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Register a new userIdentification of Ambient Molecular Clouds Associated with Galactic Supernova Remnant IC443
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The Galactic supernova remnant (SNR) IC443 is one of the most studied core-collapse SNRs for its interaction with molecular clouds. However, the ambient molecular clouds with which IC443 is interacting have not been thoroughly studied and remain poorly understood. Using Five College Radio Astronomy Observatory 14m telescope, we obtained fully sampled maps of ~ 1{deg} times 1{deg} region toward IC443 in the 12CO J=1-0 and HCO+ J=1-0 lines. In addition to the previously known molecular clouds in the velocity range v_lsr = -6 to -1 km/s (-3 km/s clouds), our observations reveal two new ambient molecular cloud components: small (~ 1) bright clouds in v_lsr = -8 to -3 km/s (SCs), and diffuse clouds in v_lsr = +3 to +10 km/s (+5 km/s clouds). Our data also reveal the detailed kinematics of the shocked molecular gas in IC443, however the focus of this paper is the physical relationship between the shocked clumps and the ambient cloud components. We find strong evidence that the SCs are associated with the shocked clumps. This is supported by the positional coincidence of the SCs with shocked clumps and other tracers of shocks. Furthermore, the kinematic features of some shocked clumps suggest that these are the ablated material from the SCs upon the impact of the SNR shock. The SCs are interpreted as dense cores of parental molecular clouds that survived the destruction by the pre-supernova evolution of the progenitor star or its nearby stars. We propose that the expanding SNR shock is now impacting some of the remaining cores and the gas is being ablated and accelerated producing the shocked molecular gas. The morphology of the +5 km/s clouds suggests an association with IC443. On the other hand, the -3 km/s clouds show no evidence for interaction.
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Narrow passband optical images of the large Galactic supernova remnant G179.0+2.6 reveal a faint but nearly complete emission shell dominated by strong [O III] 4959,5007 A line emission. The remnants optical emission, which consists of both diffuse and filamentary features, is brightest along its southern and northeastern limbs. Deep H-alpha images detect little coincidence emission indicating an unusually high [O III]/H-alpha emission ratio for such a large and apparently old remnant. Low-dispersion optical spectra of several regions confirm large [O III]/H-alpha line ratios with typical values around 10. The dominance of [O III] emission for the majority of the remnants optical filaments suggests shock velocities above 100 km/s are present throughout most of the remnant, likely reflecting a relatively low density ambient ISM. The remnants unusually strong [O III] emission adds to the remnants interesting set of properties which include a thick radio emission shell, radial polarization of its radio emission like that typically seen in young supernova remnants, and an unusually slow-rotating gamma-ray pulsar with a characteristic spin-down age ~50 kyr.
We present the result of near-infrared (near-IR) [Fe II] line mapping of the supernova remnant IC443 with the IRSF/SIRIUS, using the two narrow-band filters tuned for the [Fe II] 1.257 micron and [Fe II] 1.644 micron lines. Covering a large area of 30 x 35, our observations reveal that [Fe II] filamentary structures exist all over the remnant, not only in an ionic shock shell, but also in a molecular shock shell and a central region inside the shells. With the two [Fe II] lines, we performed corrections for dust extinction to derive the intrinsic line intensities. We also obtained the intensities of thermal emission from the warm dust associated with IC443, using the far- and mid-IR images taken with AKARI and Spitzer, respectively. As a result, we find that the [Fe II] line emission relative to the dust emission notably enhances in the inner central region. We discuss causes of the enhanced [Fe II] line emission, estimating the Fe+ and dust masses.
We investigate properties of the interstellar medium (ISM) interacting with shocks around the Galactic supernova remnant IC443, using the results of near-infrared [FeII] and H2 line mapping with the IRSF/SIRIUS. In the present study, we newly performed H2 1-0 S(1) and 2-1 S(1) line mapping with the narrow-band filters tuned for these lines, covering the entire remnant (30x35). Combined with an [FeII] line map, our result shows that the H2 line emission is significantly detected in the southern region, while the [FeII] line emission is detected all over the remnant, suggesting that slow and fast shocks propagate through the southern region and the entire remnant, respectively. In particular, the H2 line emission is relatively strong compared to the [FeII] line emission in the southwestern region, where TeV gamma-ray emission is detected. As the strong H2 line emission indicates the dominance of the dense ISM, this result supports the scenario that the gamma-ray emission is likely to be produced through a heavy interaction between cosmic-ray protons and the dense ISM in the southwestern shell. We also find that the H2 and [FeII] line emissions show an anti-correlated spatial distribution in the same region, suggesting the presence of the clumpy ISM. Such a clumpy morphology of the ISM around IC443 may assist cosmic-ray protons to efficiently interact with large amounts of the ISM protons.
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