Complex Gaseous Structure in the Nucleus of NGC 5252

Abstract

We present several Hubble Space Telescope (HST) WFPC2 emission-;ine and continuum images of NGC 5252, a Seyfert 2 50 galaxy with a large-scale "ionization bi-cone." In the Hα + [N II] image, the nucleus is bracketed at 0"3 radii by two bright emission-line clumps along P.A. = 35° (∼20° from the major axis of the large-scale stellar disk). These three knots dominate the emission in the innermost ∼1" (∼450 pc at 92 Mpc distance). Two major and several smaller spiral filaments, wound tightly counterclockwise, extend ∼3" to the northwest and ∼4".5 to the southeast of the nucleus. Several of these filaments extend from the two clumps near the nucleus, possibly indicating that the three collinear knots comprise a bar. Our Fabry-Perot velocity map shows that the spiral pattern is rotating, in a disk inclined significantly to both the galaxy stellar disk and the radio jets. The nuclear radio jets appear to have no obvious association with the Hα + [N II] filaments and clumps. Although most of the line flux is emitted within the inward extrapolation of the large- scale ionization bi-cone, some of the Hα + [N II] filaments extend beyond the cone boundaries. A remarkable D-shaped pattern of obscuring dust is visible on the northwest side of the galaxy major axis. Most of the spiral filaments in the Hα + [N II] image also appear in the obscuration map. The extinction by the filaments requires a column density of N_H 5 × 10²⁰ cm^-2. If the filaments are uniformly filled, both the gas responsible for the extinction and the ionized gas responsible for the emission have number densities of a few cm^-3.