Astronomical instrumentation

Abstract:

The science case for the next generation of Extremely Large Telescopes (ELTs) covers a huge range of astronomical topics and requires a wide range of capabilities. Here we describe top-level requirements on an ELT, which were derived from some of the key science cases identified by European astronomers. After a brief summary of these science cases we discuss the requirements on the ELT system in terms of several parameters, including wavelength range, field of view, image quality etc. We discuss the science driver that sets the limits on each parameter. We also discuss specific requirements on instrumentation, site and adaptive optics. In several cases, detailed simulated observations will be required in order to set the requirements. While the example science cases provide a useful guide, we also note that an important goal is to develop a facility that covers a broad parameter space, and maintains flexibility in order to adapt to new scientific directions.

Abstract:

We present the fundamental plane (FP) in the z = 0.28 cluster of galaxies RX J0142.0+2131. There is no evidence for a difference in the slope of the FP when compared with the Coma Cluster, although the internal scatter is larger. On average, stellar populations in RX J0142.0+2131 have rest-frame V-band mass-to-light ratios (MILv) 0.29 ± 0.03 dex lower than in Coma. This is significantly lower than expected for a passively evolving cluster formed at zf = 2. Lenticular galaxies have lower average M/L v and a distribution of M/Lv with larger scatter than ellipticals. Lower mass-to-light ratios are not due to recent star formation: our previous spectroscopic observations of RX J0142.0+2131 E/S0 galaxies showed no evidence for significant star formation within the past ∼4 Gyr. However, cluster members have enhanced α-element abundance ratios, which may act to decrease M/Lv. The increased scatter in the RX J0142.0+2131 FP reflects a large scatter in M/Lv implying that galaxies have undergone bursts of star formation over a range of epochs. The seven easternmost cluster galaxies, including the second brightest member, have M/Lv consistent with passive evolution and zf = 2. We speculate that RX J0142.0+2131 is a cluster-cluster merger where the galaxies to the east are yet to fall into the main cluster body or have not experienced star formation as a result of the merger. © 2006. The American Astronomical Society. All rights reserved.

Abstract:

Observations and theoretical simulations have established a framework for galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark-matter haloes; mergers of haloes and galaxies then led to the hierarchical build-up of galaxy mass. It remains unclear, however, over what timescales galaxies were assembled and when and how bulges and disks - the primary components of present-day galaxies - were formed. It is also puzzling that the most massive galaxies were more abundant and were forming stars more rapidly at early epochs than expected from models. Here we report high-angular-resolution observations of a representative luminous star-forming galaxy when the Universe was only 20% of its current age. A large and massive rotating protodisk is channelling gas towards a growing central stellar bulge hosting an accreting massive black hole. The high surface densities of gas, the high rate of star formation and the moderately young stellar ages suggest rapid assembly, fragmentation and conversion to stars of an initially very gas-rich protodisk, with no obvious evidence for a major merger. © 2006 Nature Publishing Group.

Abstract:

The SAURON integral-field survey reveals that small (∼0.1,Re) kinematically decoupled cores (KDCs) in early-type galaxies are increasingly young toward the center and are typically found in fast-rotating galaxies, while large KDCs (∼0.5 Re) have homogeneously old stars and are present in non-rotating galaxies (McDermid et al. 2006). GALEX UV imaging further allows the direct identification of regions of recent star formation (0.5 Gyr). In NGC 2974 for example, young stars are identified in the center and an outer ring Jeong et al. 2006). Nuclear and inner ionised-gas rings (Sarzi et al. 2006) then suggest that current star formation is bar-driven. The CO detection rate of SAURON early-type galaxies is 40% (Combes et al. in prep.). Synthesis imaging reveals that it is generally contained in a well-ordered central disk, both in galaxies with a (young) central stellar disk (e.g. NGC 4459, NGC 4526) or a (young) KDC (e.g. NGC 3032, NGC 4150) (Young et al. in prep.). CO also traces well the young stellar populations and ionised gas distribution and kinematics, but in KDCs not always the stellar kinematics Emsellem et al. 2004; Sarzi et al. 2006; Kuntschner et al. 2006). © 2007 International Astronomical Union.