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

August 1997 • 1997MNRAS.289..621A

Authors • Armus, L. • Neugebauer, G. • Lehnert, M. D. • Matthews, K.

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<K<20.2 mag at radii of 1.7<Deltar<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 Mg ii 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 at z>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 Lyalpha 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 in J-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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Lee Armus

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