THE OPTICAL CUTOFF SOURCE-0500- A BACKGROUND QUASAR SEEN THROUGH A FOREGROUND GALAXY(019 )

The optical spectrum of the extremely red (alpha(R-B) approximate to - 7) optical counterpart of the radio source 0500+019 shows an unidentif ied emission line at 6543 Angstrom in addition to absorption and emiss ion lines of Ca H&K lambda lambda 3933,3968, [O II] lambda 3727, and [ O III] lambda lambda 4959,5007 at a redshift of z = 0.583. The optical (R-band) morphology of 0500+019 consists of an asymmetric galaxy with no obvious point source. In contrast, the infrared (K-s) morphology i s dominated by a point source, while the galaxy component seen in the R-band is clearly visible only after image restoration. Since the emis sion line at 6543 Angstrom cannot be identified within the z = 0.583 r edshift system, it is interpreted as being due to a second system of c urrently unknown redshift. The optical and infrared morphologies then naturally lead to a picture, where a background source, likely a quasa r seen in the infrared, is located behind a foreground galaxy, which i s most clearly detected in the optical. In this case the steep optical spectral index may be the result of foreground absorption rather than being a source intrinsinc property.