Looking into the Horsehead

We present the first interferometric CO (1–0) map of the Horsehead Nebula, made with the Berkeley-Illinois-Maryland Association array. The map has an angular resolution of about 10'', corresponding to about 0.02 pc. The CO form of the Horsehead closely matches its appearance in visible dust, with the CO emission dominated by a bright, thin ridge along its western side. The molecular cloud exhibits a pronounced velocity gradient of 5 km s-1 pc-1 from the northeast to the southwest, with the southwestern portion being redshifted. The mass of the cloud is 27 M⊙. We find an unusual U-shaped feature aligned with the "horse's nose" for which we discuss several interpretations. The northern portion of the U may trace a small outflow driven by the embedded young star B33-1. We discuss the formation, evolution, and ultimate fate of this well-known nebula.