We present extensive optical and infrared photometry of the afterglow of gamma-ray burst (GRB) 030329 and its associated supernova (SN) 2003dh over the first two months after detection (2003 March 30-May 29 UT). Optical spectroscopy from a variety of telescopes is shown and, when combined with the photometry, allows an unambiguous separation between the afterglow and supernova contributions. The optical afterglow of the GRB is initially a power-law continuum but shows significant color variations during the first week that are unrelated to the presence of a supernova. The early afterglow light curve also shows deviations from the typical power-law decay. A supernova spectrum is first detectable ∼ 7 days after the burst and dominates the light after ∼ 11 days. The spectral evolution and the light curve are shown to closely resemble those of SN 1998bw, a peculiar Type Ic SN associated with GRB 980425, and the time of the supernova explosion is close to the observed time of the GRB. It is now clear that at least some GRBs arise from core-collapse SNe.

A B S T R A C TWe simulate the formation and evolution of the local galaxy population, starting from initial conditions with a smoothed linear density field which matches that derived from the IRAS 1.2-Jy galaxy survey. Our simulations track the formation and evolution of all dark matter haloes more massive than 10 11 M ( out to a distance of 8000 km s 21 from the Milky Way. We implement prescriptions similar to those of Kauffmann et al. to follow the assembly and evolution of the galaxies within these haloes. We focus on two variants of the CDM cosmology: a LCDM model and a tCDM model. Galaxy formation in each is adjusted to reproduce the I-band Tully-Fisher relation of Giovanelli et al. We compare the present-day luminosity functions, colours, morphology and spatial distribution of our simulated galaxies with those of the real local population, in particular with the Updated Zwicky Catalog, with the IRAS PSCz redshift survey, and with individual local clusters such as Coma, Virgo and Perseus. We also use the simulations to study the clustering bias between the dark matter and galaxies of differing type. Although some significant discrepancies remain, our simulations recover the observed intrinsic properties and the observed spatial distribution of local galaxies reasonably well. They can thus be used to calibrate methods which use the observed local galaxy population to estimate the cosmic density parameter or to draw conclusions about the mechanisms of galaxy formation. To facilitate such work, we publicly release our z ¼ 0 galaxy catalogues, together with the underlying mass distribution.

We use simulations of the formation and evolution of the galaxy population in the local Universe to address the issue of whether the standard theoretical model succeeds in producing empty regions as large and as dark as those observed nearby. We follow the formation of galaxies in a cold dark matter universe and work with mock catalogues that can resolve the morphology of Large Magellanic Cloud sized galaxies, and the luminosity of objects six times fainter. We look for a void signature in sets of virialized haloes selected by mass, and in mock galaxy samples selected according to observationally relevant quantities, such as luminosity, colour or morphology. We find several void regions with diameter 10 h −1 Mpc in the simulation where gravity seems to have swept away even the smallest haloes we were able to track. We probe the environment density for the various populations and compute luminosity functions for galaxies residing in underdense, mean density and overdense regions. We also use nearest-neighbour statistics to check possible void populations, taking L * spirals as reference neighbours. Down to our resolution limits, we find that all types of galaxies avoid the same regions, and that no class appears to populate the voids defined by the bright galaxies.

The Monge-Ampere-Kantorovich (MAK) reconstruction is tested against cosmological N-body simulations. Using only the present mass distribution sampled with particles, and the assumption of homogeneity of the primordial distribution, MAK recovers for each particle the non-linear displacement field between its present position and its Lagrangian position on a primordial uniform grid. To test the method, we examine a standard LCDM N-body simulation with Gaussian initial conditions and 6 models with non-Gaussian initial conditions: a chi-squared model, a model with primordial voids and four weakly non-Gaussian models. Our extensive analyses of the Gaussian simulation show that the level of accuracy of the reconstruction of the nonlinear displacement field achieved by MAK is unprecedented, at scales as small as about 3 Mpc. In particular, it captures in a nontrivial way the nonlinear contribution from gravitational instability, well beyond the Zel'dovich approximation. This is also confirmed by our analyses of the non-Gaussian samples. Applying the spherical collapse model to the probability distribution function of the divergence of the displacement field, we also show that from a well-reconstructed displacement field, such as that given by MAK, it is possible to accurately disentangle dynamical contributions induced by gravitational clustering from possible initial non-Gaussianities, allowing one to efficiently test the non-Gaussian nature of the primordial fluctuations. In addition, a simple application of MAK using the Zel'dovich approximation allows one to also recover accurately the present-day peculiar velocity field on scales of about 8 Mpc.Comment: Version to appear in MNRAS, 24 pages, 21 figures appearing (uses 35 figure files), 1 tabl

We address the degree and rapidity of generation of small‐scale power over the course of structure formation in cosmologies where the primordial power spectrum is strongly suppressed beyond a given wavenumber. We first summarize the situations where one expects such suppressed power spectra and point out their diversity. We then employ an exponential cut‐off, which characterizes warm dark matter (WDM) models, as a template for the shape of the cut‐off and focus on damping scales ranging from 106 to 109 h−1 M⊙. Using high‐resolution simulations, we show that the suppressed part of the power spectrum is quickly (re)generated and catches up with both the linear and the non‐linear evolution of the unsuppressed power spectrum. From z= 2 onwards, a power spectrum with a primordial cut‐off at 109 h−1 M⊙ becomes virtually indistinguishable from an evolved cold dark matter (CDM) power spectrum. An attractor such as that described in Zaldarriaga, Scoccimarro & Hui for power spectra with different spectral indices also emerges in the case of truncated power spectra. Measurements of z∼ 0 non‐linear power spectra at ∼100 h−1 kpc cannot rule out the possibility of linear power spectra damped below ∼109 h−1 M⊙. Therefore, WDM or scenarios with similar features should be difficult to exclude in this way.