Using angular momentum maps to detect kinematically distinct galactic components

In this work, we introduce a physically motivated method of performing disc/spheroid decomposition of simulated galaxies, which we apply to the EAGLE sample. We make use of the HEALPIX package to create Mollweide projections of the angular momentum map of each galaxy’s stellar particles. A number of features arise on the angular momentum space which allows us to decompose galaxies and classify them into different morphological types. We assign stellar particles with angular separation of less/greater than 30° from the densest grid cell on the angular momentum sphere to the disc/spheroid components, respectively. We analyse the spatial distribution for a subsample of galaxies and show that the surface density profiles of the disc and spheroid closely follow an exponential and a Sérsic profile, respectively. In addition discs rotate faster, have smaller velocity dispersions, are younger and are more metal rich than spheroids. Thus, our morphological classification reproduces the observed properties of such systems. Finally, we demonstrate that our method is able to identify a significant population of galaxies with counter-rotating discs and provide a more realistic classification of such systems compared to previous methods

Morphological evolution and galactic sizes in the L-Galaxies SA model

In this work we update theL-Galaxiessemi-analytic model (SAM) to better follow thephysical processes responsible for the growth of bulges via disc instabilities (leading to pseudo-bulges) and mergers (leading to classical bulges). We address the former by considering thecontribution of both stellar and gaseous discs in the stability of the galaxy, and we update thelatter by including dissipation of energy in gas-rich mergers. Furthermore, we introduce angularmomentum losses during cooling and find that an accurate match to the observed correlationbetween stellar disc scale length and mass atz∼0.0requires that the gas loses 20%of its initialspecific angular momentum to the corresponding dark matter halo during the formation of thecold gas disc. We reproduce the observed trends between the stellar mass and specific angularmomentum for both disc- and bulge-dominated galaxies, with the former rotating faster thanthe latter of the same mass. We conclude that a two-component instability recipe provides amorphologically diverse galaxy sample which matches the observed fractional breakdown ofgalaxies into different morphological types. This recipe also enables us to obtain an excellent fitto the morphology-mass relation and stellar mass function of different galactic types. Finally, we find that energy dissipation during mergers reduces the merger remnant sizes and allowsus to match the observed mass-size relation for bulge-dominated system

The complex evolution of supermassive black holes in cosmological simulations

We present here self-consistent zoom-in simulations of massive galaxies forming in a full cosmological setting. The simulations are run with an updated version of the KETJU code, which is able to resolve the gravitational dynamics of their supermassive black holes, while simultaneously modelling the large-scale astrophysical processes in the surrounding galaxies, such as gas cooling, star formation and stellar and AGN feedback. The KETJU code is able to accurately model the complex behaviour of multiple SMBHs, including dynamical friction, stellar scattering and gravitational wave emission, and also to resolve Lidov–Kozai oscillations that naturally occur in hierarchical triplet SMBH systems. In general most of the SMBH binaries form at moderately high eccentricities, with typical values in the range of , meaning that the circular binary models that are commonly used in the literature are insufficient for capturing the typical binary evolution.Non peer reviewe

The challenge of simulating the star cluster population of dwarf galaxies with resolved interstellar medium

We present results on the star cluster properties from a series of high resolution smoothed particles hydrodynamics (SPH) simulations of isolated dwarf galaxies as part of the GRIFFIN project. The simulations at sub-parsec spatial resolution and a minimum particle mass of 4 M-circle dot incorporate non-equilibrium heating, cooling, and chemistry processes, and realize individual massive stars. The simulations follow feedback channels of massive stars that include the interstellar-radiation field variable in space and time, the radiation input by photo-ionization and supernova explosions. Varying the star formation efficiency per free-fall time in the range epsilon(ff) = 0.2-50 per cent neither changes the star formation rates nor the outflow rates. While the environmental densities at star formation change significantly with epsilon(ff), the ambient densities of supernovae are independent of epsilon(ff) indicating a decoupling of the two processes. At low epsilon(ff), gas is allowed to collapse more before star formation, resulting in more massive, and increasingly more bound star clusters are formed, which are typically not destroyed. With increasing epsilon(ff), there is a trend for shallower cluster mass functions and the cluster formation efficiency Gamma for young bound clusters decreases from 50 per cent to similar to 1 per cent showing evidence for cluster disruption. However, none of our simulations form low mass (Peer reviewe

KETJU -- resolving small-scale supermassive black hole dynamics in GADGET-4

We present the new public version of the KETJU supermassive black hole (SMBH) dynamics module, as implemented into GADGET-4. KETJU adds a small region around each SMBH where the dynamics of the SMBHs and stellar particles are integrated using an algorithmically regularised integrator instead of the leapfrog integrator with gravitational softening used by GADGET-4. This enables modelling SMBHs as point particles even during close interactions with stellar particles or other SMBHs, effectively removing the spatial resolution limitation caused by gravitational softening. KETJU also includes post-Newtonian corrections, which allows following the dynamics of SMBH binaries to sub-parsec scales and down to tens of Schwarzschild radii. Systems with multiple SMBHs are also supported, with the code also including the leading non-linear cross terms that appear in the post-Newtonian equations for such systems. We present tests of the code showing that it correctly captures, at sufficient mass resolution, the sinking driven by dynamical friction and binary hardening driven by stellar scattering. We also present an example application demonstrating how the code can be applied to study the dynamics of SMBHs in mergers of multiple galaxies and the effect they have on the properties of the surrounding galaxy. We expect that the presented KETJU SMBH dynamics module can also be straightforwardly incorporated into other codes similar to GADGET-4, which would allow coupling small-scale SMBH dynamics to the rich variety of galactic physics models that exist in the literature.Comment: 21 pages, 19 figures. Code available from https://www.mv.helsinki.fi/home/phjohans/ketj

Modelling the accretion and feedback of supermassive black hole binaries in gas-rich galaxy mergers

Peer reviewe

First Light and Reionisation Epoch Simulations (FLARES) X: Environmental Galaxy Bias and Survey Variance at High Redshift

Upcoming deep galaxy surveys with JWST will probe galaxy evolution during the epoch of reionisation (EoR, $5\leq z\leq10$) over relatively compact areas (e.g. $\sim$ 300\,arcmin$^2$ for the JADES GTO survey). It is therefore imperative that we understand the degree of survey variance, to evaluate how representative the galaxy populations in these studies will be. We use the First Light And Reionisation Epoch Simulations (FLARES) to measure the galaxy bias of various tracers over an unprecedentedly large range in overdensity for a hydrodynamic simulation, and use these relations to assess the impact of bias and clustering on survey variance in the EoR. Star formation is highly biased relative to the underlying dark matter distribution, with the mean ratio of the stellar to dark matter density varying by a factor of 100 between regions of low and high matter overdensity (smoothed on a scale of 14\,$h^{-1}$cMpc). This is reflected in the galaxy distribution -- the most massive galaxies are found solely in regions of high overdensity. As a consequence of the above, galaxies in the EoR are highly clustered, which can lead to large variance in survey number counts. For mean number counts $N\lesssim 100$ (1000), in a unit redshift slice of angular area 300\,arcmin$^2$ (1.4\,deg$^2$), the 2-sigma range in $N$ is roughly a factor of four (two). We present relations between the expected variance and survey area for different survey geometries; these relations will be of use to observers wishing to understand the impact of survey variance on their results.Comment: 14 pages, 17 figures. Paper 10 in the First Light and Reionisation Epoch Simulations (FLARES) serie

First Light And Reionisation Epoch Simulations (FLARES) : IV. The size evolution of galaxies at z ≥ 5

We present the intrinsic and observed sizes of galaxies at z >= 5 in the First Light And Reionisation Epoch Simulations (flares). We employ the large effective volume of flares to produce a sizeable sample of high-redshift galaxies with intrinsic and observed luminosities and half-light radii in a range of rest-frame ultraviolet (UV) and visual photometric bands. This sample contains a significant number of intrinsically ultracompact galaxies in the far-UV (1500 angstrom), leading to a negative intrinsic far-UV size-luminosity relation. However, after the inclusion of the effects of dust these same compact galaxies exhibit observed sizes that are as much as 50 times larger than those measured from the intrinsic emission, and broadly agree with a range of observational samples. This increase in size is driven by the concentration of dust in the core of galaxies, heavily attenuating the intrinsically brightest regions. At fixed luminosity we find a galaxy size redshift evolution with a slope of m = 1.21-1.87 depending on the luminosity sample in question, and we demonstrate the wavelength dependence of the size-luminosity relation that will soon be probed by the James Webb Space Telescope.Peer reviewe

First Light and Reionisation Epoch Simulations (FLARES) - VI. The colour evolution of galaxies z=5-15

With its exquisite sensitivity, wavelength coverage, and spatial and spectral resolution, the James Webb Space Telescope (JWST) is poised to revolutionize our view of the distant, high-redshift (z > 5) Universe. While Webb's spectroscopic observations will be transformative for the field, photometric observations play a key role in identifying distant objects and providing more comprehensive samples than accessible to spectroscopy alone. In addition to identifying objects, photometric observations can also be used to infer physical properties and thus be used to constrain galaxy formation models. However, inferred physical properties from broad-band photometric observations, particularly in the absence of spectroscopic redshifts, often have large uncertainties. With the development of new tools for forward modelling simulations, it is now routinely possible to predict observational quantities, enabling a direct comparison with observations. With this in mind, in this work, we make predictions for the colour evolution of galaxies at z = 5-15 using the First Light And Reionisation Epoch Simulations (flares) cosmological hydrodynamical simulation suite. We predict a complex evolution with time, driven predominantly by strong nebular line emission passing through individual bands. These predictions are in good agreement with existing constraints from Hubble and Spitzer as well as some of the first results from Webb. We also contrast our predictions with other models in the literature: While the general trends are similar, we find key differences, particularly in the strength of features associated with strong nebular line emission. This suggests photometric observations alone should provide useful discriminating power between different models and physical states of galaxies.Peer reviewe