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Register a new userFirst Light And Reionisation Epoch Simulations (FLARES) I: Environmental Dependence of High-Redshift Galaxy Evolution
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We introduce the First Light And Reionisation Epoch Simulations (FLARES), a suite of zoom simulations using the EAGLE model. We resimulate a range of overdensities during the Epoch of Reionisation (EoR) in order to build composite distribution functions, as well as explore the environmental dependence of galaxy formation and evolution during this critical period of galaxy assembly. The regions are selected from a large $(3.2 ;mathrm{cGpc})^{3}$ parent volume, based on their overdensity within a sphere of radius $14,h^{-1};mathrm{cMpc}$. We then resimulate with full hydrodynamics, and employ a novel weighting scheme that allows the construction of composite distribution functions that are representative of the full parent volume. This significantly extends the dynamic range compared to smaller volume periodic simulations. We present an analysis of the galaxy stellar mass function (GSMF), the star formation rate distribution function (SFRF) and the star forming sequence (SFS) predicted by flares, and compare to a number of observational and model constraints. We also analyse the environmental dependence over an unprecedented range of overdensity. Both the GSMF and the SFRF exhibit a clear double-Schechter form, up to the highest redshifts ($z = 10$). We also find no environmental dependence of the SFS normalisation. The increased dynamic range probed by FLARES will allow us to make predictions for a number of large area surveys that will probe the EoR in coming years, such as WFIRST and Euclid.
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We present the photometric properties of galaxies in the First Light and Reionisation Epoch Simulations (FLARES). The simulations trace the evolution of galaxies in a range of overdensities through the Epoch of Reionistion (EoR). With a novel weighting scheme we combine these overdensities, extending significantly the dynamic range of observed composite distribution functions compared to periodic simulation boxes. FLARES predicts a significantly larger number of intrinsically bright galaxies, which can be explained through a simple model linking dust-attenuation to the metal content of the interstellar medium, using a line-of-sight (LOS) extinction model. With this model we present the photometric properties of the FLARES galaxies for $z in [5,10]$. We show that the ultraviolet (UV) luminosity function (LF) matches the observations at all redshifts. The function is fit by Schechter and double power-law forms, with the latter being favoured at these redshifts by the FLARES composite UV LF. We also present predictions for the UV continuum slope as well as the attenuation in the UV. The impact of environment on the UV LF is also explored, with the brightest galaxies forming in the densest environments. We then present the line luminosity and equivalent widths of some prominent nebular emission lines arising from the galaxies, finding rough agreement with available observations. We also look at the relative contribution of obscured and unobscured star formation, finding comparable contributions at these redshifts.
Using the First Light And Reionisation Epoch Simulations (textsc{Flares}) we explore the dust driven properties of massive high-redshift galaxies at $zin[5,10]$. By post-processing the galaxy sample using the radiative transfer code textsc{skirt} we obtain the full spectral energy distribution. We explore the resultant luminosity functions, IRX-$beta$ relations as well as the luminosity-weighted dust temperatures in the Epoch of Reionisation (EoR). We find that most of our results are in agreement with the current set of observations, but under-predict the number densities of bright IR galaxies, which are extremely biased towards the most overdense regions. We see that the textsc{Flares} IRX-$beta$ relation (for $5le zle8$) predominantly follows the local starburst relation. The IRX shows an increase with stellar mass, plateauing at the high-mass end ($sim10^{10}$M$_{odot}$) and shows no evolution in the median normalisation with redshift. We also look at the dependence of the peak dust temperature (T$_{mathrm{peak}}$) on various galaxy properties including the stellar mass, IR luminosity and sSFR, finding the correlation to be strongest with sSFR. The luminosity-weighted dust temperatures increase towards higher redshifts, with the slope of the T$_{mathrm{peak}}$ - redshift relation showing a higher slope than the lower redshift relations obtained from previous observational and theoretical works. The results from textsc{Flares}, which is able to provide a better statistical sample of high-redshift galaxies compared to other simulations, provides a distinct vantage point for the high-redshift Universe.
[abridged] This work aims to observationally investigate the history of size growth of early-type galaxies and how the growth depends on cosmic epoch and the mass of the halo in which they are embedded. We carried out a photometric and structural analysis in the rest-frame $V$ band of a mass-selected ($log M/M_odot >10.7$) sample of red-sequence early-type galaxies with spectroscopic/grism redshift in the general field up to $z=2$ to complement a previous work presenting an identical analysis but in halos 100 times more massive and 1000 times denser. We homogeneously derived sizes (effective radii) fully accounting for the multi-component nature of galaxies and the common presence of isophote twists and ellipticity gradients. By using these mass-selected samples, composed of 170 red-sequence early-type galaxies in the general field and 224 identically selected and analyzed in clusters, we isolate the effect on galaxy sizes of the halo in which galaxies are embedded and its dependence on epoch. We find that the $log$ of the galaxy size at a fixed stellar mass, $log M/M_odot= 11$, has increased with epoch at a rate twice as fast in the field than in cluster in the last 10 Gyr ($0.26pm0.03$ versus $0.13pm0.02$ dex per unit redshift). Red-sequence early-type galaxies in the general field reached the size of their cousins in denser environment by $z=0.25pm0.13$ in spite of being three times smaller at $zsim2$. Data point toward a model where size growth is epoch-independent (i.e., $partial log r_e /partial z = c$), but with a rate $c$ depending on environment, $partial c /partial log M_{halo} approx 0.05$. Environment determines the growth rate ($d log r_e / dz$) at all redshifts, indicating an external origin for the galaxy growth without any clear epoch where it ceases to have an effect.
We study the evolution of the Red Sequence (RS) scatter in galaxy clusters and groups simultaneously using predictions from our simulations (cosmological hydrodynamic + semi-analytical) as well as observational data from the HAWK-I Cluster Survey (HCS), a sample of galaxy clusters at redshifts $0.8 < z < 1.5$. We analyze the intrinsic scatter of the RS to investigate whether the stellar age can be its main effective driver, at the same time assessing the role of metallicity variations in shaping the RS building at around epoch $zsim$1 and beyond. To this purpose we rely on various methods to derive the average age and age spread from the RS colour scatter of the HCS sample, with the aid of population synthesis models. The RS scatter predicted by the models at $z< 0.7$ is found to not depend on the star formation history adopted, whilst at $z>the correlation found between age and rest-frame colour scatters is quite robust, although all age scatter estimations ultimately depend on the definition of RS as well as on the completeness limits adopted. We find that the age spread of RS galaxies predicted by both hydrodynamical simulations and SAM increases with cosmic epoch, while the ratio between the age spread and the average age remains approximately constant. Both trends are in agreement with observational results from both the HCS and other literature samples.
The existence of a kinematic morphology-density relation remains uncertain, and instead stellar mass appears the more dominant driver of galaxy kinematics. We investigate the dependence of the stellar spin parameter proxy $lambda_{R_e}$ on environment using a marked cross-correlation method with data from the SAMI Galaxy Survey. Our sample contains 710 galaxies with spatially resolved stellar velocity and velocity dispersion measurements. By utilising the highly complete spectroscopic data from the GAMA survey, we calculate marked cross-correlation functions for SAMI galaxies using a pair count estimator and marks based on stellar mass and $lambda_{R_e}$. We detect an anti-correlation of stellar kinematics with environment at the 3.2$sigma$ level, such that galaxies with low $lambda_{R_e}$ values are preferably located in denser galaxy environments. However, a significant correlation between stellar mass and environment is also found (correlation at 2.4$sigma$), as found in previous works. We compare these results to mock-observations from the cosmological EAGLE simulations, where we find a similar significant $lambda_{R_e}$ anti-correlation with environment, and a mass and environment correlation. We demonstrate that the environmental correlation of $lambda_{R_e}$ is not caused by the mass-environment relation. The significant relationship between $lambda_{R_e}$ and environment remains when we exclude slow rotators. The signals in SAMI and EAGLE are strongest on small scales (10-100 kpc) as expected from galaxy interactions and mergers. Our work demonstrates that the technique of marked correlation functions is an effective tool for detecting the relationship between $lambda_{R_e}$ and environment.
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