A model to explain the correlation between the optical and radio properties of high-redshift galaxies

Recent observations indicate that steep-spectrum radio sources are often galaxies at high redshift which have optical and near-infrared continuum emission originating from a region which is elongated, and the axis of this elongation is the same as that defined by the radio lobes, as discussed by Chambers et al. and McCarthy et al. Such a correlation between the optical and radio axes could arise if the optical and infrared emission were the end result of the action of jets tunneling through the ambient gas associated with the galaxy/protogalaxy. As detailed here, the action of jets tunneling through an ambient medium leads to two coupled shock systems: a driven shock wave along the jet axis and a blast wave perpendicular to the jet axis. Hence, the action of jets tunneling through the ambient protogalactic medium sends a shock wave perpendicular to the radio jet axis; this not only shock heats the ambient gas, but it also, under appropriate conditions, triggers star formation. The optical and infrared emission could arise from the stars and/or from the shock-heated gas, and because the envelope of the blast wave is elongated along the axis defined by the jets, the optical emission will arise from a region whose elongation axis is the same as that of the jets. The radio emission arises from the radio lobes which are inferred to be the termination regions of the jets, where the action of the jet tunneling through the ambient medium is taking place. Such a model for the "alignment effect" leads to several consequences. The power being channeled into the jets, the relative extent of the emitting regions, the conditions necessary for star formation to occur, the relation between the spatial extent of the red and blue continuum components and the emission-line region, how long the alignment will persist, the implications for the epochs of galaxy formation, and the implications for the immediate environment of these galaxies are discussed.