The L1457 molecular/atomic cloud complex: H I and CO maps.

L1457 is the closest known molecular cloud (65 pc), and it lies near the edge of the local hot bubble and well out of the Galactic plane (b approximately -34 degrees). We have mapped an 8 degrees x 8 degrees region at 35' resolution and a 3 degrees x 5 degrees region at approximately 2' resolution in H I 21 cm emission. We have also mapped a 2 degrees x 4 degrees region at 2' resolution in 12CO J = 1-0. We find that there is an extended component of atomic gas, clearly associated with the molecular complex and comparable to it in total mass. The H I structure at small scales in the vicinity of the molecular clouds is remarkable, consisting largely of long, narrow filaments less than 20' (0.2 pc) in width and 1 degree-4 degrees in length. A thin (<10') limb-brightened atomic halo is seen to surround the CO at some velocities, but it is ill-defined at other velocities. The halo may be disturbed by external pressure, perhaps from the hot gas in the local bubble. The molecular clouds are part of a large structure approximately 5 degrees x 3 degrees in extent with a small "funnel-shaped" extension to the south. The structure, which we call the L1457 atomic/molecular complex, is dominated by H I in the north and H2 in the south extension. Roughly one-half the mass of the complex is molecular. The structure of this complex at both large- and small-scale suggests that the south end has been recently compressed.