The excitation and kinematical properties of H2 and [FeII] in the HH46/47 bipolar outflow

Abstract

Long slit spectra of the molecular outflow Herbig-Haro (HH) 46/47 has been taken in the J and K near-infrared bands. The observed H2 line emission confirms the existence of a bright and extended redshifted counter-jet outflow southwest of HH46. We show that this outflow seems to be composed of two different emission regions which have distinct heliocentric velocities, in contrast with the optical appearance, and which implies an acceleration of the counter-jet. The observed [FeII] emission suggests an average extinction of 7-9 visual magnitudes for the region associated with the counter-jet. Through position-velocity diagrams, we show the existence of different morphologies for the H2 and [FeII] emission regions in the northern part of the HH46/47 outflow. We have detected for the first time high velocity (-250 Km/s) [FeII] emission in the region bridging HH46 to HH47A. The two strong peaks detected can be identified with the optical positions B8 and HH47B. The H2 excitation diagrams for the counter-jet shock suggest an excitation temperature for the gas of Tex approx. 2600K. The lack of emission from the higher energy H2 lines such as the 4-3S(3) transition, suggests a thermal excitation scenario for the origin of the observed emission. Comparison of the H2 line ratios to various shock models yielded useful constraints about the geometry and type of these shocks. Planar shocks can be ruled out whereas curved or bow-shocks (both J and C-type) can be parametrised to adjust our data.