The Local Group galaxies offer some of the most discriminating tests of models of cosmic structure formation. For example, observations of the Milky Way (MW) and Andromeda satellite populations ...appear to be in disagreement with N-body simulations of the ‘lambda cold dark matter’ (ΛCDM) model: there are far fewer satellite galaxies than substructures in CDM haloes (the ‘missing satellites’ problem); dwarf galaxies seem to avoid the most massive substructures (the ‘too-big-to-fail’ problem); and the brightest satellites appear to orbit their host galaxies on a thin plane (the ‘planes of satellites’ problem). Here we present results from apostle (A Project Of Simulating The Local Environment), a suite of cosmological hydrodynamic simulations of 12 volumes selected to match the kinematics of the Local Group (LG) members. Applying the eagle code to the LG environment, we find that our simulations match the observed abundance of LG galaxies, including the satellite galaxies of the MW and Andromeda. Due to changes to the structure of haloes and the evolution in the LG environment, the simulations reproduce the observed relation between stellar mass and velocity dispersion of individual dwarf spheroidal galaxies without necessitating the formation of cores in their dark matter profiles. Satellite systems form with a range of spatial anisotropies, including one similar to the MWs, confirming that such a configuration is not unexpected in ΛCDM. Finally, based on the observed velocity dispersion, size, and stellar mass, we provide estimates of the maximum circular velocity for the haloes of nine MW dwarf spheroidals.
The total satellite population of the Milky Way Newton, Oliver; Cautun, Marius; Jenkins, Adrian ...
Monthly Notices of the Royal Astronomical Society,
09/2018, Letnik:
479, Številka:
3
Journal Article
We present a new algorithm which groups the subhaloes found in cosmological N-body simulations by structure finders such as SUBFIND into dark matter haloes whose formation histories are strictly ...hierarchical. One advantage of these 'Dhaloes' over the commonly used friends-of-friends (FoF) haloes is that they retain their individual identity in the cases when FoF haloes are artificially merged by tenuous bridges of particles or by an overlap of their outer diffuse haloes. Dhaloes are thus well suited for modelling galaxy formation and their merger trees form the basis of the Durham semi-analytic galaxy formation model, GALFORM. Applying the Dhalo construction to the ... cold dark matter Millennium II Simulation, we find that approximately 90 per cent of Dhaloes have a one-to-one, bijective match with a corresponding FoF halo. The remaining 10 per cent are typically secondary components of large FoF haloes. Although the mass functions of both types of haloes are similar, the mass of Dhaloes correlates much more tightly with the virial mass, ..., than FoF haloes. Approximately 80 per cent of FoF and bijective and non-bijective Dhaloes are relaxed according to standard criteria. For these relaxed haloes, all three types have similar concentration-M200 relations and, at fixed mass, the concentration distributions are described accurately by log-normal distributions. (ProQuest: ... denotes formulae/symbols omitted.)
We present results from 13 cosmological simulations that explore the parameter space of the ‘Evolution and Assembly of GaLaxies and their Environments’ (EAGLE) simulation project. Four of the ...simulations follow the evolution of a periodic cube L = 50 cMpc on a side, and each employs a different subgrid model of the energetic feedback associated with star formation. The relevant parameters were adjusted so that the simulations each reproduce the observed galaxy
stellar mass function at z = 0.1. Three of the simulations fail to form disc galaxies as extended as observed, and we show analytically that this is a consequence of numerical radiative losses that reduce the efficiency of stellar feedback in high-density gas. Such losses are greatly reduced in the fourth simulation – the EAGLE reference model – by injecting more energy in higher density gas. This model produces galaxies with the observed size distribution, and also reproduces many galaxy scaling relations. In the remaining nine simulations, a single parameter or process of the reference model was varied at a time. We find that the properties of galaxies with stellar mass ≲ M
⋆ (the ‘knee’ of the galaxy stellar mass function) are largely governed by feedback associated with star formation, while those of more massive galaxies are also controlled by feedback from accretion on to their central black holes. Both processes must be efficient in order to reproduce the observed galaxy population. In general, simulations that have been calibrated to reproduce the low-redshift galaxy stellar mass function will still not form realistic galaxies, but the additional requirement that galaxy sizes be acceptable leads to agreement with a large range of observables.
We analyse the mass assembly of central galaxies in the Evolution and Assembly of Galaxies and their Environments (EAGLE) hydrodynamical simulations. We build merger trees to connect galaxies to ...their progenitors at different redshifts and characterize their assembly histories by focusing on the time when half of the galaxy stellar mass was assembled into the main progenitor. We show that galaxies with stellar mass ... assemble most of their stellar mass through star formation in the main progenitor ('in situ' star formation). This can be understood as a consequence of the steep rise in star formation efficiency with halo mass for these galaxies. For more massive galaxies, however, an increasing fraction of their stellar mass is formed outside the main progenitor and subsequently accreted. Consequently, while for low-mass galaxies, the assembly time is close to the stellar formation time, the stars in high-mass galaxies typically formed long before half of the present-day stellar mass was assembled into a single object, giving rise to the observed antihierarchical downsizing trend. In a typical present-day ... galaxy, around 20 per cent of the stellar mass has an external origin. This fraction decreases with increasing redshift. Bearing in mind that mergers only make an important contribution to the stellar mass growth of massive galaxies, we find that the dominant contribution comes from mergers with galaxies of mass greater than one-tenth of the main progenitor's mass. The galaxy merger fraction derived from our simulations agrees with recent observational estimates. (ProQuest: ... denotes formulae/symbols omitted.)
The recent detection of a 3.5 keV X-ray line from the centres of galaxies and clusters by Bulbul et al. and Boyarsky et al. has been interpreted as emission from the decay of 7 keV sterile neutrinos ...which could make up the (warm) dark matter (WDM). As part of the Copernicus Complexio
(coco) programme, we investigate the properties of dark matter haloes formed in a high-resolution cosmological N-body simulation from initial conditions similar to those expected in a universe in which the dark matter consists of 7 keV sterile neutrinos. This simulation and its cold dark matter (CDM) counterpart have ∼13.4 bn particles, each of mass ∼105 h
−1 M⊙, providing detailed information about halo structure and evolution down to dwarf galaxy mass scales. Non-linear structure formation on small scales (M
200 ≲ 2 × 109 h
−1 M⊙) begins slightly later in coco-warm than in coco-cold. The halo mass function at the present day in the WDM model begins to drop below its CDM counterpart at a mass ∼2 × 109 h
−1 M⊙ and declines very rapidly towards lower masses so that there are five times fewer haloes of mass M
200 = 108 h
−1 M⊙ in coco-warm than in coco-cold. Halo concentrations on dwarf galaxy scales are correspondingly smaller in coco-warm, and we provide a simple functional form that describes its evolution with redshift. The shapes of haloes are similar in the two cases, but the smallest haloes in coco-warm rotate slightly more slowly than their CDM counterparts.
We use the Copernicus Complexio (coco) high-resolution N-body simulations to investigate differences in the properties of small-scale structures in the standard cold dark matter (CDM) model and in a ...model with a cutoff in the initial power spectrum of density fluctuations consistent with both a thermally produced warm dark matter (WDM) particle with a rest mass of 3.3 keV and a sterile neutrino with mass 7 keV and leptogenesis parameter L sub( 6) = 8.7. The latter corresponds to the 'coldest' model with this sterile neutrino mass compatible with the identification of the recently detected 3.5 keV X-ray line as resulting from particle decay. CDM and WDM predict very different number densities of subhaloes with mass ... 10 super( 9) h super( -1) M... although they predict similar, nearly universal, normalized subhalo radial density distributions. Haloes and subhaloes in both models have cuspy Navarro-Frenk-White profiles, but WDM subhaloes below the cut-off scale in the power spectrum (corresponding to maximum circular velocities V sub( max) super( z = 0) less than or equal to 50 kms super( - 1)) are less concentrated than their CDM counterparts. We make predictions for observable properties using the galform semi-analytic model of Galaxy formation. Both models predict Milky Way satellite luminosity functions consistent with observations, although the WDM model predicts fewer very faint satellites. This model, however, predicts slightly more UV bright galaxies at redshift z > 7 than CDM, but both are consistent with observations. Gravitational lensing offers the best prospect of distinguishing between the models. (ProQuest: ... denotes formulae/symbols omitted.)
We compare global predictions from the eagle hydrodynamical simulation, and two semi-analytic (SA) models of galaxy formation, l-galaxies and galform. All three models include the key physical ...processes for the formation and evolution of galaxies and their parameters are calibrated against a small number of observables at z ≈ 0. The two SA models have been applied to merger trees constructed from the eagle dark matter only simulation. We find that at z ≤ 2, both the galaxy stellar mass functions for stellar masses M
* < 1010.5 M⊙ and the median specific star formation rates (sSFRs) in the three models agree to better than 0.4 dex. The evolution of the sSFR predicted by the three models closely follows the mass assembly history of dark matter haloes. In both eagle and l-galaxies there are more central passive galaxies with M
* < 109.5 M⊙ than in galform. This difference is related to galaxies that have entered and then left a larger halo and which are treated as satellites in galform. In the range 0 < z < 1, the slope of the evolution of the star formation rate density in eagle is a factor of ≈1.5 steeper than for the two SA models. The median sizes for galaxies with M
* > 109.5 M⊙ differ in some instances by an order of magnitude, while the stellar mass–size relation in eagle is a factor of ≈2 tighter than for the two SA models. Our results suggest the need for a revision of how SA models treat the effect of baryonic self-gravity on the underlying dark matter. The treatment of gas flows in the models needs to be revised based on detailed comparison with observations to understand in particular the evolution of the stellar mass–metallicity relation.
A unified multiwavelength model of galaxy formation Lacey, Cedric G; Baugh, Carlton M; Frenk, Carlos S ...
Monthly Notices of the Royal Astronomical Society,
11/2016, Letnik:
462, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We present a new version of the galform semi-analytical model of galaxy formation. This brings together several previous developments of galform into a single unified model, including a different ...initial mass function (IMF) in quiescent star formation and in starbursts, feedback from active galactic nuclei suppressing gas cooling in massive haloes, and a new empirical star formation law in galaxy discs based on their molecular gas content. In addition, we have updated the cosmology, introduced a more accurate treatment of dynamical friction acting on satellite galaxies, and updated the stellar population model. The new model is able to simultaneously explain both the observed evolution of the K-band luminosity function and stellar mass function, and the number counts and redshift distribution of sub-mm galaxies selected at 850 μm. This was not previously achieved by a single physical model within the Λcold dark matter framework, but requires having an IMF in starbursts that is somewhat top-heavy. The new model is tested against a wide variety of observational data covering wavelengths from the far-UV to sub-mm, and redshifts from z = 0 to 6, and is found to be generally successful. These observations include the optical and near-infrared (IR) luminosity functions, H i mass function, fraction of early type galaxies, Tully–Fisher, metallicity–luminosity and size–luminosity relations at z = 0, as well as far-IR number counts, and far-UV luminosity functions at z ∼ 3–6. Discrepancies are, however, found in galaxy sizes and metallicities at low luminosities, and in the abundance of low-mass galaxies at high-z, suggesting the need for a more sophisticated model of supernova feedback.
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