The history of large-scale structure depends on cosmological parameters and on how merging unfolds among both galaxies and groups. There has been recent evidence for clustering among Lyman-α emitters, Lyman-break galaxies, and Lyman absorbers. We present deep wide-field medium-band imaging in redshifted Lyman α of fields surrounding regions selected to have HST detections of faint Lyman α emitters, over a range of surface densities, to characterize the larger-scale environment. The radio galaxy 53W002 was previously found using HST to be part of a rich grouping at z = 2.39, including ≈ 5 spectroscopically confirmed, compact, lower-luminosity star-forming objects. Our new data show this to be part of a larger structure traced by bright active nuclei, all contained within a projected span of 6.8 ′ (3.2 Mpc). Of the 14 candidate emitters, six have been spectroscopically confirmed as active nuclei in the range z = 2.390 ± 0.008.Various statistical tests give a significance of 95-99% for the reality of this structure on the sky. Our data thus strengthen the evidence for clustering at these redshifts.The grouping around 53W002 is more extended than a relaxed King model, at the 90% confidence level. This may be evidence either for a configuration which has yet to decouple fully from the Hubble expansion, or for multiple subgroupings which will themselves at some point form a more compact, relaxed structure. The redshift range for measured members is comparable to the Hubble flow across the structure, which may imply that the structure is seen near turnaround and suggests that its mass cannot be derived from the velocity dispersion.We surveyed two additional 14 ′ fields at z = 2.4, each centered on an HST WFPC2 field which has been searched for faint Lyman α emitters, as well as -3three contiguous fields near 53W002 for objects at z ∼ 2.55. Only a single emitter consistent with showing Lyman α at z ≈ 2.4 appears in these fields, to a somewhat brighter flux limit, while a total of six candidate emitters appear in the three fields at z ∼ 2.6. Comparison with the (deeper but narrower) WFPC2 surveys suggests that the surface-density contrast from field to field is larger for brighter objects. From this survey alone, groupings such as the 53W002 "cluster" must have an area covering fraction < 0.04 in this redshift range.Three of the AGN in the structure at z = 2.4 show extended emission-line structure, with equivalent widths suggesting in situ photoionization as far as 50 kpc from the nuclei. Such objects may populate deep surveys as diffuse Lyman α emission clouds when their cores are sufficiently obscured.

-We present measurements of the spatial clustering of galaxies with stellar masses 10 11 M ⊙ , infrared luminosities 10 12 L ⊙ , and star formation rates 200M ⊙ yr −1 in two redshift intervals; 1.5 < z < 2.0 and 2 < z < 3. Both samples cluster very strongly, with spatial correlation lengths of r 0 = 14.40 ± 1.99h −1 Mpc for the 2 < z < 3 sample, and r 0 = 9.40 ± 2.24h −1 Mpc for the 1.5 < z < 2.0 sample. These clustering amplitudes are consistent with both populations residing in dark matter haloes with masses of ∼ 6×10 13 M ⊙ , making them among the most biased galaxies at these epochs. We infer, from this and previous results, that a minimum dark matter halo mass is an important factor for all forms of luminous, obscured activity in galaxies at z > 1, both starbursts and AGN. Adopting plausible models for the growth of DM haloes with redshift, then the haloes hosting the 2 < z < 3 sample will likely host the richest clusters of galaxies at z=0, whereas the haloes hosting the 1.5 < z < 2.0 sample will likely host poor to rich clusters at z=0. We conclude that ULIRGs at z 1 signpost stellar buildup in galaxies that will reside in clusters at z = 0, with ULIRGs at increasing redshifts signposting the buildup of stars in galaxies that will reside in increasingly rich clusters.

A combination of spectroscopy and broad-band photometric redshifts is used to find the complete redshift distribution of the Hercules sample of millijansky radio sources. These data are used to examine the evolution of the radio luminosity function (RLF) and its high-redshift cut-off.We report the results of recent spectroscopic observations of the Hercules sample, drawn from the 1.4-GHz Leiden -Berkeley Deep Survey (LBDS) with a flux-density limit of 1 mJy. New redshifts have been measured for 11 sources, and a further 10 were detected in continuum emission from which upper limits to the redshift are given, derived from the absence of a Lyman-limit break in their spectra. The total number of sources with known redshifts in the sample is now 47 (65 per cent). We calculated broad-band photometric redshifts for the remaining one-third of the sample, using a two-component (old stellar population plus starburst) spectral synthesis model.We use the resulting redshift distribution of this complete sample to investigate the cosmological evolution of radio sources. For the luminosity range probed by the present study ðP 1:4 GHz . 10 24:5 W Hz 21 sr 21 Þ, we use the V/ V max test to show conclusively that there is a deficit of high-redshift ðz . 2-2:5Þ objects.Comparison with the model RLFs of Dunlop & Peacock shows that our data can now exclude pure luminosity evolution as a viable description of the cosmological evolution of the RLF. However, two of the models of DP90 successfully predict the redshift-dependent evolution of the millijansky population and are approximately consistent with its observed luminosity dependence. These models, and the RLF deduced by direct binning of the data, both favour a luminosity dependence for the high-redshift cut-off, with lower luminosity sources ðP 1:4 GHz . 10 24 W Hz 21 sr 21 Þ in decline by z . 1-1:5, while higher luminosity sources ðP 1:4 GHz . 10 25-26 W Hz 21 sr 21 Þ decline in comoving number density beyond z . 2-2:5.