A novel concept for a very efficient tunable filter for the optical and near infrared is proposed. The filter consists of two parallel volume phase holographic Bragg gratings used in a dispersion-recombination configuration. The passband profile is determined by the first order grating efficiency curve which changes in wavelength according to the angle of incidence. The filter can be continuously tuned over ranges of wavelengths larger than 600 nm by adjusting the tilt of the gratings, while bandwidth can be selected between 0.1 and 200 nm. The conceptual design is presented, along with predicted performances. Potentially useful instruments for large volume surveys
and targeted observations are explored, along with application in areas other than astronomy.
High redshift radio galaxies are great cosmological tools for pinpointing the most massive objects in the early Universe: massive forming galaxies, active super-massive black holes and proto-clusters. We report on deep narrow-band imaging and spectroscopic observations of several z > 2 radio galaxy fields to investigate the nature of giant Ly-α nebulae centered on the galaxies and to search for over-dense regions around them. We discuss the possible implications for our understanding of the formation and evolution of massive galaxies and galaxy clusters.
The host galaxies of powerful radio sources are ideal laboratories to study active galactic nuclei (AGN). The galaxies themselves are among the most massive systems in the universe, and are believed to harbor supermassive black holes (SMBH). If large galaxies are formed in a hierarchical way by multiple merger events, radio galaxies at low redshift represent the end-products of this process. However, it is not clear why some of these massive ellipticals have associated radio emission, while others do not. Both are thought to contain SMBHs, with masses proportional to the total luminous mass in the bulge. It either implies every SMBH has recurrent radio-loud phases, and the radio-quiet galaxies happen to be in the "low" state, or that the radio galaxy nuclei are physically different from radio-quiet ones, i.e. by having a more massive SMBH for a given bulge mass.
Here we present the first results from our adaptive optics imaging and spectroscopy pilot program on three nearby powerful radio galaxies. Initiating a larger, more systematic AO survey of radio galaxies (preferentially with Laser Guide Star equipped AO systems) has the potential of furthering our understanding of the physical properties of radio sources, their triggering, and their subsequent evolution.
At low redshifts powerful radio sources are uniquely associated with massive galaxies, and are thought to be powered by supermassive black holes. Modern 8m-10m telescopes may be used to find their likely progentors at very high redshifts to study their formation and evolution.
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