2010ApJ...720...64B

The outflow driven by the Class 0 protostar, IRAS 16253-2429, is associated with bipolar cavities visible in scattered mid-infrared light, which we refer to as the Wasp-Waist Nebula. InfraRed Spectometer (IRS) scan mapping with the Spitzer Space Telescope of a ∼1'x2' area centered on the protostar was carried out. The outflow is imaged in six pure rotational (0-0 S(2) through 0-0 S(7)) H₂lines, revealing a distinct, S-shaped morphology in all maps. A source map in the 11.3 µm polycyclic aromatic hydrocarbon (PAH) feature is presented in which the protostellar envelope appears in absorption. This is the first detection of absorption in the 11.3 µm PAH feature. Spatially resolved excitation analysis of positions in the blue- and redshifted outflow lobes, with extinction-corrections determined from archival Spitzer 8 µm imaging, shows remarkably constant temperatures of ∼1000 K in the shocked gas. The radiated luminosity in the observed H₂ transitions is found to be 1.94±0.05x10^–5 L_☉ in the redshifted lobe and 1.86±0.04 x10^–5 L_☉ in the blueshifted lobe. These values are comparable to the mechanical luminosity of the flow. By contrast, the mass of hot (T ∼ 1000 K) H₂ gas is 7.95±0.19x10^–7 M_☉in the redshifted lobe and 5.78±0.17x10^–7 M_☉ in the blueshifted lobe. This is just a tiny fraction, of order 10^–3, of the gas in the cold (30 K), swept-up gas mass derived from millimeter CO observations. The H₂ortho/para ratio of 3:1 found at all mapped points in this flow suggests previous passages of shocks through the gas. Comparison of the H₂ data with detailed shock models of Wilgenbus et al. shows the emitting gas is passing through Jump (J-type) shocks. Pre-shock densities of 10⁴/cm3≤ n_H≤ 10⁵/cm3 are inferred for the redshifted lobe and n_H≤ 10³/cm3 for the blueshifted lobe. Shock velocities are 5 km/s ≤ v_s≤ 10 km/s for the redshifted gas and v_s= 10 km/s for the blueshifted gas. Initial transverse (to the shock) magnetic field strengths for the redshifted lobe are in the range 10-32 µG, and just 3 µG for the blueshifted lobe. A cookbook for using the CUBISM contributed software for IRS spectral mapping data is presented in the Appendix.