The Milky Way’s (MW) satellite population is a powerful probe of warm dark matter (WDM) models as the abundance of small substructures is very sensitive to the properties of the WDM particle. However, only a partial census of the MW’s complement of satellite galaxies exists because surveys of the MW’s close environs are incomplete both in depth and in sky coverage. We present a new Bayesian analysis that combines the sample of satellites recently discovered by the Dark Energy Survey (DES) with those found in the Sloan Digital Sky Survey (SDSS) to estimate the total satellite galaxy luminosity function down to Mv = 0. We find that there should be at least $124_{ - 27}^{ + 40}$ (68% CL, statistical error) satellites as bright or brighter than Mv = 0 within 300 kpc of the Sun, with only a weak dependence on MW halo mass. When it comes online the Large Synoptic Survey Telescope should detect approximately half of this population. We also show that WDM models infer the same number of satellites as in ΛCDM, which will allow us to rule out those models that produce insufficient substructure to be viable.

We investigate the characteristics and the time evolution of the cosmic web from redshift, z=2, to present time, within the framework of the \nexus{} algorithm. This necessitates the introduction of new analysis tools optimally suited to describe the very intricate and hierarchical pattern that is the cosmic web. In particular, we characterising filaments (walls) in terms of their linear (surface) mass density, which is very good in capturing the evolution of these structures. At early times the cosmos is dominated by tenuous filaments and sheets, which, during subsequent evolution, merge together, such that the present day web is dominated by fewer, but much more massive, structures. We show also that voids are more naturally described in terms of their boundaries and not their centres. We illustrate this for void density profiles, which, when expressed as a function of the distance from void boundary, show a universal profile in good qualitative agreement with the theoretical shell-crossing framework of expanding underdense regions.

Metal enrichment of intracluster medium (ICM) is reanalysed in the hierarchical galaxy formation scenario. In order to investigate metal abundances of $\alpha$ and iron-peak elements, we incorporate metal production processes by type Ia supernovae (SNe Ia) as well as type II supernovae (SNe II) into the GALFORM model of semi-analytic galaxy formation. We find that a top-heavy initial mass function (IMF) of stars with a power index $x\simeq 0.35$ for starburst is required under the constraint that the IMF for quiescent disc star formation is the Kennicutt IMF. Our model shows an only mild evolution of [Fe/H] as suggested by a recent observation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Modern N-body techniques allow the study of galaxy formation in the wider context of the formation of large-scale structure in the Universe. The results of such a study within the cold dark matter cosmogony are described. Dark galactic halos form at relatively recent epochs. Their properties and abundance are similar to those inferred for the halos of real galaxies. Massive halos tend to form preferentially in high density regions and as a result the galaxies that form within them are significantly more clustered than the underlying mass. This natural bias may be strong enough to reconcile the observed clustering of galaxies with the assumption that Ω = 1.

Pease and Shapley (1917) first remarked on the apparent flattening of several Galactic globular clusters, a view that has been confirmed by many subsequent studies. Tidal stresses, internal rotation, and velocity anisotropies can cause deviations from sphericity in stellar systems. In general, we might expect globular clusters to have some angular momentum at the time of formation and, if they collapsed from flattened initial conditions, to have anisotropic pressure support. Since the velocity distributions within the clusters can be altered by a variety of internal and external processes, their shapes are expected to evolve. In this article, we review the methods for measuring ellipticities and the results that have emerged from such studies. Our main purpose, however, is to discuss the processes that determine the shapes of globular clusters and the ways in which they change with time.

We have measured the ellipticities of 52 globular clusters in the LMC and 93 in the Galaxy by eye from polaroid enlargements of the sky surveys (Frenk & Fall 1982). In most cases, the measurements pertain to regions between (1–2)rh where rh is the median radius of a cluster; i.e. the radius containing half of the light in three dimensions. These were compared with determinations based on star counts for 12 members of the LMC sample and 19 members of the Galactic sample. We found no systematic difference between the ellipticities from the two methods and concluded that the eye-measurements are free of any major bias. They are also in reasonable agreement with the measurements by Geyer & Richtler (1981) and Geyer, Hopp & Nelles (1983), who used the Agfa contourfilm technique. The ellipticities measured by Geisler & Hodge (1980) from microdensitometer scans are systematically large in comparison with our results and those of Geyer and his associates. Since the scans cover only a small part of each cluster, a few bright stars can cause spurious elongations in the fitted contours.