We discuss the non-linear evolution of the angular momentum L acquired by protostructures, like protogalaxies and protoclusters, due to tidal interactions with the surrounding matter inhomogeneities. ...The primordial density distribution is assumed to be Gaussian, and the non-linear dynamics of the collisionless mass fluid is followed using Lagrangian perturbation theory. For a cold dark matter spectrum, the inclusion of the leading-order Lagrangian correction terms results in a value of the rms ensemble average 〈L,2〉1/2 which is only a factor of 1.3 higher than the corresponding linear estimate, irrespective of the scale. Consequently, the predictions of linear theory are rather accurate in quantifying the evolution of the angular momentum of protostructures before collapse sets in. In the Einstein-de Sitter universe, the initial torque is a good estimate for the tidal torque over the whole period during which the object is spun up.
Models for the formation of galaxies and clusters of galaxies require strong feedback in order to explain the observed properties of these systems. We investigate whether such feedback has ...observational consequences for the intergalactic medium, as probed in absorption towards background quasars. A typical quasar sight-line intersects one protocluster per unit redshift, and significant feedback from forming galaxies or active galactic nuclei, heating the protocluster gas, will result in a large clearing of reduced absorption in the Lyα forest. Such a gap could be detected at redshift ≳3 when the mean opacity is high. Feedback from Lyman-break galaxies in protoclusters can be probed by the absorption lines produced in their winds. Strong feedback from galaxies has a major impact on the number and properties of absorption lines with column densities NH i∼1016 cm−2. This feedback can be probed with multiple sight-lines and by studying the unsaturated higher order lines of the Lyman series. Galactic winds from dwarf galaxies should break up into clouds, in order not to overproduce the number of absorption lines. These clouds can then coast to large distances.
Abstract
We study the ability of PINOCCHIO (PINpointing Orbit-Crossing Collapsed HIerarchical Objects) to predict the merging histories of dark matter (DM) haloes, comparing the PINOCCHIO predictions ...with the results of two large N-body simulations run from the same set of initial conditions. We focus our attention on the quantities most relevant to galaxy formation and large-scale structure studies. PINOCCHIO is able to predict the statistics of merger trees with a typical accuracy of 20 per cent. Its validity extends to higher-order moments of the distribution of progenitors. The agreement is also valid at the object-by-object level, with 70-90 per cent of the progenitors cleanly recognized when the parent halo is cleanly recognized itself. Predictions are also presented for quantities that are usually not reproduced by semi-analytic codes, such as the two-point correlation function of the progenitors of massive haloes and the distribution of initial orbital parameters of merging haloes. For the accuracy of the prediction and for the facility with which merger histories are produced, PINOCCHIO provides a means to generate catalogues of DM haloes, which is extremely competitive with large-scale N-body simulations, making it a suitable tool for galaxy formation and large-scale structure studies.
Intergalactic stars in the Fornax cluster Theuns, Tom; Warren, S. J.
Monthly notices of the Royal Astronomical Society,
01/1997, Letnik:
284, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We have identified 10 candidate intergalactic planetary nebulae in the Fornax galaxy cluster. These objects were found during observations in 1992 and 1993 in three fields chosen well away from any ...Fornax galaxy at 15,30 and 45 arcmin from the centre of Fornax. We used the usual method of blinking images taken in a narrow O iii X5007-Å filter with images taken in an adjacent broad filter. The measured fluxes in the narrow, broad and I bands are consistent with these unresolved objects being planetary nebulae immersed in an intergalactic population of stars. Such a population is expected to arise as a consequence of tidal encounters between galaxies, and our findings strengthen the case for the existence of such tidal debris. The confirmation of some or all of these 10 candidates as planetary nebulae would imply that intergalactic stars constitute a substantial fraction of all the stars in Fornax, up to an estimated Ȓ40 per cent. Intergalactic planetary nebulae could prove useful in probing the underlying cluster potential, since they would be far more abundant than galaxies. We discuss possible contamination of the sample by emission-line galaxies, but conclude that planetary nebulae comprise the most likely identification for the detected objects.
The temperature of the intergalactic medium (IGM) is an important factor in determining the linewidths of the absorption lines in the Lyα forest. We present a method to characterize the linewidth ...distribution using a decomposition of an Lyα spectrum in terms of discrete wavelets. Such wavelets form an orthogonal basis, so the decomposition is unique. We demonstrate using hydrodynamic simulations that the mean and dispersion of the wavelet amplitudes are strongly correlated with both the temperature of the absorbing gas and its dependence on the gas density. Since wavelets are also localized in space, we are able to analyse the temperature distribution as a function of position along the spectrum. We illustrate how this method could be used to identify fluctuations in the IGM temperature that might result from late reionization or local effects.
We have measured redshifts for 243 z approximate to 3 quasars in nine Very Large Telescope (VLT) Visible Imaging and Multi-Object Spectrograph (VIMOS) Lyman-break galaxy (LBG) redshift survey areas, ...each of which is centred on a known bright quasar. Using the spectra of these quasars, we measure the cross-correlation between neutral hydrogen gas causing the Ly alpha forest and 1020 LBGs at z approximate to 3. We find an increase in neutral hydrogen absorption within approximate to 5 h(-1) Mpc of a galaxy in agreement with the results of Adelberger et al. The Ly alpha-LBG cross-correlation can be described by a power law on scales larger than 3 h(-1) Mpc. When galaxy velocity dispersions are taken into account, our results at smaller scales (\textless2 h(-1) Mpc) are also in good agreement with the results of Adelberger et al. There is little immediate indication of a region with a transmission spike above the mean intergalactic medium value which might indicate the presence of star formation feedback. To measure the galaxy velocity dispersions, which include both intrinsic LBG velocity dispersion and redshift errors, we have used the LBG-LBG redshift-space distortion measurements of Bielby et al. We find that the redshift-space transmission spike implied in the results of Adelberger et al. is too narrow to be physical in the presence of the likely LBG velocity dispersion and is likely to be a statistical fluke. Nevertheless, neither our nor previous data can rule out the presence of a narrow, real-space transmission spike, given the evidence of the increased Ly alpha absorption surrounding LBGs which can mask the spike's presence when convolved with a realistic LBG velocity dispersion. Finally, we identify 176 C IV systems in the quasar spectra and find an LBG-CIV correlation strength on scales of 10 h(-1) Mpc consistent with the relation measured at approximate to Mpc scales.
We present the public data release of halo and galaxy catalogues extracted from the eagle suite of cosmological hydrodynamical simulations of galaxy formation. These simulations were performed with ...an enhanced version of the gadget code that includes a modified hydrodynamics solver, time-step limiter and subgrid treatments of baryonic physics, such as stellar mass loss, element-by-element radiative cooling, star formation and feedback from star formation and black hole accretion. The simulation suite includes runs performed in volumes ranging from 25 to 100 comoving megaparsecs per side, with numerical resolution chosen to marginally resolve the Jeans mass of the gas at the star formation threshold. The free parameters of the subgrid models for feedback are calibrated to the redshift z=0 galaxy stellar mass function, galaxy sizes and black hole mass–stellar mass relation. The simulations have been shown to match a wide range of observations for present-day and higher-redshift galaxies. The raw particle data have been used to link galaxies across redshifts by creating merger trees. The indexing of the tree produces a simple way to connect a galaxy at one redshift to its progenitors at higher redshift and to identify its descendants at lower redshift. In this paper we present a relational database which we are making available for general use. A large number of properties of haloes and galaxies and their merger trees are stored in the database, including stellar masses, star formation rates, metallicities, photometric measurements and mock gri images. Complex queries can be created to explore the evolution of more than 105 galaxies, examples of which are provided in the Appendix. The relatively good and broad agreement of the simulations with a wide range of observational datasets makes the database an ideal resource for the analysis of model galaxies through time, and for connecting and interpreting observational datasets.
We use an array of high-resolution N-body simulations to determine the mass function of dark matter haloes at redshifts 10–30. We develop a new method for compensating for the effects of finite ...simulation volume that allows us to find an approximation to the true ‘global’ mass function. By simulating a wide range of volumes at different mass resolution, we calculate the abundance of haloes of mass 105−12 h−1 M⊙. This enables us to predict accurately the abundance of the haloes that host the sources that reionize the Universe. In particular, we focus on the small mass haloes (≳105.5−6 h−1 M⊙) likely to harbour Population III stars where gas cools by molecular hydrogen emission, early galaxies in which baryons cool by atomic hydrogen emission at a virial temperature of ∼104K (∼107.5−8 h−1 M⊙), and massive galaxies that may be observable at redshift ∼10. When we combine our data with simulations that include high-mass haloes at low redshift, we find that the best fit to the halo mass function depends not only on the linear overdensity, as is commonly assumed in analytic models, but also on the slope of the linear power spectrum at the scale of the halo mass. The Press–Schechter model gives a poor fit to the halo mass function in the simulations at all epochs; the Sheth-Tormen model gives a better match, but still overpredicts the abundance of rare objects at all times by up to 50 per cent. Finally, we consider the consequences of the recently released WMAP 3-yr cosmological parameters. These lead to much less structure at high redshift, reducing the number of z= 10‘mini-haloes’ by more than a factor of two and the number of z= 30 galaxy hosts by nearly four orders of magnitude. Code to generate our best-fitting halo mass function may be downloaded from http://icc.dur.ac.uk/Research/PublicDownloads/genmf_readme.html.
The energy diffusion coefficients Dn(E) = ⟨E(E)n/Δt⟩ (n = l, 2) for a system of equal-mass particles moving self-consistently in an N-body realization of a King model are computed from the ...probability per unit time, ℘(E,ΔE)dE dΔE, that a star with initial energy E will undergo an energy change ΔE. In turn, ℘ is computed from the number of times during the simulation that a particle in a ‘state’ of given energy undergoes a transition to another state. These particle ‘states’ are defined directly from the time evolution of E by identifying them with the event occurring between two local maxima in the E (t) curve. If one assumes next that energy changes are uncorrelated between different states, one can use diffusion theory to compute Dn(E). The simulations employ N=512, 2048, … 32768 particles and are performed using an implementation of Aarseth's direct integrator Nbody1 on a massively parallel computer. The more than seven million transitions measured in the largest N simulation provide excellent statistics. The numerically determined D(E)s are compared against their theoretical counterparts, which are computed from phase-space-averaged rates of energy change due to independent binary encounters. The overall agreement between them is impressive over most of the energy range, notwithstanding the very different type of approximations involved, giving considerable support to the valid usage of these theoretical expressions to simulate dynamical evolution in Fokker-planck-type calculations. Even so, diffusion, as judged from these measurements of the diffusion constants, is stronger than expected from theory, in both core and outer halo, by a factor up to 2, rather independent of particle number. The experimental Ds obey very well the expected scaling as N/ln ∧ with particle number N.
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