Shocked molecular gas in three supernova remnants : W28, W44, 3C391

Abstract

The three supernova remnants, 3C391, W28 and W44, are known to be interacting with their environmental molecular clouds. Our goal in studying such interactions is to determine whether compression by supernova shocks triggers star formation or whether, on the contrary, the shock destroys the clouds. Another interest in pursuing this research is to distinguish the physical nature of the shocks which occur in these supernova remnants, i.e. either J or C-type shocks.

Observations have been made in both millimeter and near-infrared domains. Molecular observations, which trace the quiescent gas, include the rotational transitions [superscript 12]CO J=3 [arrow right] 2 and [superscript 13]CO J=3 [arrow right] 2, and several other molecules in the 218-363 GHz range. For studying the shocked gas, we made use of v=1-0 S(1) H [subscript 2] as well as Brγ emission observations on several locations close to the shock front.

We are investigating in detail the morphology of the gas near (1720MHz) OH maser locations, which are known to be sites of shocked gas. The analysis consists also of the estimation of the excitation temperatures and column densities of clumps of gas and the determination of their gravitational stability, in order to test the triggering of star formation hypothesis.

The high resolution, both spatial (0.5'') and in velocity (~12 km/s) of the BEAR instrument on CFHT gives for the first time the possibility to resolve the vibrational line H[subscript 2] v=1-0 S(1) in the three remnants. This provides additional information about the local speed of the shocks and their possible physical nature. Also, the absence of Brγ emission puts further constraints on the nature of the shock. We analyse the line intensities of the H[subscript 2] v=1-0 S(1) and the upper limit values for Brγ emission and compare the results with the available theoretical models of shocks. Our study supports the hypothesis of a C-type shock, in agreement with the theoretical picture of the (1720 MHz) OH maser originating conditions.