In this review article, we discuss the current status of particle dark matter, including experimental evidence and theoretical motivations. We discuss a wide array of candidates for particle dark matter, but focus on neutralinos in models of supersymmetry and Kaluza-Klein dark matter in models of universal extra dimensions. We devote much of our attention to direct and indirect detection techniques, the constraints placed by these experiments and the reach of future experimental efforts. FERMILAB-Pub-04/047-A hep-ph/0404175• T ∼ 1 eV. The matter density becomes equal to that of the radiation, allowing for the formation of structure to begin.• T ∼ 0.4 eV. Photon decoupling produces the cosmic background radiation (CMB), discussed in Sec. 2.3.

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The minimum mass that a virialized gas cloud must have in order to be able to cool in a Hubble time is computed, using a detailed treatment of the chemistry of molecular hydrogen. With a simple model for halo proÐles, we reduce the problem to that of numerically integrating a system of chemical equations. The results agree well with numerically expensive three-dimensional simulations, and our approach has the advantage of being able to explore large regions of parameter space rapidly. The minimum baryonic mass is found to be strongly redshift dependent, dropping from at z D 15 to atas molecular cooling becomes e †ective. For z ? 100, rises again, as cosmic microwave back-M b ground photons inhibit formation through the H~channel. Finally, for z ? 200, the channel for H 2 H 2 formation becomes e †ective, driving down toward With a standard cold dark H 2 M b M b D 103 M _ . matter power spectrum with this implies that a fraction 10~3 of all baryons may have formed p 8 \ 0.7, luminous objects by z \ 30, which could be sufficient to reheat the universe.

The definitive version is available at www.blackwell-synergy.com. Copyright Blackwell PublishingA major amendment in recent models of hierarchical galaxy formation is the inclusion of so-called active galactic nucleus (AGN) feedback. The energy input from an active central massive black hole is invoked to suppress star formation in early-type galaxies at later epochs. A major problem is that this process is poorly understood, and compelling observational evidence for its mere existence is still missing. In search for signatures of AGN feedback, we have compiled a sample of 16 000 early-type galaxies in the redshift range 0.05 200 km s ) and roughly evenly distributed between star formation and AGN at intermediate and low (?? <100 km s ) masses. The objects with emission (???20 per cent) are offset from the red sequence and form a well-defined pattern in the colour-mass diagram. Star-forming early-types inhabit the blue cloud, while early-types with AGN are located considerably closer to and almost on the red sequence. Star formation-AGN composites are found right between these two extremes. We further derive galaxy star formation histories using a novel method that combines multiwavelength photometry from near-ultraviolet (UV) to near-infrared (IR) and stellar absorption indices. We find that in those objects deviating from the red sequence star formation occurred several 100 Myr in the past involving 1-10 per cent of the total stellar mass. We identify an evolutionary sequence from star formation via nuclear activity to quiescence. This transition process lasts about 1 Gyr, and the peak AGN phase occurs roughly half a Gyr after the starburst. The most likely interpretation is that star formation is suppressed by nuclear activity in these objects before they settle on the red sequence. This is empirical evidence for the occurrence of AGN feedback in early-type galaxies at recent epochs. ?? 2007 The Authors. Journal compilation ?? 2007 RAS

The definitive article can be found at: http://www3.interscience.wiley.com/ Copyright Royal Astronomical SocietyThe environment is known to affect the formation and evolution of galaxies considerably best visible through the well-known morphology???density relationship. It is less clear, though, whether the environment is equally important at a given galaxy morphology. In this paper, we study the effect of environment on the evolution of early-type galaxies as imprinted in the fossil record by analysing the stellar population properties of 3360 galaxies morphologically selected by visual inspection from the Sloan Digital Sky Survey in a narrow redshift range ( 0.05 ???z??? 0.06 ). The morphological selection algorithm is critical, as it does not bias against recent star formation. We find that the distribution of ages is bimodal with a strong peak at old ages and a secondary peak at young ages around ???2.5 Gyr containing about 10 per cent of the objects. This is an analogue to 'red sequence' and 'blue cloud' identified in galaxy populations usually containing both early- and late-type galaxies. The fraction of the young, rejuvenated galaxies increases with both decreasing galaxy mass and decreasing environmental density up to about 45 per cent, which implies that the impact of environment increases with decreasing galaxy mass. The rejuvenated galaxies have lower ??/Fe ratios than the average and most of them show signs of ongoing star formation through their emission line spectra. All objects that host active galactic nuclei in their centres without star formation are part of the red sequence population. We confirm and statistically strengthen earlier results that luminosity weighted ages, metallicities and ??/Fe element ratios of the red sequence population correlate well with velocity dispersion and galaxy mass. Most interestingly, however, these scaling relations are not sensitive to environmental densities and are only driven by galaxy mass. We infer that early-type galaxy formation has undergone a phase transition a few billion years ago around z??? 0.2 . A self-regulated formation phase without environmental dependence has recently been superseded by a rejuvenation phase, in which the environment plays a decisive role possibly through galaxy mergers and interactions