AAS 199th meeting, Washington, DC, January 2002
Session 99. AGN - Narrow Line and Broad Line
Display, Wednesday, January 9, 2002, 9:20am-6:30pm, Exhibit Hall

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[99.03] Physical Conditions in the Narrow Line Region of M51

L.D. Bradley II, M.E. Kaiser (JHU), W.A. Baan (NFRA, WSRT)

We present long-slit Space Telescope Imaging Spectrograph (STIS) and Very Large Array ({\em VLA}) observations of the near-nuclear region of M51 obtained to study the kinematic and ionization structure of multiple emission line clouds in the narrow line region (NLR). The STIS spectra were obtained at a single position angle (166\circ) which intersects the nucleus and several NLR clouds. Low-dispersion G430L and G750L spectra provide continuous wavelength coverage from 2900 Å\ to 1 micron, while G430M spectra of [OIII] (66 km\,s-1 resolution) were used to more precisely determine the velocity structure of the emission-line clouds. The {\em VLA} radio continuum observations obtained at 3.6~cm with a resolution of 0.24\arcsec\ complement our high spatial resolution (0.1\arcsec) {\em HST}/STIS spectra.

M51 possesses a biconical ionization cone (Ford et al. 1985, Cecil 1988) typical of Seyferts and Liners. This near-nuclear emission is comprised of multiple knots spanning 3.0\arcsec (122\,pc) with cloud separations ranging from 0.1\arcsec (4\,pc) to 0.75\arcsec (31\,pc). Our 3.6\,cm radio observations exhibit elongated nuclear emission with a similar PA. In agreement with earlier lower resolution 6\,cm data (Crane & van der Hulst 1992), a weak radio jet, ~2.5\arcsec in extent, connects the near-nuclear emission with a diffuse (lobe) structure which spans ~4\arcsec\ (163\,pc). Close to the northern edge of this diffuse structure lies a radio knot which is identified with the extra-nuclear cloud (XNC) detected in H\alpha\,+\,[NII] and [OIII] imaging (Ford et al. 1985; Grillmair et al. 1997) and the X-ray (Terashima & Wilson 2001). We also detect weak radio emission extending to the north of the nucleus roughly opposite the southern jet. This northern 10\muJy radio contour encompasses the [OIII] emission structure ~1.2\arcsec\ north of the nucleus.

Cloud velocities, velocity dispersions, emission line flux ratios, and photoionization modelling will be presented and discussed to explore the physical conditions (reddening, temperature, density, and ionization state) of the inner NLR gas.

Support for these observations was provided by contract NAS5-30403.

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