An Extremely Red Nucleus in an Absorbed QSO at z=0.65

The results of $$ K$$-band-imaging observations of a candidate of an absorbed QSO at $$ z=0.653$$, AX J131831+3341, are presented. The $$ B-K$$ color of the object is 4.85 mag, which is much redder than optically-selected QSOs. The $$ K$$-band image shows nuclear and extended components, the same as in the optical $$ V$$-, $$ R$$-, and $$ I$$-band images. The nuclear component ($$ I-K = 4.29$$ mag) is much redder than the power-law models with energy indices of 0 to $$-1.0$$, which well reproduce the $$ V-R$$ and $$ R-I$$ optical colors of the nuclear component. A heavily absorbed ($$ A_V \sim 3$$ mag) nucleus may emerge in the $$ K$$-band, while optical light may originate from scattered nuclear light. The $$ I-K$$ color of the extended component is 2.2 mag, which is consistent with the post-starburst nature of the host galaxy, which is also suggested from the $$ V-R$$ and $$ R-I$$ colors of the extended component.