2008AJ....136.1947W

NGC 2024 is a star-forming region in Orion B that contains a dense molecular ridge. A number of dense cores are seen by their dust emission. This area is investigated using observations of four formaldehyde transitions–namely, 3₀₃ ⟶ 2₀₂, 3₂₂ ⟶ 2₂₁, 5₀₅ ⟶ 4₀₄, and 5₂₃ ⟶ 4₂₂. Maps of the ridge are used to provide temperatures and densities, with a focus on the dense-core positions. The formaldehyde transition ratios 3₀₃ ⟶ 2₀₂/3₂₂ ⟶ 2₂₁ and 5₀₅ ⟶ 4₀₄/5₂₃ ⟶ 4₂₂ offer measurements of the kinetic temperature, while the ratio 3₀₃ ⟶ 2₀₂/5₀₅ ⟶ 4₀₄ allows the evaluation of number densities. The resulting temperatures are very warm (45-85 K), with no observed variation between the core centers and their envelopes. H₂ CO number densities of ∼2x10⁶ cm^–3 at far-infrared (FIR) core positions and H₂ CO column densities in the range of 6x10¹⁴ to 1x10¹⁵ cm^–2 are derived. Using the derived properties in combination with previous submillimeter continuum data, core masses of ∼2 M_☉ are found within a 15'' beam size. H₂CO fractional abundances are calculated and resemble previous values found in similar star-forming regions–between 2x10^–9 and 5x10^–9. The virial theorem applied to FIR cores 3, 4, 5, and 6 suggests that all four cores are unstable against gravitational collapse.