Minkowski’s Object: A Starburst Triggered by a Radio Jet, Revisited

Abstract

We present neutral hydrogen, ultraviolet, optical, and near-infrared imaging, and optical spectroscopy, of Minkowski's Object (MO), a star-forming peculiar galaxy near NGC 541. The observations strengthen evidence that star formation in MO was triggered by the radio jet from NGC 541. Key new results are the discovery of a 4.9 × 10^8 M_⊙ double H I cloud straddling the radio jet downstream from MO, where the jet changes direction and decollimates; strong detections of MO, also showing double structure, in UV and Hα; and numerous H II regions and associated clusters in MO. In UV, MO resembles the radio-aligned, rest-frame UV morphologies in many high-redshift radio galaxies (HzRGs), also thought to be caused by jet-induced star formation. MO's stellar population is dominated by a 7.5 Myr old, 1.9 × 10^7 M_⊙ instantaneous burst, with a current star formation rate of 0.52 M_⊙ yr^(-1) (concentrated upstream from where the H I column density is high). This is unlike the jet-induced star formation in Centaurus A, where the jet interacts with preexisting cold gas; in MO, the H I may have cooled out of a warmer, clumpy intergalactic or interstellar medium as a result of jet interaction, followed by the collapse of the cooling clouds and subsequent star formation (consistent with numerical simulations). Since the radio source that triggered star formation in MO is much less luminous, and therefore more common than powerful HzRGs, and because the environment around MO is not particularly special in terms of abundant dense, cold gas, jet-induced star formation in the early universe might be even more prevalent than previously thought.