Jet-triggered star formation in young radio galaxies

Abstract

Emission in the ultraviolet continuum is a salient signature of the hot, massive, and consequently short-lived, stellar population that traces recent or ongoing star formation. With the aim of mapping star forming regions and morphologically separating the generic star formation from that associated with the galaxy-scale jet activity, we obtained high-resolution ultraviolet (UV) imaging from the Hubble Space Telescope for a sample of nine compact radio sources. Out of these, seven are known Compact Steep Spectrum (CSS) galaxies that host young, kiloparsec-scale radio sources and hence are the best candidates for studying radio-mode feedback on galaxy scales, while the other two form a control sample of larger sources. Extended UV emission regions are observed in six of the seven CSS sources showing close spatial alignment with the radio-jet orientation. If other mechanisms possibly contributing to the observed UV emission are ruled out, this could be evidence in support of jet-triggered star formation in the CSS phase of radio galaxy evolution and in turn of the “positive feedback” paradigm of host–active galactic nuclei interaction.