Physical nature of the [S II]-bright shell nebulae N70 and N185

Ning Xiao Zhang, You Hua Chu, R. M. Williams, Bing Jiang, Yang Chen, R. A. Gruendl

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N70 and N185 are two large (≥100 pc in diameter) shell nebulae in the Large Magellanic Cloud (LMC). Their high [S II]/Hα ratios rival those of supernova remnants (SNRs), but they are not confirmed as SNRs. To study their physical nature, we have obtained XMM-Newton X-ray observations and high-dispersion long-slit echelle spectroscopic observations of these two nebulae. The X-ray spectra of both nebulae can be well interpreted with an optically thin thermal (∼0.2 keV) plasma with the average LMC abundance in a collisional ionization equilibrium. N70 encompasses the OB association LH114. Although N70 has a modest expansion velocity and essentially thermal radio emission, its diffuse X-ray luminosity (∼6.1 × 1035 erg s-1) is higher than that from a quiescent superbubble with N70's density, size, and expansion velocity; thus, N70 is most likely a superbubble that is recently energized by an interior SNR. N185 does not contain any known OB association, and its X-ray luminosity is an order of magnitude lower than expected if it is a quiescent superbubble. N185 has nonthermal radio emission and has high-velocity material expanding at nearly 200 km s-1, similar to many known SNRs in the LMC. Its X-ray luminosity (∼1.9 × 1035 erg s-1) is also consistent with that of an evolved SNR. We therefore suggest that N185 is energized by a recent supernova.

Original languageEnglish (US)
Article number58
JournalAstrophysical Journal
Issue number1
StatePublished - Sep 1 2014


  • ISM
  • bubbles ISM
  • lines and bands ISM
  • supernova remnants X-rays

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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