We have analyzed the shape of the Fundamental Plane (FP) for a sample of 226 E and S0 galaxies in ten clusters of galaxies. We nd that the distribution of galaxies is well approximated by a plane of the form log r e = 1:24 log 0:82log e + for photometry obtained in Gunn r. This result is in good agreement with previous determinations. The FP has a scatter of 0.084 in logr e . For galaxies with velocity dispersion larger than 100km s 1 the scatter is 0.073. If the FP is used for distance determinations this scatter is equivalent to 17% uncertainties on distances to single galaxies. We nd that the slope of the FP is not signi cantly di erent from cluster to cluster. Selection e ects and measurement errors can introduce biases in the derived slope. The residuals of the FP correlate weakly with the velocity dispersion and the surface brightness. Some of the coe cients used in the literature give rather strong correlations between the residuals and absolute magnitudes. This implies that galaxies need to be selected in a homogeneous way to avoid biases of derived distances on the level of 5{10% or smaller. The FP has signi cant intrinsic scatter. No other structural parameters like ellipticity or isophotal shape can reduce the scatter signi cantly. This is in contradiction to simple models, which predict that the presence of disks in E and S0 galaxies can introduce scatter in the FP. It remains unknown what the source of scatter is. It is therefore unknown whether this source produces systematic errors in distance determinations. The Mg 2 -relation for the cluster galaxies di ers slightly from cluster to cluster. Galaxies in clusters with lower velocity dispersions have systematically lower Mg 2 . The e ect can be caused by both age and metallicity variations. With the current stellar population models, it is in best agreement with our results regarding the FP if the o sets are mainly caused by di erences in metallicity. Most of the distances that we derive from the FP imply small peculiar motions (< 1000km s 1 ). The zero point of the FP must therefore be quite stable. Only for one cluster, located 28 from the direction towards the \Great Attractor", we nd a peculiar motion of 1300km s 1 . This motion is reduced to 890km s 1 if we use the FP corrected for the o set of the Mg 2 -relation. This con rms earlier suggestions that the residuals from the Mg 2 -relation can be used to ag galaxies with deviant populations, and possibly to correct the distance determinations for the deviations.

We have investigated the mass-metallicity (M-Z ) relation using galaxies at 0:4 < z < 1:0 from the Gemini Deep Deep Survey (GDDS) and Canada-France Redshift Survey (CFRS). Deep K-and z 0 -band photometry allowed us to measure stellar masses for 69 galaxies. From a subsample of 56 galaxies, for which metallicity of the interstellar medium is also measured, we identified a strong correlation between mass and metallicity for the first time in the distant universe. This was possible because of the larger baseline spanned by the sample in terms of metallicity (a factor of 7) and mass (a factor of 400) than in previous works. This correlation is much stronger and tighter than the luminosity-metallicity relation, confirming that stellar mass is a more meaningful physical parameter than luminosity. We find clear evidence for temporal evolution in the M-Z relation in the sense that at a given mass, a galaxy at z $ 0:7 tends to have lower metallicity than a local galaxy of similar mass. We use the z $ 0:1 Sloan Digital Sky Survey M-Z relation and a small sample of z $ 2:3 Lyman break galaxies with known mass and metallicity to propose an empirical redshift-dependent M-Z relation. According to this relation the stellar mass and metallicity in small galaxies evolve for a longer time than they do in massive galaxies. This relation predicts that the generally metal-poor damped Ly galaxies have stellar masses of the order of 10 8:8 M (with a dispersion of 0.7 dex) all the way from z $ 0:2 to 4. The observed redshift evolution of the M-Z relation can be reproduced remarkably well by a simple closed-box model in which the key assumption is an e-folding time for star formation that is higher or, in other words, a period of star formation that lasts longer in less massive galaxies than in more massive galaxies. Such a picture supports the downsizing scenario for galaxy formation.

ABSTRACT.Results of the commissioning of the first Gemini Multi-Object Spectrograph (GMOS) are described. GMOS and the Gemini-North telescope act as a complete system to exploit a large 8 m aperture with improved image quality. Key GMOS design features such as the on-instrument wave-front sensor (OIWFS) and active flexure compensation system maintain very high image quality and stability, allowing precision observations of many targets simultaneously while reducing the need for frequent recalibration and reacquisition of targets. In this paper, example observations in imaging, long-slit, and multiobject spectroscopic modes are presented and verified by comparison with data from the literature. The expected high throughput of GMOS is confirmed from standard star observations; it peaks at about 60% when imaging in the and bands, and at 45%-50% in r i spectroscopic mode at 6300 Å . Deep GMOS photometry in the , , and filters is compared to data from the g r i literature, and the uniformity of this photometry across the GMOS field is verified. The multiobject spectroscopic mode is demonstrated by observations of the galaxy cluster A383. Centering of objects in the multislit mask was achieved to an rms accuracy of 80 mas across the 5Ј .5 field, and an optimized setup procedure (now in regular use) improves this to better than 50 mas. Stability during these observations was high, as expected: the average shift between object and slit positions was 5.3 mas hr Ϫ1 , and the wavelength scale drifted by only 0.1 Å hr Ϫ1 (in a setup with spectral resolution of 6 Å ). Finally, the current status of GMOS on Gemini-North is summarized, and future plans are outlined.

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We examine the cosmic star formation rate (SFR) and its dependence on galaxy stellar mass over the redshift range using data from the Gemini Deep Deep Survey (GDDS). The SFR in the most massive galaxies 0.8 ! z ! 2 ( ) was 6 times higher at than it is today. It drops steeply from , reaching the present-. In contrast, the SFR density of intermediate-mass galaxies ( ) 10.2 10.8declines more slowly and may peak or plateau at . We use the characteristic growth time z ∼ 1.5 t { SFR to provide evidence of an associated transition in massive galaxies from a burst to a quiescent star r /r M SFR * formation mode at . Intermediate-mass systems transit from burst to quiescent mode at , while the z ∼ 2 z ∼ 1 lowest mass objects undergo bursts throughout our redshift range. Our results show unambiguously that the formation era for galaxies was extended and proceeded from high-to low-mass systems. The most massive galaxies formed most of their stars in the first ∼3 Gyr of cosmic history. Intermediate-mass objects continued to form their dominant stellar mass for an additional ∼2 Gyr, while the lowest mass systems have been forming over the whole cosmic epoch spanned by the GDDS. This view of galaxy formation clearly supports "downsizing" in the SFR where the most massive galaxies form first and galaxy formation proceeds from larger to smaller mass scales.