We report the discovery of a highly significant concentration of galaxies at a redshift of z = 3.090. The structure is evident in a redshift histogram of photometrically selected "Lyman break" objects in a 9 ′ by 18 ′ field in which we have obtained 78 spectroscopic redshifts in the range 2.0 ≤ z ≤ 3.4. The dimensions of the structure projected on the plane of the sky are at least 11 ′ by 8 ′ , or 14h −1 70 by 10h −1 70 Mpc (comoving; Ω M = 1). The concentration contains 15 galaxies and one faint (R = 21.7) QSO. We consider the structure in the context of a number of cosmological models and argue that Lyman-break galaxies must be very biased tracers of mass, with an effective bias on mass scale M ∼ 10 15 M ⊙ ranging from b ∼ 2 for Ω M = 0.2 to b > ∼ 6 for Ω M = 1. In a Cold Dark Matter scenario the large bias values suggest that individual Lyman-break galaxies are associated with dark halos of mass M ∼ 10 12 M ⊙ , reinforcing the interpretation of these objects as the progenitors of massive galaxies at 1 Based in part on observations obtained at the W.M. Keck Observatory, which is operated jointly by the California Institute of Technology and the University of California.2 Alfred P. Sloan Foundation Fellow -2the present epoch. Preliminary results of spectroscopy in additional fields suggest that such large structures are common at z ∼ 3, with about one similar structure per survey field. The implied space density is consistent with the possibility that we are observing moderately rich clusters of galaxies in their early non-linear evolution. Finally, the spectrum of one of the QSOs discovered in our survey (z em = 3.356) exhibits metal line absorption systems within the 3 redshift bins having the largest number of galaxies in field, z = 2.93, 3.09, and 3.28. These results are the first from an ongoing "targeted" redshift survey designed to explore the nature and distribution of star-forming galaxies in the redshift range 2.7 < ∼ z < ∼ 3.4.

We present the first results from a program of near-infrared spectroscopy aimed at studying the familiar rest-frame optical emission lines from the H II regions of Lyman break galaxies at z ≃ 3. By targeting redshifts which bring the lines of interest into gaps between the strong OH − sky emission, we have been successful in detecting Balmer and [O III] emission lines in all five galaxies observed so far with CGS4 on UKIRT. The typical line fluxes are a few times 10 −17 erg s −1 cm −2 , approximately one order of magnitude lower than the limits reached with wide-field narrow-band imaging surveys.For a Salpeter IMF and a H 0 = 70 km s −1 Mpc −1 , q 0 = 0.1 cosmology, the

We have measured the counts-in-cells fluctuations of 268 Lyman-break galaxies with spectroscopic redshifts in six 9 ′ × 9 ′ fields at z ∼ 3. The variance of galaxy counts in cubes of comoving side length 7.7, 11.9, 11.4 h −1 100 Mpc is σ 2 gal ∼ 1.3 ± 0.4 for Ω M = 1, 0.2 open, 0.3 flat, implying a bias on these scales of σ gal /σ mass = 6.0 ± 1.1, 1.9 ± 0.4, 4.0 ± 0.7. The bias and abundance of Lyman-break galaxies are surprisingly consistent with a simple model of structure formation which assumes only that galaxies form within dark matter halos, that Lyman-break galaxies' rest-UV luminosities are tightly correlated with their dark masses, and that matter fluctuations are Gaussian and have a linear power-spectrum shape at z ∼ 3 similar to that determined locally (Γ ∼ 0.2). This conclusion is largely independent of cosmology or spectral normalization σ 8 . A measurement of the masses of Lyman-break galaxies would in principle distinguish between different cosmological scenarios.

At total Landau level filling factor νtot = 1 a double layer two-dimensional electron system with small interlayer separation supports a collective state possessing spontaneous interlayer phase coherence. This state exhibits the quantized Hall effect when equal electrical currents flow in parallel through the two layers. In contrast, if the currents in the two layers are equal, but oppositely directed, both the longitudinal and Hall resistances of each layer vanish in the low temperature limit. This finding supports the prediction that the ground state at νtot = 1 is an excitonic superfluid.The Hall effect is possibly the most widely observed phenomenon in solid state physics [1]. Owing to the Lorentz force, an ordinary current-carrying conductor in a magnetic field develops a voltage drop V H transverse to both the current I and the field. This Hall voltage is directly proportional to the magnetic field and offers a useful measure of the concentration and sign of the constituent particles responsible for conduction in the material. In more exotic systems the Hall resistance R H = V H /I can deviate strongly from this simple dependence. For example, in two-dimensional electron systems (2DES) R H exhibits ranges of magnetic field over which it is constant and precisely equal to the quantum of resistance h/e 2 divided by either an integer [2] or certain rational fractions [3]. These quantized Hall effects (QHE) reflect the presence of an energy gap in the system, due either to Landau quantization of the cyclotron orbits of the electrons or to the strong interactions between electrons in a partially filled Landau band. In superconductors, where a coherent collective electronic state is present, the Hall resistance vanishes altogether [4].In this paper we report low temperature measurements of the Hall and longitudinal resistances of a double layer 2DES in a strong perpendicular magnetic field B. Our focus is on the situation in which the total electron density N tot of the double layer system is equal to the degeneracy eB/h of a single spin-resolved Landau level produced by the magnetic field. It is well known [5] that in this ν tot = hN tot /eB = 1 case the system possesses an unusual strongly correlated phase when the separation between the two layers is less than a critical value. Owing to interlayer Coulomb interactions the critical layer separation remains non-zero even in the limit of arbitrarily weak tunneling between the layers. In this zero tunneling limit the electron system exhibits a quantized Hall effect [6] with R H = h/e 2 , a dramatically enhanced and sharply resonant zero bias tunneling conductance [7], and exact quantization of the Hall component of Coulomb drag between the layers [8]. It is well-established theoretically that the many-electron state responsible for these phe- nomena possesses an unusual broken symmetry: spontaneous interlayer phase coherence. This collective phase may be viewed in several equivalent ways, including as a Bose condensate of interlayer excitons [9] or a pseudospin f...

We have measured the angular correlation function w(h) for a sample of 871 Lyman-break galaxies (LBGs) in Ðve Ðelds at redshift z D 3. Fitting the power law to a weighted average of w(h) from A w h~b the Ðve Ðelds over the range we Ðnd arcsecb and b D 0.9. The slope is, within theA w D 2 errors, the same as for galaxy samples in the local and intermediate-redshift universe, and a slope b \ 0.25 or shallower is ruled out by the data at the 99.9% conÐdence level. Because N(z) of LBGs is well determined from 376 spectroscopic LBG redshifts, the real-space correlation function can be accurately derived from the angular one through the Limber transform. The inversion of w(h) is rather insensitive to the still relatively large uncertainties on and b, and the spatial correlation length is much A u more tightly constrained than either of these parameters. We estimate h~1 Mpc r 0 \ 3.3~0 .6 0.7(2.1~0 .5 0.4) (comoving) for (0.5) at the median redshift of the survey, (h is in units of 100 km s~1 q 0 \ 0.1 z6 \ 3.04 Mpc~1 throughout this paper). The observed comoving correlation length of LBGs at z D 3 is comparable to that of present-day spiral galaxies and is only D50% smaller than that of present-day ellipticals ; it is as large or larger than any measured in recent intermediate-redshift galaxy samples By (0.3 [ z [ 1). comparing the observed galaxy correlation length to that of the mass predicted from cold dark matter (CDM) theory, we estimate a linear bias for LBGs of b D 1.5 (4.5) for (0.5), in broad agreement q 0 \ 0.1 with our previous estimates based on preliminary spectroscopy. The strong clustering and the large bias of the LBGs are consistent with biased galaxy formation theories and provide additional evidence that these systems are associated with massive dark matter halos. The results of the clustering of LBGs at z D 3 emphasize that apparent evolution in the clustering properties of galaxies may be due as much to variations in e †ective light-to-mass bias parameter among di †erent galaxy samples as to evolution in the mass distribution through gravitational instability.