Polarized light in high-redshift radio galaxies
HIGH-redshift radio galaxies are characterized by ultraviolet excesses1,2 associated with elongated continuum and emission-line structures aligned along their radio axes3,4. Commonly, these properties are interpreted in terms of jet-induced star formation. However, observations of a blue, polarized continuum knot in the low-redshift radio galaxy PKS2152 — 69 have suggested an alternative beaming/scattering model5,6. To test this model we have obtained imaging-polarimetry observations of two high-redshift radio galaxies: 3C277.2 (z = 0.766) and 3C368 (z = 1.132). We find that both sources are strongly linearly polarized at ultraviolet rest wavelengths, with E-vectors within 25° of perpendicular to the axis of the extended continuum and radio structures. This implies that a large proportion of the ultraviolet light in these objects does not come directly from stars and we suggest it is scattered radiation from the nucleus. These observations also have important implications for beaming models of the active nuclei and for our understanding of the evolution of the host galaxies.
Minkowski's object - a starburst triggered by a radio jet
New radio and optical images of Minkowski's object, a peculiar blue object near the elliptical galaxy NGC 541 in the cluster Abell 194, are presented. The observations show that the object is a region with bright optical line and continuum emission which are morphologically related and associated with a radio jet emanating from NGC 541. Optical emission is brightest near the edges of the jet, correlated with the absence of polarized radio emission, and filamentary downstream where the radio jet is deflected and decollimated. Minkowski's object exhibits unusually bright optical continuum emission, and its spectrum resembles those of galaxies dominated by giant H II regions. Observations of the prototypical starburst galaxy NGC 7714 (Weedman et al., 1981) confirm that the optical emission from Minkowski's object is caused by the photoionization of gas by type O and B stars. 71 references.
Conserved Quantities of a Class of Nonlinear Difference-Difference Equations
Higher-order conserved quantities of a class of nonlinear difference-difference equations which are related to the discrete-time Toda equation are obtained using the Miura transformations.