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Register a new userMilky Way type galaxies in a LCDM cosmology
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Added by
Maria Emilia De Rossi
Publication date
2009
fields
Physics
and research's language is
English
Authors
Maria E. De Rossi
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We analyse a sample of 52,000 Milky Way (MW) type galaxies drawn from the publicly available galaxy catalogue of the Millennium Simulation with the aim of studying statistically the differences and similarities of their properties in comparison to our Galaxy. Model galaxies are chosen to lie in haloes with maximum circular velocities in the range 200-250 km/seg and to have bulge-to-disk ratios similar to that of the Milky Way. We find that model MW galaxies formed quietly through the accretion of cold gas and small satellite systems. Only 12 per cent of our model galaxies experienced a major merger during their lifetime. Most of the stars formed in situ, with only about 15 per cent of the final mass gathered through accretion. Supernovae and AGN feedback play an important role in the evolution of these systems. At high redshifts, when the potential wells of the MW progenitors are shallower, winds driven by supernovae explosions blow out a large fraction of the gas and metals. As the systems grow in mass, SN feedback effects decrease and AGN feedback takes over, playing a more important role in the regulation of the star formation activity at lower redshifts. Although model Milky Way galaxies have been selected to lie in a narrow range of maximum circular velocities, they nevertheless exhibit a significant dispersion in the final stellar masses and metallicities. Our analysis suggests that this dispersion results from the different accretion histories of the parent dark matter haloes. Statically, we also find evidences to support the Milky Way as a typical Sb/Sc galaxy in the same mass range, providing a suitable benchmark to constrain numerical models of galaxy formation
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We apply a semi-analytic galaxy formation model to two high resolution cosmological N-body simulations to investigate analogues of the Milky Way system. We select these according to observed properties of the Milky Way rather than by halo mass as in most previous work. For disk-dominated central galaxies with stellar mass (5--7) x 10d10Msun, the median host halo mass is 1.4 x 10d12Msun, with 1 sigma dispersion in the range [0.86, 3.1] x 10d12Msun, consistent with dynamical measurements of the Milky Way halo mass. For any given halo mass, the probability of hosting a Milky Way system is low, with a maximum of ~20% in haloes of mass ~10d12Msun. The model reproduces the V-band luminosity function and radial profile of the bright (MV < -9) Milky Way satellites. Galaxy formation in low mass haloes is found to be highly stochastic, resulting in an extremely large scatter in the relation between MV (or stellar mass) for satellites and the depth of the subhalo potential well in which they live, as measured by the maximum of the rotation curve, Vmax. We conclude that the too big to fail problem is an artifact of selecting satellites in N-body simulations according to subhalo properties: in 10% of cases we find that three or fewer of the brightest (or most massive) satellites have Vmax > 30 km/s. Our model predicts that around half of the dark matter subhaloes with Vmax > 20 km/s host satellites fainter than MV = -9 and so may be missing from existing surveys.
Our knowledge about galaxy evolution comes from transforming observed galaxy properties at different redshifts to co-moving physical scales. This transformation depends on using a cosmological model. Here the effects of unintentional mixing of two different cosmological models on the size evolution of galaxies is studied. As a gedanken experiment, a galaxy of fixed proper size and luminosity is moved across different redshifts. The apparent size of this galaxy is then interpreted with a cosmological model presumed by the observer, which is different compared to the cosmology exhibited by the Universe. In such a case, a spurious size evolution of the galaxy is observed. A galaxy behaving according to the R_h=ct and Neumanns cosmology, when interpreted with the LCDM cosmological model, shows an increase in size by a factor of 1.1 and 1.3 from z=7.5 to z approx. 0, respectively. The apparent size of a galaxy in a static Euclidean cosmology, when interpreted in the LCDM model, shows a factor of 23.8 increase in size between z=7.5 to z approx. 0. This is in close agreement with the observational data with a size increase of a factor of 6.8 between z=3.2 to z approx. 0. Furthermore, using the apparent size data, it is shown that the difference between the derived proper sizes in R_h=ct, Neumanns and LCDM cosmological models are minimal.
We introduce a dust model for cosmological simulations implemented in the moving-mesh code AREPO and present a suite of cosmological hydrodynamical zoom-in simulations to study dust formation within galactic haloes. Our model accounts for the stellar production of dust, accretion of gas-phase metals onto existing grains, destruction of dust through local supernova activity, and dust driven by winds from star-forming regions. We find that accurate stellar and active galactic nuclei feedback is needed to reproduce the observed dust-metallicity relation and that dust growth largely dominates dust destruction. Our simulations predict a dust content of the interstellar medium which is consistent with observed scaling relations at $z = 0$, including scalings between dust-to-gas ratio and metallicity, dust mass and gas mass, dust-to-gas ratio and stellar mass, and dust-to-stellar mass ratio and gas fraction. We find that roughly two-thirds of dust at $z = 0$ originated from Type II supernovae, with the contribution from asymptotic giant branch stars below 20 per cent for $z gtrsim 5$. While our suite of Milky Way-sized galaxies forms dust in good agreement with a number of key observables, it predicts a high dust-to-metal ratio in the circumgalactic medium, which motivates a more realistic treatment of thermal sputtering of grains and dust cooling channels.
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We study the concentration of dark matter halos and its evolution in N-body simulations of the standard LCDM cosmology. The results presented in this paper are based on 4 large N-body simulations with about 10 billion particles each: the Millennium-I and II, Bolshoi, and MultiDark simulations. The MultiDark (or BigBolshoi) simulation is introduced in this paper. This suite of simulations with high mass resolution over a large volume allows us to compute with unprecedented accuracy the concentration over a large range of scales (about six orders of magnitude in mass), which constitutes the state-of-the-art of our current knowledge on this basic property of dark matter halos in the LCDM cosmology. We find that there is consistency among the different simulation data sets. We confirm a novel feature for halo concentrations at high redshifts: a flattening and upturn with increasing mass. The concentration c(M,z) as a function of mass and the redshift and for different cosmological parameters shows a remarkably complex pattern. However, when expressed in terms of the linear rms fluctuation of the density field sigma(M,z), the halo concentration c(sigma) shows a nearly-universal simple U-shaped behaviour with a minimum at a well defined scale at sigma=0.71. Yet, some small dependences with redshift and cosmology still remain. At the high-mass end (sigma < 1) the median halo kinematic profiles show large signatures of infall and highly radial orbits. This c-sigma(M,z) relation can be accurately parametrized and provides an analytical model for the dependence of concentration on halo mass. When applied to galaxy clusters, our estimates of concentrations are substantially larger -- by a factor up to 1.5 -- than previous results from smaller simulations, and are in much better agreement with results of observations. (abridged)
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