Large-scale outflows in edge-on Seyfert galaxies. III. Kiloparsec-scale soft X-ray emission

We present ROSAT PSPC and HRI images of eight galaxies selected from a distance-limited sample of 22 edge-on Seyfert galaxies. Kiloparsec-scale soft X-ray nebulae extend along the galaxy minor axes in three galaxies (NGC 2992, NGC 4388, and NGC 5506). The extended X-ray emission has 0.2-2.4 keV X-ray luminosities of 0.4-3.5 x 10(40) ergs s(-1). The X-ray nebulae are roughly cospatial with the large-scale radio emission, suggesting that both are produced by large-scale galactic outflows. Assuming pressure balance between the radio and X-ray plasmas, the X-ray filling factor is greater than or similar to 10(4) times larger than the radio plasma filling factor, suggesting that large-scale outflows in Seyfert galaxies are predominantly winds of thermal X-ray-emitting gas. We favor an interpretation in which large-scale outflows originate as active galactic nucleus-driven jets that entrain and heat gas on kiloparsec scales as they make their way out of the galaxy. Active galactic nucleus-and starburst-driven winds are also possible explanations in cases where the winds are oriented along the rotation axis of the galaxy disk.