Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published January 1, 2005 | Published + Submitted
Journal Article Open

Shocked Molecular Gas in the Supernova Remnants W28 and W44: Near-Infrared and Millimeter-Wave Observations

Abstract

High-resolution millimeter-wave (CO, CS, and HCO^+ rotational lines) and near-infrared (H_2 2.12 μm rovibrational and Fe II fine-structure lines) observations of the supernova remnants W28 and W44 reveal extensive shocked molecular gas, where supernova blast waves are propagating into giant molecular clouds. New CO observations were carried out with the IRAM 30 m and Arizona Radio Observatory 12 m telescopes, and the near-infrared observations were with the PFIRCAM and Wide-Field Infrared Camera on the Palomar Hale 200 inch (5.08 m) telescope. The near-infrared observations reveal shocked H2 emission from both supernova remnants, showing intricate networks of filaments on arcsecond scales, following the bright ridges of the radio shells. The emission is particularly bright in the northeastern, southern, and western parts of W44 and in the eastern bar in W28. The H_2 emission reveals some bright, clumpy structures, as well as very thin filamentary structures likely to be individual shock fronts seen edge-on. The high-resolution IRAM CO(2 → 1) and CS(2 → 1) spectra clearly distinguish between the shocked and preshock gas for most of the supernova remnants. Some of the CO spectra appear to have multiple components, but the less optically thick 13CO lines clearly demonstrate that the CO(2 → 1) lines are broad, with deep absorption dips caused by cold, dense gas in the line of sight. The CO and CS line widths, indicative of the shock speed, are 20-30 km s^(-1). Both the near-infrared and millimeter-wave emission are attributed to shocks into gas with density higher than 10^3 cm^(-3). Individual shock structures are resolved in the H2 emission, with inferred edge-on shock thicknesses of ~10^(17) cm, consistent with nondissociative shocks into gas densities of 10^3-10^4 cm^(-3). Bright 1720 MHz OH masers are located within the shocked H_2 gas complexes and highlight only localized areas, where the conditions for masing are optimal. The Hα and X-ray emission, which trace hotter shocked gas, have morphologies very different from the radio. We find a detailed correlation of the radio and H2 emission for some long filaments, indicating cosmic-ray acceleration or reacceleration due to shocks into moderately dense gas. Compared to the interclump gas and the very dense cores, the synchrotron emissivity of the moderate-density (CO emitting) medium is highest, which explains the radio-H_2 correlation and the very bright radio emission of these two supernova remnants despite their relatively advanced age. The different morphologies of these two remnants at different wavelengths are explained by the highly nonuniform structure of giant molecular clouds, with low-density (~5 cm^(-3)) gas occupying most (~90%) of the volume, moderate-density gas (~10^3 cm^(-3)) gas occupying most of the rest of the volume, and dense gas in the cores.

Additional Information

© 2005. The American Astronomical Society. Received 2004 May 24; accepted 2004 August 31. This work is based on observations obtained at the Hale Telescope, Palomar Observatory, as part of a continuing collaboration between the California Institute of Technology, the NASA Jet Propulsion Laboratory, and Cornell University. We are pleased to acknowledge the assistance of Naman Bhatt, who worked with us for a summer on this project. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, California Institute of Technology, funded by NASA and the National Science Foundation. Observations with the 12 m telescope were made while that telescope was being operated by the NRAO. The NRAO is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. The research described in this paper was carried out at the California Institute of Technology under a contract with NASA.

Attached Files

Published - pdf

Submitted - 0409414.pdf

Files

0409414.pdf
Files (5.0 MB)
Name Size Download all
md5:efc6d8b0c9bccd40c159f68957c49e7a
311.3 kB Preview Download
pdf
md5:507372ca3c64e9c75c8ecbf159cd37b4
4.7 MB Preview Download

Additional details

Created:
August 22, 2023
Modified:
October 25, 2023