Study of McLeish's interacting object

Abstract

We discuss the morphology, kinematics, and physical conditions of the emitting gas of the interacting system IRAS 20048—6621. We present as well numerical simulations of this interacting system, discovered by David McLeish in 1946. The main galaxy (McL A) is an edge-on spiral galaxy with highly distorted NW side. On this side is also located McL B, the perturber galaxy. We determined a distance of 151 Mpc (h=0.75) and a diameter of 70 kpc for McL A. It presents a bright nucleus with broad red emission lines (‹FWHM› ≈ 500 km s-ˡ). McL A has far-IR color indexes closely comparable to NGC 3628, one the few nearby edge-on galaxies which is a bright infrared emitter. Nevertheless, McL A is more luminous (in these bands) than any of the edge-on galaxies in the sample of bright infrared galaxies of Young et al. (1988). The two sides of McL A rotation curve are remarkably di†erent. The N-body model that best reproduces McL A kinematical and morphological data (Kuijken & Dubinski 1995) gives a total mass 7x1011 Mʘ for McL A. Numerical simulations with the TREESPH code closely reproduce the morphology and radial velocity observations. The best scenario for this system is that of a prograde encounter between McL A and B, with McL B's orbit 35º tilted with respect to the spiral disk of McL A and a perigalactic distance of 17.6 kpc. The derived mass ratio is McL B/McL A≈1/26. In the last 5x108 yr the perturber has crossed the main galaxy disk twice, in between it crossed the perigalacticon. According to our simulations, the emitting gas present in McL B has not been stripped out from the McL A disk, so that leads us to conclude that McL B is an irregular or small spiral galaxy.