NGC 6438

Abstract

We provide photographic and photoelectric information as well as CCD imaging and medium resolution spectroscopy on this system located at a distance of -32 Mpc. The SO galaxy has twisted isophotes which also show changes in the ellipticity. Profiles toward the north of this galaxy are 0.1 and 0.2 magnitudes brighter in the B and V bands respectively, than in any other direction, probably due to the presence of dust in the Irregular system. Several blue regions (B-V = 0.26 - 0.40) are found in the Irregular object indicating ongoing star formation. One of these regions is located in an extreme of the northern arm, its luminosity being similar to that of the nucleus which is very close to it. Analysis of the spectra shows typical absorption lines and a weak [Nil] emission in the SO galaxy whereas Ha, [Nil] and [SII] emission lines are observed both in the nucleus and in the blue region mentioned above. We determine a high reddening E(B-V) = 1.4 in the nuclear region of this system. Rotation curves show a different behavior for the nucleus and the blue region, which have Vmax >180 km/sec and Vmax = 80 km/sec respectively. All tins evidence could support the idea that NGC 6438 is an interacting triplet, one SO galaxy and two disk galaxies undergoing a merger.