Techniques in high resolution observations from the ground and space, and imaging of the merging environments of radio galaxies at redshift 1 to 4




Steinbring, Eric

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High resolution imaging and spectroscopy are invaluable tools for extragalactic astronomy. Galaxies with redshifts of 1 or more subtend a very small angle on the sky—typically, only about an arcsecond. Unfortunately, this is also approximately the angular resolution achieved with a ground-based telescope regardless of its aperture. Atmospheric turbulence ruins the image before it reaches the telescope but the emerging technology of adaptive optics (AO) gives the observer the possibility, within limitations, of correcting for these effects. This is the case for instruments such as the Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) and the Gemini North Telescope (Gemini) Altitude-Conjugate Adaptive Optics for the Infrared (Altair) systems. The alternative is to rise above the limitations of the atmosphere entirely and put the telescope in space, for example, the Hubble Space Telescope (HST) and its successor, the Next-Generation Space Telescope (NGST). I discuss several techniques that help overcome the limitations of AO observations with existing instruments in order to make them more comparable to imaging from space. For example, effective dithering and flat-fielding techniques as well as methods to determine the effect of the instrument on the image of, say, a galaxy. The implementation of these techniques as a software package called AOTOOLS is discussed. I also discuss computer simulations of AO systems, notably the Gemini Altair instrument, in order to understand and improve them. I apply my AO image processing techniques to observations of high-redshift radio galaxies (HzRGS) with the CFHT AOB and report on deep imaging in near-infrared (NIR) bands of 6 HzRGs in the redshift range 1.1 ≤ z ≤ 3.8. The NIR is probing the restframe visible light—mature stellar populations—at these redshifts. The radio galaxy is resolved in all of these observations and its ‘clumpier’ appearance at higher redshift leads to the main result—although the sample is very small—that these galaxy environments are undergoing mergers at high redshift. Finally, I look to the future of high resolution observations and discuss simulations of imaging and spectroscopy with the NGST. The computer software NGST VI/MOS is a ‘virtual reality’ simulator of the NGST observatory providing the user with the opportunity to test real observing campaigns.



Optics, Adaptive, High resolution spectroscopy, Large astronomical telescopes