Galaxy formation and evolution

Abstract:

The current and forthcoming observations of large samples of high-redshift galaxies selected according to various photometric and spectroscopic criteria can be interpreted in the context of galaxy formation, by means of models of evolving spectral energy distributions (SEDs). We hereafter present STARDUST which gives synthetic SEDs from the far UV to the submm wavelength range. These SEDs are designed to be implemented into semi-analytic models of galaxy formation.

Abstract:

We review the results of a major spectroscopic survey of nearby Starbursts and moderate redshift Ultraluminous IRAS Galaxies (ULIRGs) using ISO-SWS, ISOPHOT-S and ISOCAM (CVF) on board ISO. Detailed modeling reveals that massive stars, M-upper greater than or equal to 100 M-. are formed in most Starbursts in relatively short bursts (one or a few O star lifetimes). In the area of ULIRGs we address the main question of the dominant energy source as well as their evolution. We have found that the combination of mid-infrared fine structure line ratio with the strength of the PAH feature provides an excellent tool for discriminating between starburst and AGN activity. Our studies indicate that, on average, ULIRGs are mainly powered by Starbursts. The strength of the PAH feature is also used to probe for evolutionary effects. We find no evidence that ULIRGs found in advanced stages of merging are more AGN-like, as postulated by the classical evolutionary scenario. We suggest that local conditions (related to the energetics of the AGN) determine the dominance of the starburst or AGN.

Abstract:

We have obtained ISOPHOT-S low resolution mid-infrared spectra of a sample of 60 Ultraluminous Infrared Galaxies (ULIRGs). We use the strength of the 'PAH' mid-infrared features as a discriminator between starburst and AGN activity, and to probe for evolutionary effects. Observed ratios of PAH features in ULIRGs differ slightly from those in lower luminosity starbursts. We suggest that such PAH ratio changes relate to the conditions in the interstellar medium in these galaxies, and in particular to extinction. (C)1999 COSPAR. Published by Elsevier Science Ltd.

Abstract:

As the only two optical instruments appearing in its first fleet of instrumentation, the GEMINI MultiObject Spectrograph (GMOS) are indeed being developed as workhorse instruments. One GMOS will be located at each of the GEMINI telescopes to perform: a) exquisite direct imaging, b) 5.5 arcminute longslit spectroscopy, c) up to 600 object multislit spectroscopy, and d) about 2000 element integral field spectroscopy. The GMOSs are the only GEMINI instrumentation duplicated at both telescopes. The UK and Canadian GMOS team successfully completed their critical design review in February 1997. They are now well into the fabrication phase, and will soon approach integration of the first instrument. The first GMOS is scheduled to be delivered to Mauna Kea in the fall of'99 and the second to Cerro Pachon one year later. In this paper, we will look at how a few of the more interesting details of the final GMOS design help meet its demanding scientific requirements. These include its transmissive optical design and mask handling mechanisms. We will also discuss our plans for the mask handling process in GEMINI'S queue scheduled environment, from the taking of direct images through to the use of masks on the telescope. Finally, we present the status of fabrication and integration work to date.