A COMPLETE ARECIBO MAP OF H1 1225+01

Complete H I observations at a 3.3' resolution are reported of H I 1225 + 01, a large gas cloud discovered in 1989 by Giovanelli and Haynes. The new observations reveal that the object is composed of two main parts (the NE and the SW clumps) of comparable size and gas content. The NE clump-larger by a factor of 2 than the other-harbors a dwarf irregular galaxy that exhibits two main regions of starburst activity and a fainter background of blue stars. The SW clump has no optical counterpart detected as yet. The velocity fields are used to estimate total masses for each clump and for the cloud as a whole: inferred values for the NE clump, the SW clump, and the whole system, respectively, are 1.3 x 10(10) d20 M ., greater-than-or-equal-to 0.2 x 10(10) d20 M., and 3.6 x 10(10)d M. to be compared with the H I masses of, respectively, 2.4 x 10(9)d20(2) M., 1.3 x 10(9)d20(2) M., and 4.9 x 10(9)d20(2) M., at an assumed distance of d20 in 20 Mpc units. All the dynamical timescales associated with H I 1225 + 01 and its individual components are very long, confirming earlier suggestions that the system is relatively unevolved.