feedback can alter the stellar density distribution, reduce the core density within the central 1 kpc by 0.3 dex from z=1, and enhance the size growth of massive galaxies. We also find that galaxies simulated with AGN feedback evolve along similar tracks to those characterized by observations in specific star formation versus compactness. We confirm that AGN feedback plays an important role in transforming galaxies from blue compact galaxies into red extended galaxies in two ways: (1) it effectively quenches the star formation, transforming blue compact galaxies into compact quiescent galaxies and (2) it also removes and prevents new accretion of cold gas, shutting down in-situ star formation and causing subsequent mergers to be gas-poor or mixed. Gas poor minor mergers then build up an extended stellar envelope. AGN feedback also puffs up the central region through the fast AGN driven winds as well as the slow expulsion of gas while the black hole is quiescent. Without AGN feedback, large amounts of gas accumulate in the central region, triggering star formation and leading to overly massive blue galaxies with dense stellar cores.Comment: 13 pages, 7 figures, Accepted for publication in Ap

The impact of mechanical AGN feedback on the formation of massive early-type galaxies

We employ cosmological hydrodynamical simulations to investigate the effects of AGN feedback on the formation of massive galaxies with present-day stellar masses of $M_{stel} = 8.8 \times 10^{10} - 6.0 \times 10^{11} M_{sun}$. Using smoothed particle hydrodynamics simulations with a pressure-entropy formulation that allows an improved treatment of contact discontinuities and fluid mixing, we run three sets of simulations of 20 halos with different AGN feedback models: (1) no feedback, (2) thermal feedback, and (3) mechanical and radiation feedback. We assume that seed black holes are present at early cosmic epochs at the centre of emerging dark matter halos and trace their mass growth via gas accretion and mergers with other black holes. Both feedback models successfully recover the observed M_BH - sigma relation and black hole-to-stellar mass ratio for simulated central early-type galaxies. The baryonic conversion efficiencies are reduced by a factor of two compared to models without any AGN feedback at all halo masses. However, massive galaxies simulated with thermal AGN feedback show a factor of ~10-100 higher X-ray luminosities than observed. The mechanical/radiation feedback model reproduces the observed correlation between X-ray luminosities and velocity dispersion, e.g. for galaxies with sigma = 200 km/s, the X-ray luminosity is reduced from $10^{42}$ erg/s to $10^{40}$ erg/s. It also efficiently suppresses late time star formation, reducing the specific star formation rate from $10^{-10.5}$ $yr^{-1}$ to $10^{-14}$ $yr^{-1}$ on average and resulting in quiescent galaxies since z=2, whereas the thermal feedback model shows higher late time in-situ star formation rates than observed.Comment: 13 pages, 11 figures, accepted for the publication in MNRA

Consequences of Mechanical and Radiative Feedback from Black Holes in Disc Galaxy Mergers

We study the effect of AGN mechanical and radiation feedback on the formation of bulge dominated galaxies via mergers of disc galaxies. The merging galaxies have mass-ratios of 1:1 to 6:1 and include pre-existing hot gaseous halos to properly account for the global impact of AGN feedback. Using smoothed particle hydrodynamics simulation code (GADGET-3) we compare three models with different AGN feedback models: (1) no black hole and no AGN feedback; (2) thermal AGN feedback; and (3) mechanical and radiative AGN feedback. The last model is motivated by observations of broad line quasars which show winds with initial velocities of $v_w \ge$ 10,000 km/s and also heating associated with the central AGN X-ray radiation. The primary changes in gas properties due to mechanical AGN feedback are lower thermal X-ray luminosity from the final galaxy - in better agreement with observations - and galactic outflows with higher velocity $\sim 1000$ km/s similar to recent direct observations of nearby merger remnants. The kinetic energy of the outflowing gas is a factor of $\sim$ 20 higher than in the thermal feedback case. All merger remnants with momentum-based AGN feedback with $v_w \sim 10,000$ km/s and $\epsilon_w=2 \times 10^{-3}$, independent of their progenitor mass-ratios, reproduce the observed relations between stellar velocity dispersion and black hole mass ($M_{\rm bh} - \sigma$) as well as X-ray luminosity ($L_X - \sigma$) with $10^{37.5}$ erg/s $\lesssim L_X (0.3-8~{\rm keV}) \lesssim 10^{39.2}$ erg/s for velocity dispersions in the range of 120 km/s $\lesssim \sigma \lesssim$ 190 km/s. In addition, the mechanical feedback produces a much greater AGN variability. We also show that gas is more rapidly and impulsively stripped from the galactic centres driving a moderate increase in galaxy size and decrease in central density with the mechanical AGN feedback model.Comment: 16 pages, 10 figures, resubmitted to MNRA

The Impact of Outflows driven by Active Galactic Nuclei on Metals in and around Galaxies

Metals in the hot gaseous halos of galaxies encode the history of star formation as well as the feedback processes that eject metals from the galaxies. X-ray observations suggest that massive galaxies have extended distributions of metals in their gas halos. We present predictions for the metal properties of massive galaxies and their gaseous halos from recent high resolution zoom-in simulations that include mechanical and radiation driven feedback from Active Galactic Nuclei (AGN). In these simulations, AGN launch high-velocity outflows, mimicking observed broad absorption line winds. By comparing two sets of simulations with and without AGN feedback, we show that our prescription for AGN feedback is capable of driving winds and enriching halo gas `inside-out' by spreading centrally enriched metals to the outskirts of galaxies, into the halo and beyond. The metal (iron) profiles of halos simulated with AGN feedback have a flatter slope than those without AGN feedback, consistent with recent X-ray observations. The predicted gas iron abundance of group scale galaxies simulated with AGN feedback is $Z_{\rm Fe} = 0.23$ $Z_{\rm Fe,\odot}$ at $0.5 r_{500}$, which is 2.5 times higher than that in simulations without AGN feedback. In these simulations, AGN winds are also important for the metal enrichment of the intergalactic medium, as the vast majority of metals ejected from the galaxy by AGN-driven winds end up beyond the halo virial radius.Comment: Accepted for publication in ApJ. 16 pages, 9 figures. Key figures are 8 &

Linking galaxy structural properties and star formation activity to black hole activity with IllustrisTNG

We study the connection between active galactic nuclei (AGN) and their host galaxies through cosmic time in the large-scale cosmological IllustrisTNG simulations. We first compare BH properties, i.e. the hard X-ray BH luminosity function, AGN galaxy occupation fraction, and distribution of Eddington ratios, to available observational constraints. The simulations produce a population of BHs in good agreement with observations, but we note an excess of faint AGN in hard X-ray (L_x ~ 10^{43-44} erg/s), and a lower number of bright AGN (L_x>10^{44} erg/s), a conclusion that varies quantitatively but not qualitatively with BH luminosity estimation method. The lower Eddington ratios of the 10^{9} Msun BHs compared to observations suggest that AGN feedback may be too efficient in this regime. We study galaxy star formation activity and structural properties, and design sample-dependent criteria to identify different galaxy types (star-forming/quiescent, extended/compact) that we apply both to the simulations and observations from the candels fields. We analyze how the simulated and observed galaxies populate the specific star formation rate - stellar mass surface density diagram. A large fraction of the z=0 M_{star}>10^{11} Msun quiescent galaxies first experienced a compaction phase (i.e. reduction of galaxy size) while still forming stars, and then a quenching event. We measure the dependence of AGN fraction on galaxies' locations in this diagram. After correcting the simulations with a redshift and AGN luminosity-dependent model for AGN obscuration, we find good qualitative and quantitative agreement with observations. The AGN fraction is the highest among compact star-forming galaxies (16-20% at z~1.5-2), and the lowest among compact quiescent galaxies (6-10% at z~1.5-2).Comment: 35 pages, 22 figures, accepted for publication in MNRA

The impact of AGN on stellar kinematics and orbits in simulated massive galaxies

We present a series of 20 cosmological zoom simulations of the formation of massive galaxies with and without a model for AGN feedback. Differences in stellar population and kinematic properties are evaluated by constructing mock integral field unit (IFU) maps. The impact of the AGN is weak at high redshift when all systems are mostly fast-rotating and disc-like. After $z \sim 1$ the AGN simulations result in lower mass, older, less metal rich and slower rotating systems with less disky isophotes - in general agreement with observations. Two-dimensional kinematic maps of in-situ and accreted stars show that these differences result from reduced in-situ star formation due to AGN feedback. A full analysis of stellar orbits indicates that galaxies simulated with AGN are typically more triaxial and have higher fractions of x-tubes and box orbits and lower fractions of z-tubes. This trend can also be explained by reduced late in-situ star formation. We introduce a global parameter, $\xi_3$ , to characterise the anti-correlation between the third-order kinematic moment $h_3$ and the line-of-sight velocity ($v_{los}/{\sigma}$), and compare to ATLAS$^{3D}$ observations. The kinematic asymmetry parameter $\xi_3$ might be a useful diagnostic for large integral field surveys as it is a kinematic indicator for intrinsic shape and orbital content

On the Effects of Local Environment on Active Galactic Nucleus (AGN) in the Horizon Run 5 Simulation

We use the Horizon Run 5 cosmological simulation to study the effect of galaxy intrinsic properties and the local environment on active galactic nuclei (AGNs) characterized by their threshold of the accretion rate. We select galaxies in the stellar mass range 10 9.5 ≤ M * / M ⊙ ≤ 10 10.5 in the snapshot at redshift z = 0.625. Among various intrinsic properties, we find that the star formation rate of the host galaxy is most correlated to the AGN activity. To quantify the environment, we use background galaxy number density (large-scale environment) and distance and morphological type of the nearest neighbors (small-scale environment), and study their relative effects on the AGN properties. We find that, compared to the background density, the nearest neighbor environment is the dominant quantity determining the bolometric luminosity, star formation rate, and kinematic properties of AGNs and better dictates the gas mass of the host galaxy. We show that the cold gas content in the host galaxies is crucial in triggering AGN activity. However, when the nearest neighbor environment effects start to act at the neighbor distance of less than about half the virial radius of the neighbor, the neighbor environmental effects are the most dominant factor for quasar activity