ABSTRACT

The kinematics of ionized gas in active (and normal) galaxies is reviewed. For clarity, discussion is divided first by emission region size, and then by galaxy type. Although a wide range of velocity fields are encountered on all scales, a number of recent developments are stressed : large scale outflows in Seyfert and Starburst galaxies (1–20 kpc); gravitationally dominated motion on intermediate scales in all galaxies (few × 102 pc); radial flows of uncertain direction on small scales in Seyferts (3 – 100 pc); and possible continuity of velocity field in Seyferts down to very small scales (≲0.1 pc, BLR).

INTRODUCTION

Ionized gas can be found on many scales in both active and normal galaxies — on large scales ∼ 1 – 20 kpc in the body and near environment of the host galaxy; on intermediate scales ∼ 0.1 – 1 kpc in the bulge dominated regions; on small scales ∼ 3 – 100 pc in the inner bulge cores; and on very small scales ∼ 0.01 – 1 pc within the Broad Line Region (BLR). My intention is to review observations which shed light on the kinematics of this ionized gas, recognizing that the velocity fields on one scale may be quite unrelated to those on another.

Studies of ionized gas kinematics focus, of course, on emission lines and their Doppler profiles. First order information comes from the profile center and width, while higher order information comes from profile asymmetry, kurtosis, and substructure, as well as the comparison of these for different emission lines.