The deepest region of the ROSAT All−Sky Survey, at the North Ecliptic Pole, has been studied to produce a complete and unbiased X-ray selected sample of clusters of galaxies. This sample is used to investigate the nature of cluster evolution and explore potential implications for large-scale structure models. The survey is 99.6% optically identified. Spectroscopic redshifts have been measured f...

We investigate various probes of luminosity evolution in the rich cluster environment, concentrating in particular on the spheroidal (E/S0) galaxies, using a newly-constructed catalog of morphologically-classified Hubble Space Telescope (HST) images of galaxies observed in the cores of 13 clusters with redshifts 0.17 ≤ z ≤ 0.56. An important distinction of this study compared to earlier work is...

We trace the evolution of central galaxies in three ∼ 10 M⊙ galaxy groups simulated at high resolution in cosmological hydrodynamical simulations. In all three cases, the evolution in the group potential leads, at z = 0, to central galaxies that are massive, gas-poor early-type systems supported by stellar velocity dispersion resembling either elliptical or S0 galaxies, even without including e...

In this review I demonstrate that a realistic model for the formation of galaxy disks depends on a proper treatment of the gas in galaxies. Historically, cosmological simulations of disk galaxy formation have suffered from a lack of resolution and a physically motivated feedback prescription. Recent computational progress has allowed for unprecedented resolution, which in turn allows for a more...

The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass funct...

We present the kinematic properties of a tidally disrupted dwarf galaxy in the Milky Way, based on the hypothesis that its central part once contained the most massive Galactic globular cluster, ω Cen. Dynamical evolution of a selfgravitating progenitor galaxy that follows the present-day and likely past orbits of ω Cen is calculated numerically and the kinematic nature of their tidal debris is...

Understanding the Milky Way structure and evolution is a major objective in astrophysics. Our Galaxy is an object of highest interest for learning about galaxy formation and evolution in general. Many data of different kinds (photometry, astrometry, spectroscopy) are available for millions of stars in the Milky Way, which interpretation in terms of evolution is not easy. Stars in the Milky Way ...

THE ROLE OF STELLAR FEEDBACK IN GALAXY EVOLUTION

Extremely Red Objects (EROs) offer a window to the universe at z ∼ 1 analogous to that provided by the Lyman Break galaxies at z = 3. Passive evolution and hierarchical galaxy formation models make very distinct predictions for the K (2.2μm) surface density of galaxies at z ∼ 1 and EROs are a powerful constraint on these theories. I present a study of nine resolved EROs with R − K ≥ 5.3 and K ≤...

The unprecedented detail of the WFPC2 colour-magnitude diagrams of the resolved stellar population of Leo A presented here allows us to determine a new distance and an accurate star formation history for this extremely metal-poor Local Group dwarf irregular galaxy. From the position of the red clump, the helium-burning blue loops and the tip of the red giant branch, we obtain a distance modulus...