Kinematics of the Narrow-Line Region in the Seyfert 2 Galaxy Markarian 3

We present measurements of radial velocities for the narrow-line region gas in the Seyfert 2 galaxy Mrk 3 out to ∼1 kpc from the nucleus. The observations consist of two data sets, both using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope: (1) an [O III] slitless spectrum with the G430M grating of the inner 3″ around the nucleus and (2) a long-slit observation centered on the nucleus (P.A. = 71°) by using the G430L grating and the 52″ × 0.″1 aperture. Our analysis produces radial velocity maps of the emission-line gas, which indicate trends in the gas motion. These include blueshifts and redshifts on either side of the nucleus, steep velocity rises from systemic up to about ±700 km s-1 taking place in the inner 0.″3 (0.08 kpc) both east and west of the nucleus, gradual velocity descents back to near-systemic values from 0.″3–1.″0, slightly uneven velocity amplitudes on each side of the nucleus, and narrow velocity ranges over the entire observed region. When fitted to kinematic models for the NLR gas, the data clearly favor one in which the gas exists in a partially filled bicone, is accelerated radially away from the nucleus, and is followed by a constant deceleration (possibly due to collision with an ambient medium). This geometry and general kinematic model are in agreement with previous work done on the NLR gas of NGC 1068 and NGC 4151. On scales of hundreds of parsecs, we conclude that radial outflow may be a common feature of Seyfert galaxies.