While at low redshift the kinematics of the extended gas in radio galaxies is generally explained in terms of gravitational motions, the mechanism responsible for the extreme motions at higher redshifts is not well understood. The apparent connection between the size of the radio source and the emission line kinematics observed at (van Ojik et al. 1997) suggests interactions between the radio and optical structures that perturb the kinematics. This is supported by the discovery in some HzRG of haloes of ionized gas extending beyond the radio structures that emit narrow Ly ( km s-1) compared to the inner regions ( km s-1) (van Ojik et al. 1996).
Baum & McCarthy (2000) studied a much larger sample covering a wider range in redshift. They find no (or very weak) correlation between the emission line kinematics and the ratio of the radio to nebular size. The authors support a gravitational origin for the kinematics of HzRG. Bipolar outflows (possible consequence of a circumnuclear starburst) have also been proposed by some authors (e.g. Chambers 1998; Taniguchi & Shioya 2000).
Understanding the nature of the kinematics in HzRG will help to answer some open questions related to these galaxies:
To date, the kinematic studies of the gas in HzRG have been done in the optical. The main limitation has been the need for a large collecting area to detect the emission lines with high signal/noise ratio (S/N) in the extended gas. With 3-4 m telescopes, only [OII]3727 (z<1.2) or Ly () could be used. At () the uncertainties are important, since Ly is highly sensitive to dust/neutral gas absorption. The strong optical (rest frame) emission lines ([OIII]5007, 4959, [OII]3727) are more reliable. However, they are redshifted into the NIR and the need for a large collecting area has constrained the NIR spectroscopic studies of HzRG (and quasars) to the spatially integrated properties (e.g. Jackson & Rawlings 1997; McIntosh et al. 1999; Larkin et al. 2000)
This is the epoch of the 8-10 m telescope generation. We are in the position for the first time to study the kinematics of the extended gas in HzRG:
In spite of the opportunities opened by the new technological facilities, the study of the kinematic properties of HzRG is still complex. The goal of this paper is to assess the main sources of uncertainty and provide solutions to solve them.
|Figure 1: KeckII+LRISp spectra of the HzRG B3 0731+438 (z=2.42). The new generation of 8-10 m telescopes allows for the first time the detection of emission lines other than Ly in the extended gas of very distant radio galaxies () with high S/N|
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