Search

Detections and non-detections of Lyman alpha (Lyα) emission from z > 6 galaxies ( 7, where Lyα redshifts to near infra-red wavelengths. Here we present a search for z > 7.2 Lyα emission in 53 intrinsically faint Lyman Break Galaxy candidates, gravitationally lensed by massive galaxy clusters, in the KMOS Lens-Amplified Spectroscopic Survey (KLASS). With integration times of ∼7-10 h, we detect no Lyα emission with signal-to-noise ratio (S/N) > 5 in our sample. We determine our observations to be 80 per cent complete for 5σ spatially and spectrally unresolved emission lines with integrated line flux >5.7 × 10−18 erg s−1 cm−2. We define a photometrically selected sub-sample of 29 targets at z = 7.9 ± 0.6, with a median 5σ Lyα EW limit of 58 Å. We perform a Bayesian inference of the average intergalactic medium (IGM) neutral hydrogen fraction using their spectra. Our inference accounts for the wavelength sensitivity and incomplete redshift coverage of our observations, and the photometric redshift probability distribution of each target. These observations, combined with samples from the literature, enable us to place a lower limit on the average IGM neutral hydrogen fraction of > 0.76 (68 per cent), > 0.46 (95 per cent) at z ∼ 8, providing further evidence of rapid reionization at z ∼ 6-8. We show that this is consistent with reionization history models extending the galaxy luminosity function to MUV −12, with low ionizing photon escape fractions, fesc 15 per cent.

Exploiting the data of the Grism Lens-Amplified Survey from Space (GLASS), we characterize the spatial distribution of star formation in 76 highly active star-forming galaxies in 10 clusters at 0.3 < z < 0.7. All of these galaxies are likely restricted to first infall. In a companion paper, we contrast the properties of field and cluster galaxies, whereas here we correlate the properties of H? emitters to a number of tracers of the cluster environment to investigate its role in driving galaxy transformations. H? emitters are found in the clusters out to 0.5 virial radii, the maximum radius covered by GLASS. The peak of the H? emission is offset with respect to the peak of the UV continuum. We decompose these offsets into a radial and a tangential component. The radial component points away from the cluster center in 60% of the cases, with 95% confidence. The decompositions agree with cosmological simulations; that is, the H? emission offset correlates with galaxy velocity and ram-pressure stripping signatures. Trends between H? emitter properties and surface mass density distributions and X-ray emissions emerge only for unrelaxed clusters. The lack of strong correlations with the global environment does not allow us to identify a unique environmental effect originating from the cluster center. In contrast, correlations between H? morphology and local number density emerge. We conclude that local effects, uncorrelated to the cluster-centric radius, play a more important role in shaping galaxy properties.

Exploiting the slitless spectroscopy taken as part of the Grism Lens-Amplified Survey from Space (GLASS), we present an extended analysis of the spatial distribution of star formation in 76 galaxies in 10 clusters at 0.3 < z < 0.7. We use 85 foreground and background galaxies in the same redshift range as a field sample. The samples are well matched in stellar mass (108-1011 M⊙) and star formation rate (0.5-50 M⊙ yr-1). We visually classify galaxies in terms of broad band morphology, H? morphology, and likely physical process acting on the galaxy. Most H? emitters have a spiral morphology (41% ± 8% in clusters, 51% ± 8% in the field), followed by mergers/interactions (28% ± 8%, 31% ±7%, respectively) and early-type galaxies (remarkably as high as 29% ±8% in clusters and 15% ± 6% in the field). A diversity of H? morphologies is detected, suggesting a diversity of physical processes. In clusters, 30% ± 8% of the galaxies present a regular morphology, mostly consistent with star formation diffused uniformly across the stellar population (mostly in the disk component, when present). The second most common morphology (28% ±8%) is asymmetric/jellyfish, consistent with rampressure stripping or other non-gravitational processes in 18% ± 8% of the cases. Ram-pressure stripping appears significantly less prominent in the field (2% ± 2%), where the most common morphology/mechanism appears to be consistent with minor gas-rich mergers or clump accretion. This work demonstrates that while environmentspecific mechanisms affect galaxy evolution at this redshift, they are diverse and their effects are subtle. A full understanding of this complexity requires larger samples and detailed and spatially resolved physical models.

We present the first study of the spatial distribution of star formation in zsim;.5 cluster galaxies. The analysis is based on data taken with the Wide Field Camera 3 as part of the Grism Lens-Amplified Survey from Space (GLASS). We illustrate the methodology by focusing on two clusters (MACS 0717.5+3745 and MACS 1423.8+2404) with different morphologies (one relaxed and one merging) and use foreground and background galaxies as a field control sample. The cluster+field sample consists of 42 galaxies with stellar masses in the range 108-1011 Moand star formation rates in the range 1-20 Mo yr-1. Both in clusters and in the field, Hα is more extended than the rest-frame UV continuum in 60% of the cases, consistent with diffuse star formation and inside-out growth. In ∼20% of the cases, the Hα emission appears more extended in cluster galaxies than in the field, pointing perhaps to ionized gas being stripped and/or star formation being enhanced at large radii. The peak of the Hα emission and that of the continuum are offset by less than 1 kpc. We investigate trends with the hot gas density as traced by the X-ray emission, and with the surface mass density as inferred from gravitational lens models, and find no conclusive results. The diversity of morphologies and sizes observed in Hα illustrates the complexity of the environmental processes that regulate star formation. Upcoming analysis of the full GLASS data set will increase our sample size by almost an order of magnitude, verifying and strengthening the inference from this initial data set.