The excitation and kinematical properties of H2 and [Fe II] in the HH 46/47 bipolar outflow

Abstract

Long-slit spectra of the molecular outflow Herbig-Haro (HH) 46/47 have 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 south-west of HH 46. In contrast with the optical appearance of this object, we show that this outflow seems to be composed of two different emission regions characterized by distinct heliocentric velocities. This implies an acceleration of the counter-jet. The observed [Fe II] 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 [Fe II] emission regions in the northern part of the HH 46/47 outflow. We have detected for the first time high-velocity (-250kms-1) [Fe II] emission in the region bridging HH 46 to HH 47A. The two strong peaks detected can be identified with the optical positions B8 and HH 47B. The H2 excitation diagrams for the counter-jet shock suggest an excitation temperature for the gas of Tex ≈ 2600 K. The lack of emission from the higher energy H2 lines, such as the 4-3 S(3) transition, suggests a thermal excitation scenario for the origin of the observed emission. Comparison of the H2 line ratios with 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 parametrized to fit our data.