To extend the molecular gas measurements to typical L* star-forming galaxies (SFGs) at z ∼ 1.5 − 3, we have observed CO emission for five strongly-lensed galaxies selected from the Herschel Lensing Survey. The combined sample of our L* SFGs with CO-detected SFGs at z >1 from the literature shows a large spread in star formation efficiency (SFE). We find that this spread in SFE is due to variations of several physical parameters, primarily the specific star formation rate, but also stellar mass and redshift. An increase of the molecular gas fraction (fgas) is observed from z ∼ 0.2 to z ∼ 1.2, followed by a quasi non-evolution toward higher redshifts, as found in earlier studies. We provide the first measure of fgas of z >1 SFGs at the low-stellar mass end between 109.4 < M∗/M⊙ < 109.9, which shows a clear fgas upturn.

We present the results obtained from our deep survey of lensing clusters aimed at constraining the abundance of star-forming galaxies at z∼6–11.

Recent progress in measuring the optical depth of neutral hydrogen in distant quasars and that of electron scattering of microwave background photons suggests that most of the sources responsible for cosmic re-ionisation probably lie in the redshift interval 6 to 10. We present two new observational results which, together, provide valuable constraints on the contribution from star-forming sources in this redshift interval. First, using a large sample of v-band dropouts with unconfused Spitzer-IRAC detections, we determine the integrated stellar mass density at z = 5. This provides a valuable ‘integral constraint’ on past star formation. It seems difficult to reconcile the observed stellar mass at z = 5 with the low abundance of luminous i-z- and J-band dropouts in deep Hubble Space Telescope data. Accordingly, we explore whether less luminous star-forming sources in the redshift interval 6 to 10 might be the dominant cause of cosmic re-ionization. In the second component of our research, we report on the results of two surveys for weak Lymanα emitters and z- and J-band dropouts highly-magnified by foreground lensing clusters. Although some promising z = 8–9 candidates are found, it seems unlikely that low luminosity sources in this redshift interval can dominate cosmic reionization. If our work is substantiated by more extensive and precise surveys, the bulk of the re-ionizing photons may come from yet earlier sources lying at redshifts z>10.

We describe an observation designed to find Hα emission from galaxies at z≃7–12 made using the InfraRed spectrograph (IRS) on the Spitzer Space Telescope.

We report the results obtained from VLT-isaac near-IR spectroscopy of two low-luminosity z ≃ 1.9 galaxies located in the core of the lensing cluster AC 114. The amplification factor allowed to obtain, for the first time, physical properties (SFR, abundance ratios, mass, etc.) of star-forming galaxies, 1 - 2 mag fainter than in previous studies of LBGs at z ≈ 3.

We expand on the work of Brainerd, Blandford & Smail (1996) (BBS), using a larger archival WFPC-2 dataset including many galaxy redshifts. It is clear from our data that the ellipticity distribution of images changes substantially with observed magnitude (figure 1, left) which is shown by simulations to be mainly the result of detection effects. We have detected a lensing signal, using a similar selection method to BBS and are also implementing a maximum likelihood method to constrain halo parameters. Using simulations, we show in figure 1 (right) that the signal is consistant with typical halo velocity dispersions of σ∗ ∼ 70–100 kms−1 However, the radial extent of the halos is less well constrained.

We discuss HST imaging of eight spectroscopically-confirmed giant arcs, pairs and arclets. Although our HST observations include both pre- and post-refurbishment images, the depth of the exposures guarantees that the majority of the arcs are detected with diffraction-limited resolution. We present the size information on these distant field galaxies in the light of HST studies of lower redshift samples. We suggest that the dominant population of star-forming galaxies at z ∼ 1 is a factor of 1.5–2 times smaller in size than the equivalent population in the local field. This implies either a considerable evolution in the sizes of star-forming galaxies within the last ∼10 Gyrs or a shift in the relative space densities of massive and dwarf star-forming systems over the same time scale.

Weak shear maps of the outer regions of clusters have been successfully used to map the distribution of mass at large radii. The effects of substructure in clusters on such reconstructions of the total mass have not been systematically studied. We propose a new method to study the effect of perturbers (bright cluster galaxies or sub-groups within the cluster) on the weak shear field. We present some analytic results below.