THE H-I-RICH ELLIPTIC GALAXY NGC-5266

We present new H I images of the dust-lane elliptical galaxy NGC 5266 already known from single-dish observations to contain a large amount of H I. Our new data confirm that NGC 5266 contains similar to 2.4 x 1 0(10) M(circle dot) (for H-0 = 50 km s(-1) Mpc(-1)) of neutral hydroge n, i.e., more than most spiral galaxies of similar luminosity. The gas extends to similar to 8' each side of the nucleus, or 8 times the opt ical half-light radius R(e). Surprisingly, most of the H I extends alm ost orthogonal to the optical dust lane. A small fraction of the H I i s associated with the dust lane and there are some hints of a faint wa rp connecting the two structures. The H I distribution is somewhat clu mpy and asymmetric, but the overall velocity field in the inner 4' can be successfully modeled by assuming that the gas lies mainly in two p erpendicular planes-in the plane of the dust lane in the central parts and orthogonal to this in the outer regions. Beyond the 4' radius, th e gas has a different structure and may be in two tidal tails, or an e dge-on ring. Measurement of the H I rotation curve is affected by asym metries in the gas distribution, but the rotation velocity is at least 250 km s(-1) at a radius of 4', and a flat rotation curve of similar to 270 km s(-1) is consistent with the data. This would imply a value of M/L(B) similar to 8 at similar to 4 R(e). If the outermost H I is i n an edge-on ring, we estimate M/L(B) similar to 16 at similar to 8 R( e). Comparing this with the value derived from optical observations fo r the inner region we find an increase of M/L(B) by a factor similar t o 2.7 at r similar to 4 R(e), and by 5.3 at r similar to 8 R(e). The l arge amount of neutral gas observed in NGC 5266 (M(H I)/L(B) similar t o 0.2) and the H I morphology, suggest that this object may have forme d from the merger of two spiral galaxies. If so, NGC 5266 probably rep resents a relatively old merger remnant since most of the H I gas appe ars settled. (C) 1997 American Astronomical Society.