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Date and Time of the Query: 2019-08-24 T14:24:52 PDT
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For refcode 1993AJ....105.1318V:
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Copyright by American Astronomical Society. Reproduced by permission
1993AJ....105.1318V ON THE ORIGIN OF THE Z-SHAPED NARROW-LINE REGION IN THE SEYFERT GALAXY NGC 3516 SYLVAIN VEILLEUX AND R. BRENT TULLY Institute for Astronomy, University of Hawaii, 2680 Woo:1lawn Drive, Honolulu, Hawaii 96822 JONATHAN BLAND-HAWTHORN Department of Space Physics and Astronomy, Rice University, Houston, Texas 77251-1892 Received 1992 October 12; Revised 1992 December 2 ABSTRACT The Hawaii Imaging Fabry-Perot Interferometer (HIFI) was used in a kinematic study of the line-emitting gas in the Seyfert 1 galaxy NGC 3516. The line emission in NGC 3516 is dominated by the nuclear broad line emission and by two curved "filaments" straddling the nucleus which give a Z-shaped appearance to the narrow- line region of this object. In addition, circumnuclear emission is detected out to 25" (~4.4 kpc) from the nucleus. There is an extended high-excitation feature 20" north of the nucleus. Other faint emission blobs suggest a discontinuous Z-shaped structure of larger scale than the inner curved filaments and have some association with the radio structure. The velocity field derived from these data cannot be explained by pure rotational motion. The steepest velocity gradient is along P.A. = 30^deg^, i.e., about 25^deg^ away from the apparent major axis of the galaxy. The gas velocities along each of the bright filaments first reach a peak at a radius of about 4" (~0.7 kpc) and then decrease outward to reach near systemic values at their extremities. There is a clear tendency for the line profiles in the intensity crest of the filaments to be narrower (FWHM ~ 150 km s^-1^) than along their edges (FWHM~250 km s^-1^). Multiple kinematic components are often detected in the profiles in these regions. Comparisons are made between the morphology and kinematics of the line-emitting gas in NGC 3516 and the predictions of a number of models. A precessing twin-jet model in which the line-emitting material is entrained by a precessing radio jet is rather successful at explaining the kinematic data. The precession is swinging the jet toward the line of sight which explains the extreme velocities at the current jet position. The agreement is especially good if deceleration of the entrained material is assumed. Gravity is probably not the main deceleration mechanism as the data require a rather sudden deceleration more suggestive of shocks. If this model is valid, this would make NGC 3516 the least luminous known active galaxy with a precessing jet. An alternative scenario assumes that some of the outflowing gas interacts with the ambient gas of the galaxy. The curved inner filaments represent gas entrained by a radio jet which is deflected by ram pressure from the rotating interstellar medium of the galaxy. Fainter emission at the edges of the inner narrow-line region may be produced by clouds outside the plane of the gaseous disk which are being pulled back by the gravitational potential of the galaxy. As in the cases of other early-type galaxies, the rotation axis of the interstellar medium in NGC 3516 may not coincide with the rotation axis of the stellar component.
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