Optical Spectroscopy of Candidate Hot Spots in Radio Galaxies and Quasars

Keel, W.C. and Martini, P. 1995, AJ, 109, 2305

We present low-dispersion spectrophotometry (0.5 - 1.0 um) for several objects previously identified as candidates for optical emission from hot spots in radio galaxies and quasars. Detailed spectral fits were used to discriminate between power-law continua and other types of spectra, including associated galaxies and foreground stars. Of the objects observed, the 3C 319 "hot spot" proves to be a galaxy in the associated cluster, and the most prominent candidate for the 3C 390.3 hot spot is a foreground K star. We confirm that the spectrum of the 3C 247 hot spot is best-fit by a power-law form, and together with published K-Band data, find evidence of a turnover in the synchrotron spectrum at about 1.2 \times 10^14 Hz. The pure continuum nature of the 3C 303 hot spot is confirmed; in fact, in none of the hot spots observed do we detect line emission. Our data for the hot spot near PKS 2135-147 are well represented by a power-law continuum, but other evidence indicates that this is another galaxy superposition (in which the strongest spectral features fall outside our observed range).

We meaure the spectral shape of the 3C 273 jet in three regions, the outermost of which includes the radio hot spot at the end of the jet. This outer region has a much steeper spectrum (\alpha = -4.5) than the brightest part of the jet (\alpha = -1.0) breaking any pattern of higher cutoff or turnover frequencies in hot spots compared to optically-detected jets.

We discuss briefly some aspects of the nuclear spectra of the radio galaxies in the sample. Of particlar note is the simultaneous measurement of the emission lines from [O II] \lambda 3727 to H\alpha in 3C 330 at z = 0.55.

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