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We present a physically motivated semi-analytic model to understand the clustering of high redshift Lyman Alpha Emitters (LAEs). We show that the model parameters constrained by the observed luminosity functions, can be used to predict large scale bias and angular correlation function of LAEs. These predictions are shown to reproduce the observations remarkably well. We find that average masses of dark matter halos hosting LAEs brighter than threshold narrow band magnitude ~ 25 are ~ 10^11 M_\odot. These are smaller than that of typical Lyman Break Galaxies (LBGs) brighter than similar threshold continuum magnitude by a factor ~ 10. This results in a smaller clustering strength of LAEs compared to LBGs. However, using the observed relationship between UV continuum and Lyman-alpha luminosity of LAEs, we show that both LAEs and LBGs belong to the same parent galaxy population with narrow band techniques having greater efficiency in picking up galaxies with low UV luminosity. We also show that the lack of evidence for the presence of the one halo term in the observed LAE angular correlation functions can be attributed to sub-Poisson distribution of LAEs in dark matter halos as a result of their small halo occupations.

High-resolution simulations of cosmological structure formation indicate that dark matter substructure in dense environments, like groups and clusters, may survive for a long time. These dark matter subhalos are the likely hosts of galaxies. We examine the small-scale spatial clustering of subhalo major mergers at high redshift using high-resolution N-body simulations of cosmological volumes. Recently merged, massive subhalos exhibit enhanced clustering on scales ~100-300 kpc/h, relative to all subhalos of the same infall mass, for a short time after a major merger ( < 500 Myr). The small-scale clustering enhancement is smaller for lower mass subhalos, which also show a deficit on scales just beyond the excess. Halos hosting recent subhalo mergers tend to have more subhalos; for massive subhalos the excess is stronger and it tends to increase for the most massive host halos. The subhalo merger fraction is independent of halo mass for the scales we probe. In terms of satellite and central subhalos, the merger increase in small-scale clustering for massive subhalos arises from recently merged massive central subhalos having an enhanced satellite population. Our mergers are defined via their parent infall mass ratios. Subhalos experiencing major mass gains also exhibit a small-scale clustering enhancement, but these correspond to two-body interactions leading to two final subhalos, rather than subhalo coalescence.

We present measurements of the small-scale (0.1

Recent observations show a large concentration of galaxies at high redshift. At first sight strong clustering of galaxies at high redshifts seems to be in contradiction with the models of structure formation. In this paper we show that such structures are a manifestation of the strong clustering of rare peaks in the density field. We compute the frequency of occurrence of such large concentrations of galaxies in some models of structure formation.

We present constraints on the evolution of large-scale structure from a catalog of 710,000 galaxies with I_AB

The addition of deep near infrared images to the database provided by the HDF-S WFPC2 is essential to monitor the SEDs of the objects on a wide baseline and address a number of key issues including the total stellar content of baryonic mass, the effects of dust extinction, the dependence of morphology on the rest frame wavelength, the photometric redshifts, the detection and nature of extremely red objects (EROs). For these reasons deep near infrared images were obtained with the ISAAC instrument at the ESO VLT in the Js, H and Ks bands reaching, respectively, 23.5, 22.0, 22.0 limiting Vega-magnitude. A multi-color (F300, F450, F606, F814, Js, H, Ks) photometric catalog of the HDF-S has been produced. Photometric redshifts have been generated both fitting templates to the observed SEDs and with neural network techniques. Spectroscopic observations of the 9 candidates with I_AB

Together with the CMB, the three sources of information that astronomers have at high redshift as probes of the formation and evolution of the LSS are QSOs, galaxies and absorbers observed in the spectrum of distant background objects. In this contribution I try to give a hint of historical perspective, following how the technological advances have driven the emphasis from one class to another, in order to show what are the likely forthcoming milestones.

Most phenomenological galaxy formation models show a discrepancy between the predicted Tully-Fisher relation and the luminosity function. We show that this is mainly due to overmerging of galaxy haloes, which is inherent in both the Press-Schechter formalism and dissipationless N-body simulations. This overmerging problem be circumvented by including a specific galaxy halo formation recipe into an otherwise standard N-body code. Resolving the overmerging also allows us to include models for chemical evolution and starbursts, which improves the match to observational data and renders the modelling more realistic. We use high-redshift clustering data to try and distinguish models which predict similar results at low redshifts for different sets of parameters.

We discuss the theoretical interpretation of observational data concerning the clustering of galaxies at high redshifts. Building on the theoretical machinery developed by Matarrese et al. (1997), we make detailed quantitative predictions of galaxy clustering statistics for a variety of cosmological models, taking into account differences in spatial geometry and initial fluctuation spectra and exploring the role of bias as a complicating factor in these calculations. We demonstrate that the usual description of evolution (in terms of the parameters $\epsilon$ and $r_0$) is not useful for realistic galaxy clustering models. We compare the detailed predictions of the variation of correlation functions with redshift against current observational data to constrain available models of structure formation. Theories that fit the present-day abundance of rich clusters are generally compatible with the observed redshift evolution of galaxy clustering if galaxies are no more than slightly biased at $z\sim 1$. We also discuss the interpretation of a concentration of Lyman-break galaxies found by Steidel et al. (1998), coming to the conclusion that such concentrations are not unexpected in `standard' models of structure formation.

We present results from a near-infrared narrow-band survey of emission-line galaxies at z=2.23, using the Wide Field Camera on the United Kingdom Infrared Telescope. The H2S1 narrow-band filter (lambda_c=2.121um) we employ selects the H-alpha emission line redshifted to z=2.23, and is thus suitable for selecting 'typical' star forming galaxies and active galactic nuclei at this epoch. The pilot study was undertaken in the well studied Cosmological Evolution Survey field (COSMOS) and is already the largest near-infrared narrow-band survey at this depth, with a line flux limit of F(H-alpha)~10^-16 erg/s/cm^2 over 0.60 square degrees, probing ~220x10^3 Mpc^3 (co-moving) down to a limiting star formation rate of 30 M_sun/yr (3sigma). In this paper we present the results from our pilot survey and evaluate the H-alpha luminosity function and estimate the clustering properties of H-alpha emitters at z=2.23 from 55 detected galaxies. The integrated luminosity function is used to estimate the volume averaged star formation rate at z=2.23: SFRD = 0.17^{+0.16}_{-0.09} M_sun/yr/Mpc^3 for L(H-alpha) > 10^42 erg/s. For the first time, we use the H-alpha star-formation tracer to reliably constrain SFRD out to z=2.23 demonstrating the rapid increase in SRFD out to this redshift as well as confirming the flattening in SFRD between z~1-2. In addition to the luminosity distribution, we analyse the clustering properties of these galaxies. Using the 2-point angular correlation function, we estimate a real space correlation length of r_0= 4.2^{+0.4}_{-0.2} h^-1 Mpc. In comparison to models of clustering which take into account bias evolution, we estimate that these galaxies are hosted by dark matter halos of mass M_halo ~ 10^12 M_sun consistent with the progenitors of the Milky Way.

We use a suite of high-resolution N-body simulations to study the properties, abundance and clustering of high mass halos at high redshift, including their mass assembly histories and mergers. We find that the analytic form which best fits the abundance of halos depends sensitively on the assumed definition of halo mass, with common definitions of halo mass differing by a factor of two for these low concentration, massive halos. A significant number of massive halos are undergoing rapid mass accretion, with major merger activity being common. We compare the mergers and mass accretion histories to the extended Press-Schechter formalism. We consider how major merger induced star formation or black hole accretion may change the distribution of photon production from collapsed halos, and hence reionization, using some simplified examples. In all of these, the photon distribution for a halo of a given mass acquires a large scatter. If rare, high mass halos contribute significantly to the photon production rates, the scatter in photon production rate can translate into additional scatter in the sizes of ionized bubbles.

This paper reviews the current status of measurements of galaxy clustering at high redshifts (z > 0.3). The focus is on the inherent limitations in the observation and interpretation of the ``evolution of clustering''. It is likely that results from the first attempts to characterize galaxy clustering beyond the ``local'' universe have been significantly limited by sample variance, as the difficulty in assembling large samples over large volumes is exacerbated as the observations become more challenging. It is also argued that, because of the complicated relationship between galaxies and mass (i.e., bias), and the surprising degeneracies among different popular cosmological models, it is likely that studies of galaxy clustering as a function of cosmic epoch will never be useful for strong discrimination between different cosmological models. On the other hand, observations of galaxy clustering are capable of testing basic ideas about how (and where) galaxies form. Galaxy formation, as opposed to cosmography, will probably remain a fundamental question even beyond the MAP and Planck era.