FOS Spectroscopy of Several Clouds in the NLR of NGC 4151

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Session 64 -- Low Luminosity AGNs and Active Galaxies
Oral presentation, Thursday, 2, 1994, 10:00-11:30

[64.01] FOS Spectroscopy of Several Clouds in the NLR of NGC 4151

Z.I.\,Tsvetanov, G.A.\,Kriss (JHU), I.N.\,Evans (STScI), H.C.\,Ford (JHU)

We present 0\as3 aperture spectroscopy of the nucleus and some of the emission-line clouds in the inner 1$''$ of the Narrow Line Region of the classical Seyfert galaxy NGC 4151. The observations were obtained with the Faint Object Spectrograph prior to the HST servicing mission.

Very small velocity differences of all but one of the individual clouds and the nucleus are consistent with the NLR being very close to the plane of the sky, and the sense of rotation is in agreement with previous observations. In the off-nuclear spectra we do not see direct evidence for broad lines or nuclear continuum scattered into our line of sight, but properties of the pre-COSTAR PSF do not allow us to put very strict limits.

All clouds show high excitation spectra which are consistent with illumination by a hard AGN continuum. Our wide wavelength coverage allows us to estimate the ionizing parameter from different line ratios, which is of order $\sim$0.01 with very little spread. This combined with the high measured density of individual clouds ($\sim$1000 cm$^{-3}$) leads to an estimate of the number of ionizing photons seen by the clouds. This number is 1.5--2 orders of magnitude lower than previous ground-based estimates and eliminates the so-called `photon deficit' in the case of NGC 4151.

This work is supported by NASA grant NAS 5-1630 to the FOS team.

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