A Group of Red, Ly-alpha Emitting, High Redshift Galaxies

We have discovered two new high redshift (z=2.38) galaxies, near the previously known z=2.38 galaxy 2139-4434 B1 (Francis et al. 1996). All three galaxies are strong Ly-alpha emitters, and have much redder continuum colors (I-K about 5) than other optically-selected high redshift galaxies. We hypothesize that these three galaxies are QSO IIs; radio-quiet counterparts of high redshift radio galaxies, containing concealed QSO nuclei. The red colors are most easily modelled by an old (> 0.5 Gyr), massive (> 10E11 solar masses) stellar population. If true, this implies that at least one galaxy cluster of mass much greater than 3E11 solar masses had collapsed before redshift five.Comment: 12 pages, 2 figures, uses aaspp4 style file. Accepted for publication in Astrophysical Journal Letter

Superclustering of damped Lyman-alpha absorption systems at redshifts above two

Two high redshift QSOs (z = 3.23 and z = 3.18) separated by 8 arcmin, and containing two strong Ly-alpha absorption systems each, were observed. In both cases, the velocities of the absorption systems between the lines of sight differ by only about 300 km/s. Low ionization metal lines are related to at least one of the absorption systems, and the neutral hydrogen column densities deduced from the profiles lie between 1.2 x 10 exp 18 and 1.2 x 10 exp 20/sq cm. The probability of observing both redshift coincidences is very low, about 0.0003. The probability of seeing the wavelength matches is increased if the absorbers are clustered. Giant gas clouds cover both lines of sight, they must have solar masses of more than 10 exp 11. These observations all hint at the presence of large dense structures in the early universe.P.J.F. is supported by a SERC/NATO advanced fellowship. Computing support was provided in part by the Starlink Project, which is funded by the UK SERC. We also thank the staff at the AAT for their invaluable assistance

The Stanford equivalence principle program

The Stanford Equivalence Principle Program (Worden, Jr. 1983) is intended to test the uniqueness of free fall to the ultimate possible accuracy. The program is being conducted in two phases: first, a ground-based version of the experiment, which should have a sensitivity to differences in rate of fall of one part in 10(exp 12); followed by an orbital experiment with a sensitivity of one part in 10(exp 17) or better. The ground-based experiment, although a sensitive equivalence principle test in its own right, is being used for technology development for the orbital experiment. A secondary goal of the experiment is a search for exotic forces. The instrument is very well suited for this search, which would be conducted mostly with the ground-based apparatus. The short range predicted for these forces means that forces originating in the Earth would not be detectable in orbit. But detection of Yukawa-type exotic forces from a nearby large satellite (such as Space Station) is feasible, and gives a very sensitive and controllable test for little more effort than the orbiting equivalence principle test itself

Low-Metallicity Gas Clouds in a Galaxy Proto-Cluster at Redshift 2.38

We present high resolution spectroscopy of a QSO whose sight-line passes through the halo of a pair of elliptical galaxies at redshift 2.38. This pair of galaxies probably lies at the center of a galaxy proto-cluster, and is embedded in a luminous extended Ly-alpha nebula. The QSO sight-line intersects two small gas clouds within this halo. These clouds have properties similar to those of high velocity clouds (HVCs) seen in the halo of the Milky Way. The gas is in a cool (< 2 x 10^4 K) and at least 20% neutral phase, with metallicities in the range -3.0 < [Fe/H] < -1.1 and neutral hydrogen column densities of ~10^19.5 /cm^2. The origin of these clouds is unclear. The presence of low metallicity gas within this possible proto-cluster implies either that the intra-cluster medium has not been enriched with metals at this redshift, or the clouds are embedded within a hot, ionized, metal-rich gas phase.Comment: Accepted to appear in ApJ Letter

Galaxy Clusters and Large Scale Structure at High Redshifts

We present a detailed study of a rich galaxy cluster at z=2.38. We demonstrate that this cluster contains large overdensities of damped Ly-alpha absorption lines, of Ly-alpha emitting galaxies and of extremely red objects. The overdensity of extremely red objects in this field demonstrates that many are high z galaxies. The huge overdensities we measure for these three classes of object are much larger than the mass overdensities of typical clusters at this redshift, as predicted by CDM and related models. We suggest therefore that the distribution of damped Ly-alpha absorption line systems, of Ly-alpha emitting galaxies and of extremely red objects are all very strongly biassed, and that somehow a small overdensity of mass has increased the fraction of baryons in collapsed objects, in the volume occupied by the cluster, to close to unity (a factor of ~10 increase). We speculate that some unknown physical process, acting on the volume occupied by our cluster, caused the normally diffuse ionised inter-galactic medium to coalesce into small (< 10^8 Solar masses) blobs of neutral hydrogen, which produce the Ly-alpha absorption-lines. Star formation occurred within these blobs at z>5, enriching them with metals and producing stars, which after several mergers and ~ 0.5 Gyr of passive evolution form the extremely red objects. The Ly-alpha emitting galaxies are probably AGN, triggered perhaps by mergers of the small blobs.Comment: Invited talk to appear in "The Young Universe", proceedings of Rome conference, ed. D'Odorico, Fontana and Giallongo. 8 pages, uses paspconf.st

Through Einsteins Eyes

We have developed a relativistically accurate computer graphics code, and have used it to produce photo-realistic images and videos of scenes where special relativistic effects dominate, either in astrophysical contexts or in imaginary worlds where the speed of light is only a few metres per second

The importance of recent infection with Mycobacterium tuberculosis in an area with high HIV prevalence: a long-term molecular epidemiological study in Northern Malawi.

BACKGROUND: The proportion of cases of tuberculosis due to recent infection can be estimated in long-term population-based studies using molecular techniques. Here, we present what is, to our knowledge, the first such study in an area with high human immunodeficiency virus (HIV) prevalence. METHODS: All patients with tuberculosis in Karonga District, Malawi, were interviewed. Isolates were genotyped using restriction-fragment-length polymorphism (RFLP) patterns. Strains were considered to be "clustered" if at least 1 other patient had an isolate with an identical pattern. RESULTS: RFLP results were available from 83% of culture-positive patients from late 1995 to early 2003. When strains with <5 bands were excluded, 72% (682/948) were clustered. Maximum clustering was reached using a 4-year window, with an estimated two-thirds of cases due to recent transmission. The proportion clustered decreased with age and varied by area of residence. In older adults, clustering was less common in men and more common in patients who were HIV positive (adjusted odds ratio, 5.1 [95% confidence interval, 2.1-12.6]). CONCLUSIONS: The proportion clustered found in the present study was among the highest in the world, suggesting high rates of recent transmission. The association with HIV infection in older adults may suggest that HIV has a greater impact on disease caused by recent transmission than on that caused by reactivation