Optical spectroscopy and narrow-band images of the variable Seyfert 1 galaxy NGC 3783

Abstract

We present narrow-band images centered on [O III] λ5007, Hα, and adjacent continua of the Seyfert 1 galaxy NGC 3783. The continuum images evidence that the bar emission is mainly due to old stars. The [O III] λ5007 image shows that the high-excitation gas is very concentrated while the Hα emission is more extended and elongated perpendicularly to the direction of the bar. Ten new optical spectra, obtained between 1987 and 1990, are used to study the variability of the contin­ uum and emission lines in this galaxy. The contribution of the bulge stellar population to the nuclear spec­ trum is determined for each epoch and subtracted. The remaining optical continuum is then decomposed in two variable components, and after these components have been subtracted, the resultant spectra, constituted by pure line emission, are analyzed. A multiple Gaussian components model is found in order to describe the different emission lines on the various spectra. With the results of this decomposition the structure and physi­ cal conditions of the emission-line regions are determined. The variations in the continuum and emission-line fluxes are then analyzed, and the relations between them are pointed out.