A Radio Study of the Seyfert Galaxy Markarian 6: Implications for Seyfert Life Cycles

We have carried out an extensive radio study with the Very Large Array on theSeyfert 1.5 galaxy Mrk 6 and imaged a spectacular radio structure in thesource. The radio emission occurs on three different spatial scales, from ~7.5kpc bubbles to ~1.5 kpc bubbles lying nearly orthogonal to them and a ~1 kpcradio jet lying orthogonal to the kpc-scale bubble. To explain the complexmorphology, we first consider a scenario in which the radio structures are theresult of superwinds ejected by a nuclear starburst. However, recent Spitzerobservations of Mrk 6 provide an upper limit to the star formation rate (SFR)of ~5.5 M_sun/yr, an estimate much lower than the SFR of ~33 M_sun/yr derivedassuming that the bubbles are a result of starburst winds energized bysupernovae explosions. Thus, a starburst alone cannot meet the energyrequirements for the creation of the bubbles in Mrk 6. We show that a singleplasmon model is energetically infeasible, and we argue that a jet-drivenbubble model while energetically feasible does not produce the complex radiomorphologies. Finally, we consider a model in which the complex radio structureis a result of an episodically-powered precessing jet that changes itsorientation. This model is the most attractive as it can naturally explain thecomplex radio morphology, and is consistent with the energetics, the spectralindex and the polarization structure. Radio emission in this scenario is ashort-lived phenomenon in the lifetime of a Seyfert galaxy which results due toan accretion event.Comment: Accepted for publication in Ap