Looking into the Horsehead

Abstract

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 00 , 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 À1 pc À1 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.