The Origin of the Narrow‐Line Region of Markarian 3: An Overpressured Jet Cocoon

We have obtained HST FOC long-slit optical spectroscopy of the Narrow LineRegion of the Seyfert 2 galaxy Mrk 3. In the region cospatial with theradio-jet the velocity field is highly perturbed and shows two velocity systemsseparated by as much as 1700 km/s. We interpret this to be the consequence ofthe rapid expansion of a cocoon of hot gas, shocked and heated by theradio-emitting outflow, which compresses and accelerates the ambient gas. TheNLR itself is essentially a cylindrical shell expanding supersonically. Fromthe size and velocity of the expanding region, we derive an upper limit to theradio-source age, ~< 1.5 E5 years, and a lower limit for the jet power, ~> 2E42 erg/s required to inflate the cocoon and estimate that the jet minimumadvance speed is 3 E-3 pc per year. The total kinetic energy of the highvelocity NLR gas can be estimated as ~6 E54 erg, comparable to the total energycarried by the jet over its lifetime and this quantitatively supports the ideathat the NLR gas is accelerated by the jet. If the advance speed of Mrk 3 isrepresentative of the Seyfert population then these sources must also be shortlived and probably recurrent. The jet kinetic luminosity of Mrk 3 is between 2and 3 orders of magnitude smaller than that derived for radio-loud AGNs withsimilar emission-line luminosity. On the other hand, the fraction of jet powerdissipated in radio-emission is similar. We speculate that the main distinctionbetween radio-quiet and radio-loud AGN is ascribed to a difference in jet powerrather than to a different efficiency in synchrotron emission production.Comment: 13 pages, 8 figures, Astrophysical Journal in pres