THE WARDLE INSTABILITY IN INTERSTELLAR SHOCKS .2. GAS TEMPERATURE ANDLINE EMISSION

We have modeled the gas temperature structure in unstable C-type shock s and obtained predictions for the resultant CO and H-2 rotational lin e emissions, using numerical simulations of the Wardle instability pre sented in Paper I. Our model for the thermal balance of the gas includ es ion-neutral frictional heating; compressional heating; radiative co oling due to rotational and re-vibrational transitions of the molecule s CO, H2O, and H-2; and gas-grain collisional cooling. We obtained res ults for the gas temperature distribution in-and H-2 and CO line emiss ion from-shocks of neutral Alfvenic Mach number 10 and velocity 20 or 40 km s(-1) in which the Wardle instability has saturated. Both two-an d three-dimensional simulations were carried out for shocks in which t he preshock magnetic held is perpendicular to the shock propagation di rection, and a two-dimensional simulation was carried out for the case in which the magnetic held is obliquely oriented with respect to the shock propagation direction. Although the Wardle instability profoundl y affects the density structure behind C-type shocks, most of the shoc k-excited molecular line emission is generated upstream of the region where the strongest effects of the instability are felt. Thus the Ward le instability has a relatively small effect on the overall gas temper ature distribution in-and the emission-line spectrum from-C-type shock s, at least for the cases that we have considered. In none of the case s that we have considered thus far did any of the predicted emission-l ine luminosities change by more than a factor of 2.5, and in most case s the effects of instability were significantly smaller than that. Sli ghtly larger changes in the line luminosities seem likely for three-di mensional simulations of oblique shocks, although such simulations hav e yet to be carried out and lie beyond the scope of this study. Given the typical uncertainties that are always present when model predictio ns are compared with real astronomical data, we conclude that Wardle i nstability does not imprint any clear observational signature on the s hock-excited CO and H-2 line strengths. This result justifies the use of one-dimensional steady shock models in the interpretation of observ ations of shock-excited line emission in regions of star formation. Ou r three-dimensional simulations of perpendicular shocks revealed the p resence of warm filamentary structures that are aligned along the magn etic held, a result that is of possible relevance to models of water m aser emission from C-type shocks.