Dr Ian Lewis

Abstract:

We present the optical and mechanical design of the KMOS spectrograph module together with a detailed analysis of its performance. KMOS is a cryogenic near-infrared multi-object spectrograph being developed as a second-generation instrument for the VLT by a consortium of UK and German institutes. Three identical spectrograph modules provide Nyquist sampled spectra in the wavelength range covering the atmospheric bands z, J, H, and K with a resolving power exceeding 3200. The spectrographs are fully achromatic over the bands and the single mirror collimator and six-element camera, together with six high efficiency gratings provide high throughput. The optical performance analysis includes amongst others the spectral resolving power and variation of the PSF as a function of the pupil illumination.

Abstract:

We describe the build phase of the UK FMOS spectrograph, a 200 fibre cooled OH Suppression infrared spectrograph being constructed as part of Subaru's Fibre Multi Object Spectroscopy facility. Here we describe recent UK activities within the FMOS programme and the likely schedule for commissioning at Subaru.

Abstract:

The ROSAT-European Southern Observatory (ESO) flux-limited X-ray (REFLEX) galaxy cluster survey and the Two-degree Field Galaxy Redshift Survey (2dFGRS), respectively, comprise the largest, homogeneous X-ray selected cluster catalogue and completed galaxy redshift survey. In this work, we combine these two outstanding data sets in order to study the effect of the large-scale cluster environment, as traced by X-ray luminosity, on the properties of the cluster member galaxies. We measure the LX - σr relation from the correlated data set and find it to be consistent with recent results found in the literature. Using a sample of 19 clusters with LX ≥ 0.36 × 10⁴⁴ erg s^-1 in the 0.1-2.4 keV band, and 49 clusters with lower X-ray luminosity, we find that the fraction of early spectral type (η ≤ -1.4), passively evolving galaxies is significantly higher in the high-LX sample within A 200- We extend the investigation to include composite bj cluster luminosity functions, and find that the characteristic magnitude of the Schechter-function fit to the early-type luminosity function is fainter for the high-Lx sample compared to the low-Lx sample (ΔM* = 0.58 ± 0.14). This seems to be driven by a deficit of such galaxies with MbJ, ∼ -21. In contrast, we find no significant differences between the luminosity functions of star-forming, late-type galaxies. We believe these results are consistent with a scenario in which the high-LX clusters are more dynamically evolved systems than the low-LX clusters. © 2005 RAS.

Abstract:

We compare deep Magellan spectroscopy of 26 groups at 0.3 ≤ z ≤ 0.55, selected from the Canadian Network for Observational Cosmology 2 field survey, with a large sample of nearby groups from the 2PIGG catalogue. We find that the fraction of group galaxies with significant [O II]λ3727 emission (≥5 Å) increases strongly with redshift, from ∼29 per cent in 2dFGRS to ∼58 per cent in CNOC2, for all galaxies brighter than ∼M* + 1.75. This trend is parallel to the evolution of field galaxies, where the equivalent fraction of emission-line galaxies increases from ∼53 to ∼75 per cent. The fraction of emission-line galaxies in groups is lower than in the field, across the full redshift range, indicating that the history of star formation in groups is influenced by their environment. We show that the evolution required to explain the data is inconsistent with a quiescent model of galaxy evolution; instead, discrete events in which galaxies cease forming stars (truncation events) are required. We constrain the probability of truncation (P trunc) and find that a high value is required in a simple evolutionary scenario neglecting galaxy mergers (Ptrunc ≳ 0.3 Gyr-1). However, without assuming significant density evolution, Ptrunc is not required to be larger in groups than in the field, suggesting that the environmental dependence of star formation was embedded at redshifts z ≳ 0.45. © 2005 RAS.