SPATIALLY RESOLVED OPTICAL-IMAGES OF HIGH-REDSHIFT QUASI-STELLAR OBJECTS

We present and discuss the results of a program of deep optical imaging of 19 high-redshift (z greater-than-or-equal-to 2) radio-loud QSOs. These data represent the first large body of nonradio detections of spatially resolved structure surrounding high-redshift QSOs. In 15 of 18 cases, the Ly-alpha emission is spatially resolved, with a typical size of 100 kpc (for H0 = 75 km s-1 Mpc-1; q0 = 0). The luminosity of the resolved Ly-alpha is almost-equal-to 10(44) ergs s-1 (almost-equal-to 10% of the total Ly-alpha luminosity). The nebulae are usually asymmetric and/or elongated with a morphological axis that aligns with the radio source axis to better than almost-equal-to 30-degrees. These properties are quite similar to those of the Ly-alpha nebulae associated with high-z radio galaxies. The brighter side of the nebula is generally on the same side as the brighter radio emission and/or one-sided, jetlike radio structure. There is no strong correlation between the Ly-alpha isophotal and radio sizes (the Ly-alpha nebulae range from several times larger than the radio source to several times smaller). None of the properties of the nebulae correlate with the presence or strength of C IV "associated" absorption (Z(abs) almost-equal-to Z(em)). It is likely that the nebulae are the interstellar or circumgalactic medium of young or even protogalaxies being photoionized by QSO radiation that escapes anisotropically along the radio axis. Photoionization equilibrium arguments imply that the Ly-alpha emission arises in small (parsec-scale) dense (10(2)-10(3) cm-3) clouds. If the clouds are not confined, their short lifetime to photoevaporation requires a total reservoir of a few times 10(11) M. in dense gas. If the clouds are confined by a hot, diffuse intercloud medium at the Compton or Virial temperature (almost-equal-to 10(7) K), the mass of this ICM is almost-equal-to 10(12) M.. Cloud confinement by a "cocoon" inflated by the radio source or by a thermal QSO wind also entail a substantial total gas mass (> 10(11) M.). The interaction of the radio jet with the ambient gaseous medium may enhance the (radio) visibility of the jet plasma, and lead directly to the small sizes and distorted and asymmetric structures of the radio sources. Indeed, the gas pressures inferred for the Ly-alpha nebulae are far larger than those inferred around low-z radio galaxies and radio-loud QSOs. For at least six and probably 10 of the QSOs, the UV continuum is also spatially resolved, with diameters of 40-80 kpc. The spatially resolved material is typically almost-equal-to 10% as bright as the QSO, with an average UV luminosity (lambda-P-lambda at almost-equal-to 1200 angstrom) of almost-equal-to 2 x 10(45) ergs s-1 (comparable to the UV luminosities of high-z radio galaxies). The morphological axes of the spatially extended continuum structures do not generally align with either the radio or Ly-alpha morphological axes (contrary to the properties of high-z radio galaxies). This UV "fuzz" may be starlight from the QSO host galaxy, scattered QSO light, or even a foreground galaxy acting as a gravitational lens. By analogy to high-z radio galaxies, the first possibility is most likely, implying typical star-formation rates of several hundred M. per year. If sustained for a galaxy dynamical time (several times 10(8) yr) this would result in the formation of a galaxy's worth of stars. High-redshift radio-loud QSOs may be associated with the formation of some galaxies. Finally, we note that several QSOs have possible close (within 100 kpc of the QSO) companion galaxies with Ly-alpha emission. These require spectroscopic confirmation.