Hubble Space Telescope Observations of Oxygen-Rich Supernova Remnants in the Magellanic Cloud. I. Narrow-Band Imaging of N132D in the LMC

Abstract

view Abstract Citations (56) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hubble Space Telescope Observations of Oxygen-Rich Supernova Remnants in the Magellanic Cloud. I. Narrow-Band Imaging of N132D in the LMC Morse, J. A. ; Blair, W. P. ; Dopita, M. A. ; Hughes, J. P. ; Kirshner, R. P. ; Long, K. S. ; Raymond, J. C. ; Sutherland, R. S. ; Winkler, P. F. Abstract We present Hubble Space Telescope (HST WFPC2 images of the young, oxygen- rich supernova remnant N132D in the Large Magellanic Cloud in the [O III]λ5007, [O II]λ3727 and [S II]λλ6724 emission lines, plus a visible continuum band. The ~0.1" resolution of HST allows us to analyze structure within N132D at scales comparable to ground-based images of nearby remnants such as Cas A. The oxygen-rich filaments (seen in [O III] and [O II] emission) are easily distinguished from shocked circumstellar clouds (seen in all three emission lines). Characteristic knots sizes and filament widths are ~0.2" - 0.5" (~1.5-4 x 10^17^ cm), at least partially resolved in our images. For the first time, we discern ionization structure within the shocked interstellar clouds and filaments, reminiscent of filaments in galactic SNRs that are thought to arise from recent shock/interstellar cloud encounters where the full cooling and recombination zone has not yet formed throughout the structure. Conversely, there appears to be fairly uniform ionization in the O-rich filaments. We also observe highly ionized, diffuse emission extending all the way around the outer edges of the remnant, as previously seen in ground-based studies. We compare our HST optical emission-line images of N132D to the ROSAT HRI soft X-ray image and find that the X-ray emission is closely traced optically by shocked circumstellar clouds; the O-rich filaments do not appear to be emitting X-rays. The limb-brightened X-ray shell aligns remarkably precisely along the inner edge of the diffuse outer rim. The diffuse emission probably represents ambient molecular gas that is being dissociated and photoionized by high-energy photons originating in the fast SNR shocks. We have used the MAPPINGS II code to model the X-ray producing main blast wave as an ~800 km s^-1^ shock moving into a circumstellar medium of density N_0_ ~ 3 cm^-3^. The preshock ISM density of N_0_ ~ 3 cm^-3^ inferred from our shock model agrees with the preshock density estimated from the [O III]λ5007 surface brightness in the diffuse outer rim. We also model the [O III]/[S II] emission-line ratios in the photoionized outer rim as a function of distance ahead of the main blast wave using the radiation field produced by fast shocks in the remnant as the ionizing source. According to our models, the ionizing radiation from the ~800 km s^-1^ main blast wave is not sufficient to generate the observed optical emission from the outer rim precursor. An extra source of EUV photons appears necessary to achieve the observed ionization of the preshock gas. We estimate that EUV photons produced in slower shocks moving into QSF-type clouds around the outer rim can probably contribute enough ionizing photons to achieve the observed ionization. Radiative shocks moving through the O-rich filaments may also be an important source of EUV photons. ======================================================================== 1996AJ....112.2350M Publication: The Astronomical Journal Pub Date: August 1996 DOI: 10.1086/118031 Bibcode: 1996AJ....112..509M Keywords: SUPERNOVA REMNANTS full text sources ADS | data products SIMBAD (8) NED (1) MAST (1) HEASARC (1) ESA (1) Related Materials (2) Part 2: 1996AJ....112.2350M Part 3: 2000ApJ...537..667B