GMOS SV program 63

Only rarely does observational astronomy discover genuinely new classes of object. In extragalactic astronomy, the most striking recent discovery has been that by Steidel et al (2000) of Giant Lyman Alpha Nebulae --- high-redshift gaseous nebulae extended over >100 kpc scales, and associated with intense submillimetre dust emission (Chapman et al. 2001). The origin of these nebulae is as yet mysterious, although they are very reminiscent of the Ly-alpha nebulae surrounding distant powerful radiogalaxies.

Observations of distant radio galaxies have shown that the properties of their haloes are strongly influenced by interactions between the powerful radio jets and the ambient medium. This makes it very tricky to make basic kinematical studies: e.g. those aimed at determining whether these haloes are rotating (which would allow dynamical measurements of the system masses); or, those aimed at mapping outflows (which would allow measurement of the timescale over which the driving force, e.g. a superwind, has been in operation). It also makes them difficult targets for studies of HI absorption by the halo since neutral hydrogen appears to be ionized by radiosource-induced shocks. There are hints, however, from the weak emission at the outer edges of radio galaxy haloes (e.g. van Ojik et al, 1996) that similar measurements would provide clean results concerning the kinematics and composition of any similar nebula associated with a radio-quiet object. Steidel et al.'s discovery of radio-quiet Ly-alpha nebulae, together with the development of IFU systems on 8-m class telescopes, means that both kinematical and absorption studies can now be pursued throughout the nebula at good signal-to-noise ratio. Since these haloes look likely to be associated with the formation of galaxies within protocluster cores, understanding their kinematics and composition is vital for our understanding of how massive galaxies form, and of the feedback mechanisms that link the formation of galaxy spheroids and their associated supermassive black holes (e.g. Silk & Rees 1998).

Only two of these haloes are currently known, and we proposed Gemini SV observations of the brightest of these (in Ly-alpha), which is also recently been associated with an intense source of submillimetre emission. Spectral resolution (just) better than 200 km/s is adequate to map out the velocity field in the nebula (differences in velocity are seen on the scale of 2000 km/s over a few arcsec in these objects; Steidel et al. 2000). By mosaicing two IFU positions, we can map out the kinematics and HI absorption over the full nebula. Since the diffuse nebula will be invisible in continuum light, this will provide a vital test of strategies for acquiring narrow-line-light dominated targets. The central part of the nebula will be detected in both pointings, allowing valuable checks of techniques for mosaicing IFU fields.

References:
Chapman et al. (2001), astro-ph/0010101
Silk & Rees (1998), A&A, 331, L1
Steidel et al. (2000), ApJ, 532, 170
van Ojik et al (1996), A&A, 313, 25