The angular correlation function (ω(θ)) for faint, magnitude-limited samples is an important test of large scale structure formation scenarios, as well as being a valuable probe of galaxy evolution. By measuring ω(θ) one hopes to better understand the mechanism or galaxy species responsible for the number counts excess (relative to “no-evolution” models of galaxies) typically observed at blue wavelengths. Images of three ‘blank’ fields were obtained at the prime focus of the CFHT with sub-arcsecond seeing in V, R and I, to magnitude limits of 25, 24.5 and 24, respectively. The angular correlation functions calculated for one field, NF1, in V is shown in Figure 1. Clearly the amplitude of ω(θ) is decreasing at fainter magnitude limits. Note the number of objects detected are not sufficient to accurately measure ω(θ) for an individual field, in a given colour, to significantly small angular separations. In order to do this we must combine the data from our three fields and perform a multi-field fit. A full summary of this analysis will be presented in Woods et al. (1995, in prep.) including determinations of ω(θ) using galaxy samples culled from all our fields and selected by magnitude, colour and surface brightness.

We study the star formation histories of a sample of 113 nearby spiral galaxies using their radio continuum (20cm), FIR (40-120μm), H (1.65μm) and B (4400Å) luminosities. The first two are used as indicators of star formation rate over the past ∼ 108 years, as suggested by the tight and nearly universal FIR/radio correlation (Xu et al. 1994). Compared to other indicators of recent star formation rate such as Hα and UV, FIR and radio continuum have the advantage of being insensitive to extinction. The B luminosity is taken as star formation indicator for the time scale of 3 109 years, and the H luminosity for the time scale of 1010 years. We find:

1. 1. The long-term star-formation history (from a few billion years to the entire Hubble time), as indicated by the B-to-H luminosity ratio, depends strongly on the Hubble type.

2. 2. The recent star-formation history in the last a few billion years, as indicated by the radio-to-B luminosity ratio and the FIR-to-B luminosity ratio, does not depend on the Hubble type.

3. 3. Galaxies of a given Hubble type have similar long-term star-formation histories. On the other hand, their recent star-formation histories in the last a few billion years can be much different: the ratio between the star-formation rate averaged over the past 108 years to that over the past 3 109 years can be different by two orders of magnitude, as indicated by the scattering of the radio-to-B luminosity ratio and that of the FIR-to-B luminosity ratio. This is not likely to be due to the extinction on the B luminosity, because the scattering of the B-to-H luminosity ratio for a given type is much smaller.

There are evidenves which suggest that many of the early-type galaxies in rich cluster environment formed at fairly high redshift, z > 2. If the galaxies formed at such early epoch have experienced no intensive star-formation events, their photometric properties can be traced with less ambiguity by using the stellar evolutionary sinthesis models. Here we demonstrate what conspicuous feature can be observed for those passively-evolving galaxies at high redshift and how we can constrain the epoch and period of their formation.

Nearby cluster ellipticals follow a very tight relation between velocity dispersion σ and Mg absorption (e.g. Bender et al. 1993, ApJ411, 153). The small scatter in Mg implies that the age and metallicity spread at a given σ in ellipticals is smaller than 15% (applying Worthey's population synthesis models 1994, ApJS95, 107). This means that ellipticals cannot have formed continuously over the Hubble time and ongoing merger processes represent only a tail of latecomers.

We present a 67-orbit HST/WFPC2 exposure on the weak radio galaxy 53W002 at z=2.390 and its surrounding cluster. Color Plate 1 shows 12 orbits in IF814W & VF606W, and 24 in BF450W. Potential cluster members were identified through 15 orbits in F410M, optimized for narrow-band searches for compact Lyα objects at z≃2.4 (P96), and confirmed through spectroscopy (W91, P96); 16 candidates were found with significant narrow-band emission in F410M: 4 out of 5 had a confirming MMT spectroscopic redshift at z≃2.40 (P96). All are located within 60″ from 53W002, or ∼ 0.24h–1100 Mpc (qo=0.5) at z ≃2.4, the physical scale of a group or small galaxy cluster. One object contains a weak (variable) AGN, another is a merger with two companions. Their underlying young stellar population is very compact, with rh.l. ≃0.2″ (≃ 0.8h–1100 kpc), and considerably fainter than the L∗-value at z∼2.4, implying sub-galactic sized objects. These results may explain why ground-based Lya searches for PG's have been largely unsuccessful. The narrow-line galaxy 53W002 was imaged in the PC at ∼0.07″ FWHM (WK95, see also W94). Its AGN component is ≤ 20±4% of the total continuum, surrounded by an extended r1/4-envelope with rh.l. ≃1.1″ (4.3 kpc), and has an SED of ∼0.3 Gyr in the center to ∼0.5-1.0 Gyr at ∼4 kpc. A one-sided cloud is seen ∼1.8 kpc West, ∼0.3 mag bluer than the SED, aligned with the radio source and its Ly-α cloud, presumably weak scattered AGN light, and/or jet-induced star-formation.