IC 4329A - The nearest quasar

Abstract

A spectrophotometric study of the Seyfert galaxy IC 4329A has been made with the Anglo-Australian Telescope. Fe II emission is found in the spectrum as well as forbidden lines with ionizations ranging up to (Fe X) lambda6374. The Balmer lines are double peaked, the secondary (more highly redshifted) component having a flatter Balmer decrement than the main one. The equivalent widths of most lines seem to be variable, with changes in the continuum level being the most plausible explanation.That the nucleus of IC 4329A is heavily reddened is indicated by the facts that (i) a prominent dust lane is seen to bisect the nucleus, (ii) the Balmer decrement (H..cap alpha../H..beta..approx. =12) is steeper than found in any other Seyfert galaxy, (iii) the observed nuclear optical continuum is very steep (F/sub ..nu../proportional..nu../sup -4.4/), and (iv) prominent Na I D-line absorption is seen at the redshift of IC 4329A. The values of A/sub upsilon/ derived from (ii), (iii), and (iv) above are 4.8, 2.5, and >1.6 mags, respectively. If Aupsilon lies in the range 2.5--4.8 mag, as seems most likely, the absolute nuclear magnitude M/sub upsilon/ lies in the range -23.0 to -25.3, values typical of quasars. The observations of the Namore » I D lines have also been used to deduce that the velocity dispersion of the absorbing sodium atoms lies in the range 8.4--13.5 km s/sup -1/ with 90% confidence. This small dispersion suggests that noncircular motions in the disk of IC 4329A are small and that the velocity dispersion of its interstellar medium is quite comparable to that in our Galaxy, contrary to theoretical speculations that the interstellar medium in Seyferts might be seriously disrupted.« less