Large-Scale Outflows in Edge-on Seyfert Galaxies. II. Kiloparsec-Scale Radio Continuum Emission

Abstract

We present deep images of the kpc-scale radio continuum emission in 14 edge-on galaxies (ten Seyfert and four starburst galaxies). Observations were taken with the VLA at 4.9 GHz (6 cm). The Seyfert galaxies were selected from a distance-limited sample of 22 objects (defined in paper I). The starburst galaxies were selected to be well-matched to the Seyferts in radio power, recessional velocity and inclination angle. All four starburst galaxies have a very bright disk component and one (NGC 3044) has a radio halo that extends several kpc out of the galaxy plane. Six of the ten Seyferts observed have large-scale (radial extent ∼ >1 kpc) radio structures extending outward from the nuclear region, indicating that large-scale outflows are quite common in Seyferts.Large-scale radio sources in Seyferts are similar in radio power and radial extent to radio halos in edge-on starburst galaxies, but their morphologies do not resemble spherical halos observed in starburst galaxies. The sources have diffuse morphologies, but, in general, they are oriented at skewed angles with respect to the galaxy minor axes. This result is most easily understood if the outflows are AGN-driven jets that are somehow diverted away from the galaxy disk on scales ∼ >1 kpc. Starburst-driven winds, however, cannot be ruled out. More observational work is needed to determine whether massive star formation is present at high enough rates to drive galactic winds out to kpc scales in Seyfert galaxies.

A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei

“…In contrast to the sample of Colbert et al (1996a), the present sample is not limited by host-galaxy inclination and is larger: 43 active galaxies in the present sample versus 10 in Colbert et al We further employed the VLA in the D configuration for improved surface brightness sensitivity. The primary goals of the present study are to assess the commonness of Seyfert KSRs and to search for clues as to their origin.…”

“…The central radio source is unresolved by long-baseline VLA and MERLIN observations (Ulvestad & Wilson 1984b;Kukula et al 1995;Ho & Ulvestad 2001;Thean et al 2001b). Colbert et al (1996a) first detected the arcminute-scale radio features located east and west of the nucleus in their 5 GHz VLA C-configuration images. The present D-configuration images recover additional extended emission, and the radio structures resemble lobes of a jet connecting back to the central unresolved continuum source.…”

“…We estimated the intrinsic properties of the KSR radio sources following the example of Colbert et al (1996a;N.B. : five sources overlap between their sample of edge-on Seyferts and the present survey).…”

“…Scaling to this maximum-loss field strength, the maximum timescale is therefore max ¼ 29( /5 GHz) À1 = 2 Myr. Of course, the AGN and any accompanying starburst produce additional microwave radiation; the microwave luminosity is $10% the bolometric luminosity (Spinoglio et al 1995;Nenkova et al 2002 and references therein), and the resulting equivalent field at a distance of l kpc kiloparsecs from the AGN and ( presumed compact) star- Colbert et al (1996a), relativistic outflows are not required to produce the KSR sources.…”

Hubble Space Telescope WFPC2 Imaging of a Sample of Early‐Type Seyfert Galaxies

“…1, bottom right-hand panel). In the central 5A (850 pc), the radio emission displays a weak elongation along P.A.^180¡ (Colbert et al 1996b ;Nagar et al 1999) and is not aligned with the emission-line region. This lack of correlation between the distributions of radio emission and ionized gas, the high excitation of the nuclear line emission, and the small widths of the low to medium excitation lines observed in this object (De Robertis & Osterbrock 1986) Figure 3 (top and middle panels).…”