The unusual near-infrared morphology of the radio-loud quasar 4C + 09.17

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Abstract
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 r< 2.9 arcsec, as well as bright, diffuse emission. The brightest companion has a redshift of z = 0.8384 (Lehnert & Becker), and its optical-infrared colours (Lehnert et al.) are consistent with a late-type spiral galaxy at this redshift with a luminosity 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 remaining two companions. The red colours of the second brightest companion appear most consistent with a high-redshift star-forming galaxy atz > 1.5. If this object is at the redshift of 4C + 09.17, it has a luminosity of about 7L⋆. The faintest companion has colours which are unlike those expected from either a spiral or an E/S0 galaxy at any redshift associated with the 4C +09.17 system. Since this object lies along the same direction as the radio jet/lobe of 4C + 09.17, as well as the extended Lyα emission mapped by Heckman et al., we suggest that this component can be explained as a combination of strong line emission and scattered QSO light. The resolved, diffuse emission surrounding 4C + 09.17 is bright, K~ 17.0 mag, and about 1 mag redder inJ—K than the quasar. If this emission is starlight, a very luminous elliptical host galaxy is implied for 4C +09.17. Scattered and reddened AGN light, emission-line gas, and flux from absorbing galaxies along the line of sight may all contribute to this emission.
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