Supernovae from core-collapse of massive stars drive shocks into the molecular clouds from which the stars formed .
Such shocks affect future star formation from the molecular clouds , and the fast-moving , dense gas with compressed magnetic fields is associated with enhanced cosmic rays .
This paper presents new theoretical modeling , using the Paris-Durham shock model , and new observations at high spectral resolution , using the Stratospheric Observatory for Infrared Astronomy ( SOFIA ) , of the H _ { 2 } S ( 5 ) pure rotational line from molecular shocks in the supernova remnant IC 443 .
We generate MHD models for non-steady-state shocks driven by the pressure of the IC 443 blast wave into gas of densities 10 ^ { 3 } to 10 ^ { 5 } cm ^ { -3 } .
We present the first detailed derivation of the shape of the velocity profile for emission from H _ { 2 } lines behind such shocks , taking into account the shock age , preshock density , and magnetic field .
For preshock densities 10 ^ { 3 } – 10 ^ { 5 } cm ^ { -3 } , the H _ { 2 } emission arises from layers that extend 0.01–0.0003 pc behind the shock , respectively .
The predicted shifts of line centers , and the line widths , of the H _ { 2 } lines range from 20–2 , and 30–4 km s ^ { -1 } , respectively .
The a priori models are compared to the observed line profiles , showing that clumps C and G can be explained by shocks into gas with density 10 ^ { 3 } to 2 \times 10 ^ { 4 } cm ^ { -3 } and strong magnetic fields .
Two positions in clump B were observed .
For clump B2 ( a fainter region near clump B ) , the H _ { 2 } spectrum requires a J-type shock into moderate density ( \sim 10 ^ { 2 } cm ^ { -3 } ) with the gas accelerated to 100 km s ^ { -1 } from its pre-shock location .
Clump B1 requires both a magnetic-dominated C-type shock ( like for clumps C and G ) and a J-type shock ( like for clump B2 ) to explain the highest observed velocities .
The J-type shocks that produce high-velocity molecules may be locations where the magnetic field is nearly parallel to the shock velocity , which makes it impossible for a C-type shock ( with ions and neutrals separated ) to form .