THE UNUSUAL NEAR-INFRARED MORPHOLOGY OF THE RADIO-LOUD QUASAR 4C+09.17

Near-infrared images of the luminous, high-redshift (z=2.1108), radio- loud quasar 4C + 09.17 reveal a complex structure. The quasar (K=15.76 mag) is surrounded by three 'companion' objects having 17.9 < K < 20. 2 mag at radii of 1.7 < Delta r < 2.9 arcsec, as well as bright, diffu se emission. The brightest companion has a redshift of z = 0.8384 (Leh nert & Becker), and its optical-infrared colours (Lehnert et al.) are consistent with a late-type spiral galaxy at this redshift with a lumi nosity of about 2L(). This object is probably the galaxy responsible for the strongest MgII absorption-line system seen in the spectrum of 4C + 09.17 by Barthel et al. Redshifts are not available for the remai ning two companions. The red colours of the second brightest companion appear most consistent with a high-redshift star-forming galaxy at z > 1.5. If this object is at the redshift of 4C + 09.17, it has a lumin osity of about 7L(). The faintest companion has colours which are unl ike those expected from either a spiral or an E/SO galaxy at any redsh ift associated with the 4C + 09.17 system. Since this object lies alon g the same direction as the radio jet/lobe of 4C + 09.17, as well as t he extended Ly alpha emission mapped by Heckman et al., we suggest tha t this component can be explained as a combination of strong line emis sion and scattered QSO light. The resolved, diffuse emission surroundi ng 4C + 09.17 is bright, K similar to 17.0 mag, and about 1 mag redder in J - K than the quasar. If this emission is starlight, a very lumin ous elliptical host galaxy is implied for 4C + 09.17. Scattered and re ddened AGN light, emission-line gas, and flux from absorbing galaxies along the line of sight may all contribute to this emission.