The neutral hydrogen ring, mass-to-light ratio, and dark halo of the elliptical galaxy IC 2006

Schweizer, F., van Gorkom, J.H., & Seitzer, P. 1989, Ap. J. 338, 770.

Observations of the E1 galaxy IC 2006 are presented, and the imaging, photometric, and spectroscopic data are analyzed. The galaxy is found to be in every respect normal for an elliptical galaxy of its luminosity. It is surrounded by an unusually regular ring of 18.9 kps radius, containing (4.8 + or - 0.8) x 10 to the 8th solar masses of H I that rotates in the opposite sense of the stars near the center. The integrated M/L(B) within the radius of the ring indicates the presence of a halo of dark matter with about twice the mass of the luminous matter. Very weak emission lines reveal a central mass of ionized gas extending to about 5 kpc radius. This gas also rotates counter to the stars and is highly turbulent. The dwarf companion Karachentseva 22 lies at a projected distance of 3.1 ring radii and has one-third as much H I as the ring, but is unlikely to be the donor of the ring H I.