Orion B (NGC 2024). II. Hat creek synthesis observations of the molecular core in the J = 1 → 0 line of HCO⁺

We present the first aperture synthesis maps of HCO⁺ J = 1 → 0 emission at 89 GHz of the molecular cloud Orion B obtained with the Hat Creek Array. The spatial resolution is 11″ × 8″ and the velocity resolution is 0.53 km s^-1. The maps show much fine structure in the dense molecular core, including a centrally located broad-line region with an elliptical velocity distribution and apparently centered on the farinfrared source FIR 6, a long, quiescent, NS-oriented ridge at a P.A. of -10° with a similar appearance to the cold dust emission, an EW ridge which exactly abuts the ionization front of the adjacent H II region, and a possible one-sided high-density outflow to the south with an origin apparently not near any of the near-infrared (NIR) sources but instead close to FIR 5. FIR 5 and 6 therefore seem to indicate two different centers of activity in the molecular core. We do not detect any emission from the optically visible dust lane, possibly suggesting a lower density than the core for this foreground molecular gas.