Molecular and Ionic Shocks in the Supernova Remnant 3C 391

Abstract

New observations of the supernova remnant 3C 391 are presented in the near-infrared, using the H2 2.12 μm and [Fe II] 1.64 μm narrowband filters in the Prime Focus Infrared Camera on the Palomar Observatory Hale 200 inch telescope, and in the mid-infrared, using the circular-variable filters in the ISOCAM on the Infrared Space Observatory. Shocked H2 emission was detected from the broad molecular line region in 3C 391 (3C 391:BML) (40'' size), where broad millimeter CO and CS lines had previously been detected. A small H2 clump, 45'' from the main body of 3C 391:BML, was confirmed to have broad CO emission, demonstrating that the near-infrared H2 images can trace previously undetected molecular shocks. The [Fe II] emission has a significantly different distribution, being brightest in the bright radio bar at the interface between the supernova remnant and the giant molecular cloud, and following filaments in the radio shell. The near-infrared [Fe II] image and the mid-infrared 12-18 μm image (dominated by [Ne II] and [Ne III]) are the first images to reveal the radiative shell of 3C 391. The mid-infrared spectrum is dominated by bright ionic lines of [Fe II] 5.5 μm, [Ar II] 6.9 μm, [Ne II] 12.8 μm, and [Ne III] 15.5 μm, as well as the series of pure rotational lines of H2 S(2) through S(7). There are no aromatic hydrocarbons associated with the shocks, nor is there any mid-infrared continuum, suggesting that macromolecules and very small grains are destroyed in the shocks. Comparing 3C 391 with the better studied IC 443, both remnants have molecular- and ionic-dominated regions; for 3C 391, the ionic-dominated region is the interface into the giant molecular cloud, showing that the main bodies of giant molecular clouds contain significant regions with densities of 102-103 cm-3, and a small filling factor of higher density regions. The broad molecular line region 3C 391:BML was imaged in the 1-0 S(1) line at 15 resolution. The molecular shocked region resolves into 16 clumps of H2 emission, with some fainter diffuse emission, but with no associated near-infrared continuum sources. One of the clumps is coincident with a previously detected OH 1720 MHz maser to within our 03 astrometry. These clumps are interpreted as a cluster of prestellar dense molecular cores that are currently being shocked by the supernova blast wave.