Given its velocity dispersion, the early-type galaxy NGC 1600 has an unusually massive (M • = 1.7 × 10 10 M ) central supermassive black hole (SMBH), surrounded by a large core (r b = 0.7 kpc) with a tangentially biased stellar distribution. We present high-resolution equal-mass merger simulations including SMBHs to study the formation of such systems. The structural parameters of the progenitor ellipticals were chosen to produce merger remnants resembling NGC 1600. We test initial stellar density slopes of ρ ∝ r −1 and ρ ∝ r −3/2 and vary the initial SMBH masses from 8.5 × 10 8 to 8.5 × 10 9 M . With increasing SMBH mass the merger remnants show a systematic decrease in central surface brightness, an increasing core size, and an increasingly tangentially biased central velocity anisotropy. Two-dimensional kinematic maps reveal decoupled, rotating core regions for the most massive SMBHs. The stellar cores form rapidly as the SMBHs become bound, while the velocity anisotropy develops more slowly after the SMBH binaries become hard. The simulated merger remnants follow distinct relations between the core radius and the sphere-of-influence, and the SMBH mass, similar to observed systems. We find a systematic change in the relations as a function of the progenitor density slope, and present a simple scouring model reproducing this behavior. Finally, we find the best agreement with NGC 1600 using SMBH masses totaling the observed value of M • = 1.7 × 10 10 M . In general, density slopes of ρ ∝ r −3/2 for the progenitor galaxies are strongly favored for the equal-mass merger scenario.

We study the impact of merging supermassive black holes (SMBHs) on the central regions of massive early-type galaxies (ETGs) using a series of merger simulations with varying mass ratios. The ETG models include realistic stellar and dark matter components and are evolved with the gadget-3 based regularized tree code ketju. We show that observed key properties of the nuclear stellar populations of massive ETGs, namely flat stellar density distributions (cores), tangentially biased velocity distributions and kinematically decoupled (counter-)rotation can naturally result from a single process − the scouring by SMBHs. Major mergers with mass ratios of q > 1/3 produce flat, tangentially biased cores with kinematically distinct components. These kinematic features originate from reversals of the SMBH orbits caused by gravitational torques after pericenter passages. Minor mergers (q 1/3) on the other hand, form non-rotating cores and the orbit reversal becomes less important. Low-density stellar cores scoured in (multiple) minor mergers are less tangentially biased. This implies that the nuclear stellar properties of massive ETGs can be solely explained by stellar dynamical processes during their final assembly without any need for 'feedback' from accreting black holes. We predict a strong correlation between decoupled cores, central anisotropy and merger history: decoupled cores form in binary mergers and we predict them to occur in elliptical galaxies with the strongest central anisotropy. Measurements of the central orbital structure are the key to understanding the number of mergers a given galaxy has experienced.

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 ∼ 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, ξ 3 , to characterise the anti-correlation between the third-order kinematic moment h 3 and the line-of-sight velocity (v los /σ), and compare to ATLAS 3D observations. The kinematic asymmetry parameter ξ 3 might be a useful diagnostic for large integral field surveys as it is a kinematic indicator for intrinsic shape and orbital content.

We present SMART, a new 3D implementation of the Schwarzschild Method and its application to a triaxial N-body merger simulation. SMART fits full line-of-sight velocity distributions (LOSVDs) to determine the viewing angles, black hole, stellar and dark matter (DM) masses and the stellar orbit distribution of galaxies. Our model uses a 5D orbital starting space to ensure a representative set of stellar trajectories adaptable to the integrals-of-motion space and it is designed to deal with non-parametric stellar and DM densities. SMART’s efficiency is demonstrated by application to a realistic N-body merger simulation including supermassive black holes which we model from five different projections. When providing the true viewing angles, 3D stellar luminosity profile and normalized DM halo, we can (i) reproduce the intrinsic velocity moments and anisotropy profile with a precision of $\sim 1\%$ and (ii) recover the black hole mass, stellar mass-to-light ratio and DM normalization to better than a few percent accuracy. This precision is smaller than the currently discussed differences between initial-stellar-mass functions and scatter in black hole scaling relations. Further tests with toy models suggest that the recovery of the anisotropy in triaxial galaxies is almost unique when the potential is known and full LOSVDs are fitted. We show that orbit models even allow the reconstruction of full intrinsic velocity distributions, which contain more information than the classical anisotropy parameter. Surprisingly, the orbit library for the analysed N-body simulation’s gravitational potential contains orbits with net rotation around the intermediate axis that is stable over some Gyrs.

We present a high-resolution smoothed particle hydrodynamics simulation of the Antennae galaxies (NGC 4038/4039) and follow the evolution 3 Gyrs beyond the final coalescence. The simulation includes metallicity dependent cooling, star formation, and both stellar feedback and chemical enrichment. The simulated best-match Antennae reproduces well both the observed morphology and the off-nuclear starburst. We also produce for the first time a simulated two-dimensional metallicity map of the Antennae and find good agreement with the observed metallicity of off-nuclear stellar clusters, however the nuclear metallicities are overproduced by ∼ 0.5 dex. Using the radiative transfer code SKIRT we produce multi-wavelength observations of both the Antennae and the merger remnant. The 1 Gyr old remnant is well fitted with a Sérsic profile of n = 7.07, and with an r-band effective radius of r e = 1.6 kpc and velocity dispersion of σ e = 180 km/s the remnant is located on the fundamental plane of early-type galaxies (ETGs). The initially blue Antennae remnant evolves onto the red sequence after ∼ 2.5 Gyr of secular evolution. The remnant would be classified as a fast rotator, as the specific angular momentum evolves from λ Re ≈ 0.11 to λ Re ≈ 0.14 during its evolution. The remnant shows ordered rotation and a double peaked maximum in the mean 2D line-of-sight velocity. These kinematical features are relatively common among local ETGs and we specifically identify three local ETGs (NGC 3226, NGC 3379 and NGC 4494) in the ATLAS 3D sample, whose photometric and kinematic properties most resemble the Antennae remnant.