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

We present neutral hydrogen, ultraviolet, optical and near-infrared imaging,and optical spectroscopy, of Minkowski's Object (MO), a star forming peculiargalaxy near NGC 541. The observations strengthen evidence that star formationin MO was triggered by the radio jet from NGC 541. Key new results are thediscovery of a 4.9E8 solar mass double HI cloud straddling the radio jetdownstream from MO, where the jet changes direction and decollimates; strongdetections of MO, also showing double structure, in UV and H-alpha; andnumerous HII regions and associated clusters in MO. In UV, MO resembles theradio-aligned, rest-frame UV morphologies in many high redshift radio galaxies(HzRGs), also thought to be caused by jet-induced star formation. MO's stellarpopulation is dominated by a 7.5 Myr-old, 1.9E7 solar mass instantaneous burst,with current star formation rate 0.52 solar masses per year (concentratedupstream from where the HI column density is high). This is unlike thejet-induced star formation in Centaurus A, where the jet interacts withpre-existing cold gas; in MO the HI may have cooled out of a warmer, clumpyintergalactic or interstellar medium as a result of jet interaction, followedby collapse of the cooling clouds and subsequent star formation (consistentwith numerical simulations). Since the radio source that triggered starformation in MO is much less luminous, and therefore more common, than powerfulHzRGs, and because the environment around MO is not particularly special interms of abundant dense, cold gas, jet-induced star formation in the earlyuniverse might be even more prevalent than previously thought.Comment: 52 pages, 15 figures, accepted for publication in Ap