A multi-wavelength study of N63A: A supernova remnant within an H II region in the Large Magellanic Cloud.

Abstract

The nature and physical environments of SNRs are diverse, and for this reason, the understanding of the properties of nearby SNRs is useful in interpreting the emission from SNRs in remote galaxies where we cannot resolve them. In this regard, the LMC is a unique place to study SNRs due to its proximity, location, and composition compared with our galaxy.

We carried out a multi-wavelength study of SNR N63A in the LMC, a young remnant of the SN explosion of one of the most massive (> 40 M_sun) stars in a cluster. It is currently expanding within a large H II region formed by OB stars in the cluster and engulfing a molecular cloud.

First, we aimed to study the overall structure of N63A using NIR imaging and spectroscopic observations of SNR N63A. In the [Fe II] images we detected a two-lobed structure, which has a good spatial correlation with the shock-heated lobes of N63A's optical nebula. We have detected several [Fe II] lines as well as He I, H I and [P II] lines from the emitting region. This allows us to estimate the electron density (~ 4700 cm^3) and a smaller extinction (Av ~ 0.5 mag). We also estimate the pre-shock number density of ~ 30 cm^3 assuming a shock speed of 100 km/s in the [Fe II] emitting region of the SNR.

Second, we present the results of a study of the molecular gas associated with the SNR N63A. We use SEST 12CO J = 1–0 and 2–1 observations, which provide evidence in support of the existence of physical interaction between the SN shocks and the adjoining molecular clouds. We reported a mass of ~ 1.2 x 10^3 M_sun, which is almost three times larger than the previous mass reported using X-ray observations, and a hydrogen column density of N_H ~ 1.4 x 10^21 cm^{-2}, which is 4 times smaller than the total column density derived using our NIR observations, for the cloud which is interacting with the SNR N63A.

We also present detection of shocked H_2 emission in NIR and MIR using the Spitzer IRS observations. The H_2 excitation diagram shows a best-fit with a two-temperature LTE model with the temperatures of 200-300 K and 700-900 K. Comparison of H_2 emission with shock models shows that slow C-shock models fit well to the warm component.

In addition to the [Fe II] features, we also detected H_2-2.12 µm emission from a region with spatial correlation with the [Fe II] emitting region. Although the molecular and ionic shocks arise from the same region, we interpret that Fe II and H_2 emission are tracing independent shocks in N63A based on their properties.

Finally, we studied the environment of SNR N63A in order to investigate its interaction with its ambient medium. We found a half ring-like structure with an average brightness of ~ 2 x 10^{-5} erg cm^{-2} s^{-1} sr^{-1} in Hα, at a distance of 11 - 19 pc from the center of the SNR. This structure can corresponds to circumstellar material produced by the mass loss of the N63s progenitor or by the neighboring OB stars. Another possibility is that this structure is part of the ISM and it is not related to the SNR.