The Resolved Narrow Line Region in NGC4151

Abstract

We present slitless spectra of the Narrow Line Region (NLR) in NGC4151 from the Space Telescope Imaging Spectrograph (STIS) on HST, and investigate the kinematics and physical conditions of the emission line clouds in this region. Using medium resolution (~0.5 Angstrom) slitless spectra at two roll angles and narrow band undispersed images, we have mapped the NLR velocity field from 1.2 kpc to within 13 pc (H_o=75 km/s/Mpc) of the nucleus. The inner biconical cloud distribution exhibits recessional velocities relative to the nucleus to the NE and approaching velocities to the SW of the nucleus. We find evidence for at least two kinematic components in the NLR. One kinematic component is characterized by Low Velocities and Low Velocity Dispersions (LVLVD clouds: |v| < 400 km/s, and Delta_v < 130 km/s). This population extends through the NLR and their observed kinematics may be gravitationally associated with the host galaxy. Another component is characterized by High Velocities and High Velocity Dispersions (HVHVD clouds: 400 < |v| < ~1700 km/s, Delta_v > 130 km/s). This set of clouds is located within 1.1 arcsec (~70pc) of the nucleus and has radial velocities which are too high to be gravitational in origin, but show no strong correlation between velocity or velocity dispersion and the position of the radio knots. Outflow scenarios will be discussed as the driving mechanism for these HVHVD clouds.