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

Abstract

We have carried out an extensive radio study with the Very Large Array on the Seyfert 1.5 galaxy Mrk 6 and imaged a spectacular radio structure in the source. The radio emission occurs on three different spatial scales: $7.5 kpc bubbles, $1.5 kpc bubbles lying nearly orthogonal to them, and a $1 kpc radio jet lying orthogonal to the kiloparsec-scale bubble. To explain the complex morphology, we first consider a scenario in which the radio structures are the result of superwinds ejected by a nuclear starburst. However, recent Spitzer observations of Mrk 6 provide an upper limit to the star formation rate (SFR) of $5.5 M yr À1 , an estimate much lower than the SFR of $33 M yr À1 derived assuming that the bubbles are a result of starburst winds energized by supernova explosions. Thus, a starburst alone cannot meet the energy requirements for the creation of the bubbles in Mrk 6. We then present an energetically plausible model wherein the bubbles are a result of energy deposited by the kiloparsec-scale jet as it plows into the interstellar medium. Finally, we consider a model in which the complex radio structure is a result of an episodically powered precessing jet that changes its orientation. This model is the most attractive as it can naturally explain the complex radio morphology and is consistent with the energetics, the spectral index, and the polarization structure. Radio emission in this scenario is a short-lived phenomenon in the lifetime of a Seyfert galaxy, which results from an accretion event.

STORM IN A “TEACUP”: A RADIO-QUIET QUASAR WITH ≈10 kpc RADIO-EMITTING BUBBLES AND EXTREME GAS KINEMATICS

“…The radio bubbles of the "Teacup" AGN (see Figure 6) are reminiscent of several of the large-scale ( 1-10 kpc) radio structures observed in local Seyfert galaxies (i.e., lowluminosity AGNs), which are often associated with optical emission-line regions and disturbed ionized gas (e.g., Capetti et al 1996;Colbert et al 1996;Falcke et al 1998;Ferruit et al 1999;Whittle & Wilson 2004;Hota & Saikia 2006;Kharb et al 2006). Furthermore, the morphology of the large-scale arc of ionized gas in the Teacup AGN (Figure 6) is analogous to some local starburst galaxies and AGNs that host "super bubbles," or arcs/filaments of optical emission lines (e.g., Heckman et al 1990;Veilleux et al 1994Veilleux et al , 2001Veilleux et al , 2005Capetti et al 1996;Ferruit et al 1999;Whittle & Wilson 2004; also see the analogous radio-loud AGNs in van Breugel et al 1985 andHatch et al 2013).…”

“…Kharb et al (2006) suggests that the radio jets are ultimately responsible for the creation of the large-scale radio bubbles. Following Kharb et al (2006), we can estimate the particle energy (electrons and protons; E min ) at minimum pressure in the radio bubbles, under the assumption of equipartition of energy between the magnetic field and relativistic electrons and neglecting thermal pressure. We calculate these values following Equations (1) and (4) of O'Dea & Owen (1987) and obtain the relevant constants from Pacholczyk (1970); see Miley (1980) for a discussion on the relative assumptions.…”

“…If we assume that the HR-A and HR-B structures are both dominated by radio jets with α = −1.1 (see Table 2), their combined total radio luminosity is 2.5 × 10 40 erg s −1 (following Equation (1) in O'Dea & Owen 1987) which would result in a jet kinetic luminosity of 2.5 × 10 42 erg s −1 , assuming that 1% of the total jet energy is converted into radio luminosity (following Kharb et al 2006; also see, e.g., Bîrzan et al 2008). This would require the jets to deposit their energy continuously for ≈3.0-230 Myr to produce the derived combined minimum energy of the bubbles.…”

A rare example of low surface-brightness radio lobes in a gas-rich early-type galaxy: the story of NGC 3998

“…In this scenario, the connection between the warping of the gas structure and the morphology of the radio lobes would be that the SMBH spin and, therefore, the jet axis are adapting to the changing angular momentum of the accreting gas. Indeed, such jet precession is expected to generate the radio continuum morphology observed in systems such as Mrk 6 (Kharb et al 2006) and NGC 326 (Ekers et al 1978). …”

From Nearby Low Luminosity AGN to High Redshift Radio Galaxies: Science Interests with Square Kilometre Array

“…Right ascension Declination Figure 5. The Seyfert galaxy Markarian 6 exhibits three sets of radio lobes/jets which are nearly perpendicular to each other (Kharb et al 2006). The detection of these structures required sensitive observations with multiple arrays and frequencies with the VLA and MERLIN.…”