ALBERT

Description: The SILCC (SImulating the Life-Cycle of molecular Clouds) project aims to self-consistently understand the small-scale structure of the interstellar medium (ISM) and its link to galaxy evolution. We simulate the evolution of the multiphase ISM in a (500 pc) 2   x  ±5 kpc region of a galactic disc, with a gas surface density of $\Sigma _{_{\rm GAS}} = 10 \;{\rm M}_{\odot }\,{\rm pc}^{-2}$ . The flash 4 simulations include an external potential, self-gravity, magnetic fields, heating and radiative cooling, time-dependent chemistry of H 2 and CO considering (self-) shielding, and supernova (SN) feedback but omit shear due to galactic rotation. We explore SN explosions at different rates in high-density regions ( peak ), in random locations with a Gaussian distribution in the vertical direction ( random ), in a combination of both ( mixed ), or clustered in space and time ( clus / clus2 ). Only models with self-gravity and a significant fraction of SNe that explode in low-density gas are in agreement with observations. Without self-gravity and in models with peak driving the formation of H 2 is strongly suppressed. For decreasing SN rates, the H 2 mass fraction increases significantly from 〈10 per cent for high SN rates, i.e. 0.5 dex above Kennicutt–Schmidt, to 70–85 per cent for low SN rates, i.e. 0.5 dex below KS. For an intermediate SN rate, clustered driving results in slightly more H 2 than random driving due to the more coherent compression of the gas in larger bubbles. Magnetic fields have little impact on the final disc structure but affect the dense gas ( n   10 cm –3 ) and delay H 2 formation. Most of the volume is filled with hot gas (~80 per cent within ±150 pc). For all but peak driving a vertically expanding warm component of atomic hydrogen indicates a fountain flow. We highlight that individual chemical species populate different ISM phases and cannot be accurately modelled with temperature-/density-based phase cut-offs.

Description: We present the results of a high-resolution, 5 GHz, Karl G. Jansky Very Large Array study of the nuclear radio emission in a representative subset of the atlas 3D survey of early-type galaxies (ETGs). We find that 51 ± 4 per cent of the ETGs in our sample contain nuclear radio emission with luminosities as low as 10 18 W Hz –1 . Most of the nuclear radio sources have compact (25–110 pc) morphologies, although ~10 per cent display multicomponent core+jet or extended jet/lobe structures. Based on the radio continuum properties, as well as optical emission line diagnostics and the nuclear X-ray properties, we conclude that the majority of the central 5 GHz sources detected in the atlas 3D galaxies are associated with the presence of an active galactic nucleus (AGN). However, even at subarcsecond spatial resolution, the nuclear radio emission in some cases appears to arise from low-level nuclear star formation rather than an AGN, particularly when molecular gas and a young central stellar population is present. This is in contrast to popular assumptions in the literature that the presence of a compact, unresolved, nuclear radio continuum source universally signifies the presence of an AGN. Additionally, we examine the relationships between the 5 GHz luminosity and various galaxy properties including the molecular gas mass and – for the first time – the global kinematic state. We discuss implications for the growth, triggering, and fuelling of radio AGNs, as well as AGN-driven feedback in the continued evolution of nearby ETGs.

Description: We investigate the early impact of single and binary supernova (SN) explosions on dense gas clouds with three-dimensional, high-resolution, hydrodynamic simulations. The effect of cloud structure, radiative cooling and ionizing radiation from the progenitor stars on the net input of kinetic energy, f kin  =  E kin / E SN , thermal energy, f therm  =  E therm / E SN , and gas momentum, f P  =  P / P SN , to the interstellar medium (ISM) is tested. For clouds with $\bar{n} = 100\;{\rm cm}^{-3}$ , the momentum generating Sedov and pressure-driven snowplough phases are terminated early (0.01 Myr) and radiative cooling limits the coupling to f therm  ~ 0.01, f kin  ~ 0.05, and f P  ~ 9, significantly lower than for the case without cooling. For pre-ionized clouds, these numbers are only increased by ~50 per cent, independent of the cloud structure. This only suffices to accelerate ~5 per cent of the cloud to radial velocities 30 km s –1 . A second SN might enhance the coupling efficiencies if delayed past the Sedov phase of the first explosion. Such very low coupling efficiencies cast doubts on many subresolution models for SN feedback, which are, in general, validated a posteriori. Ionizing radiation appears not to significantly enhance the coupling of SNe to the surrounding gas as it drives the ISM into inert dense shells and cold clumps, a process which is unresolved in galaxy-scale simulations. Our results indicate that the momentum input of SNe in ionized, structured clouds is larger (more than a factor of 10) than the corresponding momentum yield of the progenitor's stellar winds.

Description: Supernova (SN) blast waves inject energy and momentum into the interstellar medium (ISM), control its turbulent multiphase structure and the launching of galactic outflows. Accurate modelling of the blast wave evolution is therefore essential for ISM and galaxy formation simulations. We present an efficient method to compute the input of momentum, thermal energy, and the velocity distribution of the shock-accelerated gas for ambient media (densities of 0.1 ≥ n 0 [cm – 3 ] ≥ 100) with uniform (and with stellar wind blown bubbles), power-law, and turbulent (Mach numbers $\mathcal {M}$ from 1to100) density distributions. Assuming solar metallicity cooling, the blast wave evolution is followed to the beginning of the momentum conserving snowplough phase. The model recovers previous results for uniform ambient media. The momentum injection in wind-blown bubbles depend on the swept-up mass and the efficiency of cooling, when the blast wave hits the wind shell. For power-law density distributions with n ( r ) ~  r –2 (for n ( r ) 〉  n floor ) the amount of momentum injection is solely regulated by the background density n floor and compares to n uni = n floor . However, in turbulent ambient media with lognormal density distributions the momentum input can increase by a factor of 2 (compared to the homogeneous case) for high Mach numbers. The average momentum boost can be approximated as $p_{{\rm turb}}/{p_{{0}}}\ =23.07\, \left(\frac{n_{{0,\rm turb}}}{1\,{\rm cm}^{-3}}\right)^{-0.12} + 0.82 (\ln (1+b^{2}\mathcal {M}^{2}))^{1.49}\left(\frac{n_{{0,\rm turb}}}{1\,{\rm cm}^{-3}}\right)^{-1.6}$ . The velocity distributions are broad as gas can be accelerated to high velocities in low-density channels. The model values agree with results from recent, computationally expensive, three-dimensional simulations of SN explosions in turbulent media.

Description: We observed the lenticular galaxy NGC 3998 with the Mitchell Integral-Field Spectrograph and extracted line-of-sight velocity distributions out to three half-light radii. We constructed collisionless orbit models in order to constrain NGC 3998's dark and visible structure, using kinematics from both the Mitchell and SAURON instruments. We find NGC 3998 to be almost axisymmetric, seen nearly face-on with a flattened intrinsic shape – i.e. a face-on fast rotator. We find an I -band mass-to-light ratio of $4.7_{-0.45}^{+0.32}$ in good agreement with previous spectral fitting results for this galaxy. Our best-fitting orbit model shows a both a bulge and a disc component, with a non-negligible counter-rotating component also evident. We find that relatively little dark matter is needed to model this galaxy, with an inferred dark mass fraction of just $(7.1^{+8.1}_{-7.1}){\rm per cent}$ within one half-light radius.

Description: We compare the performance of mass estimators for elliptical galaxies that rely on the directly observable surface brightness and velocity dispersion profiles, without invoking computationally expensive detailed modelling. These methods recover the mass at a specific radius where the mass estimate is expected to be least sensitive to the anisotropy of stellar orbits. One uses the total luminosity-weighted velocity dispersion and evaluates the mass at a 3D half-light radius r 1/2 , i.e. it depends on the global galaxy properties. Another approach estimates the mass from the velocity dispersion at a radius R 2 where the surface brightness declines as R –2 , i.e. it depends on the local properties. We evaluate the accuracy of the two methods for analytical models, simulated galaxies and real elliptical galaxies that have already been modelled by the Schwarzschild's orbit-superposition technique. Both estimators recover an almost unbiased circular speed estimate with a modest rms scatter (10 per cent). Tests on analytical models and simulated galaxies indicate that the local estimator has a smaller rms scatter than the global one. We show by examination of simulated galaxies that the projected velocity dispersion at R 2 could serve as a good proxy for the virial galaxy mass. For simulated galaxies the total halo mass scales with p ( R 2 ) as $ M_{\rm vir} [\mathrm{M}_{{\odot }}\,h^{-1}] \approx 6\times 10^{12}({{\sigma _{\rm p}(R_2)}\over{200\, \rm km\, s^{-1}}})^{4}$ with rms scatter 40 per cent.

Description: Accurate direct N -body simulations help to obtain detailed information about the dynamical evolution of star clusters. They also enable comparisons with analytical models and Fokker-Planck or Monte Carlo methods. nbody6 is a well-known direct N -body code for star clusters, and nbody6++ is the extended version designed for large particle number simulations by supercomputers. We present nbody6++gpu , an optimized version of nbody6++ with hybrid parallelization methods (MPI, GPU, OpenMP, and AVX/SSE) to accelerate large direct N -body simulations, and in particular to solve the million-body problem. We discuss the new features of the nbody6++gpu code, benchmarks, as well as the first results from a simulation of a realistic globular cluster initially containing a million particles. For million-body simulations, nbody6++gpu is 400–2000 times faster than nbody6 with 320 CPU cores and 32 NVIDIA K20X GPUs. With this computing cluster specification, the simulations of million-body globular clusters including 5 per cent primordial binaries require about an hour per half-mass crossing time.

Description: We employ cosmological hydrodynamical simulations to investigate the effects of AGN feedback on the formation of massive galaxies with present-day stellar masses of $M_{\rm stel}= 8.8 \times 10^{10}{\rm -}6.0 \times 10^{11} {\thinspace {\rm M}_{{\odot }}}$ . 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 haloes 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 haloes and trace their mass growth via gas accretion and mergers with other black holes. Both feedback models successfully recover the observed M BH – relation and black hole-to-stellar mass ratio for simulated central early-type galaxies. The baryonic conversion efficiencies are reduced by a factor of 2 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  = 200 km s – 1 , the X-ray luminosity is reduced from 10 42 erg s – 1 to 10 40 erg s – 1 . 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.

Description: The SILCC (SImulating the Life-Cycle of molecular Clouds) project aims to self-consistently understand the small-scale structure of the interstellar medium (ISM) and its link to galaxy evolution. We simulate the evolution of the multiphase ISM in a (500 pc) 2   x  ±5 kpc region of a galactic disc, with a gas surface density of $\Sigma _{_{\rm GAS}} = 10 \;{\rm M}_{\odot }\,{\rm pc}^{-2}$ . The flash 4 simulations include an external potential, self-gravity, magnetic fields, heating and radiative cooling, time-dependent chemistry of H 2 and CO considering (self-) shielding, and supernova (SN) feedback but omit shear due to galactic rotation. We explore SN explosions at different rates in high-density regions ( peak ), in random locations with a Gaussian distribution in the vertical direction ( random ), in a combination of both ( mixed ), or clustered in space and time ( clus / clus2 ). Only models with self-gravity and a significant fraction of SNe that explode in low-density gas are in agreement with observations. Without self-gravity and in models with peak driving the formation of H 2 is strongly suppressed. For decreasing SN rates, the H 2 mass fraction increases significantly from 〈10 per cent for high SN rates, i.e. 0.5 dex above Kennicutt–Schmidt, to 70–85 per cent for low SN rates, i.e. 0.5 dex below KS. For an intermediate SN rate, clustered driving results in slightly more H 2 than random driving due to the more coherent compression of the gas in larger bubbles. Magnetic fields have little impact on the final disc structure but affect the dense gas ( n   10 cm –3 ) and delay H 2 formation. Most of the volume is filled with hot gas (~80 per cent within ±150 pc). For all but peak driving a vertically expanding warm component of atomic hydrogen indicates a fountain flow. We highlight that individual chemical species populate different ISM phases and cannot be accurately modelled with temperature-/density-based phase cut-offs.

Description: The SILCC project (SImulating the Life-Cycle of molecular Clouds) aims at a more self-consistent understanding of the interstellar medium (ISM) on small scales and its link to galaxy evolution. We present three-dimensional (magneto)hydrodynamic simulations of the ISM in a vertically stratified box including self-gravity, an external potential due to the stellar component of the galactic disc, and stellar feedback in the form of an interstellar radiation field and supernovae (SNe). The cooling of the gas is based on a chemical network that follows the abundances of H + , H, H 2 , C + , and CO and takes shielding into account consistently. We vary the SN feedback by comparing different SN rates, clustering and different positioning, in particular SNe in density peaks and at random positions, which has a major impact on the dynamics. Only for random SN positions the energy is injected in sufficiently low-density environments to reduce energy losses and enhance the effective kinetic coupling of the SNe with the gas. This leads to more realistic velocity dispersions ( $\sigma _\mathrm{H\,{\small {I}}}\approx 0.8\sigma _{300\rm{-}8000\,\mathrm{K}}\sim 10\hbox{-}20\,\mathrm{km}\,\mathrm{s}^{-1}$ , $\sigma _\mathrm{H\,\alpha }\approx 0.6\sigma _{8000-3\times 10^5\,\mathrm{K}}\sim 20\hbox{-}30\,\mathrm{km}\,\mathrm{s}^{-1}$ ), and strong outflows with mass loading factors (ratio of outflow to star formation rate) of up to 10 even for solar neighbourhood conditions. Clustered SNe abet the onset of outflows compared to individual SNe but do not influence the net outflow rate. The outflows do not contain any molecular gas and are mainly composed of atomic hydrogen. The bulk of the outflowing mass is dense ( ~ 10 –25 –10 –24 g cm –3 ) and slow ( v ~ 20–40 km s –1 ) but there is a high-velocity tail of up to v ~ 500 km s –1 with ~ 10 –28 –10 –27 g cm –3 .