Context :

Aims : We have studied the H II region DEM L299 in the Large Magellanic Cloud ( LMC ) to understand its physical characteristics and morphology in different wavelengths .

Methods : We performed a spectral analysis of archived XMM-Newton EPIC data and studied the morphology of DEM L299 in X-ray , optical , and radio wavelengths .
We used H \alpha , [ S II ] , and [ O III ] data from the Magellanic Cloud Emission Line Survey ( MCELS ) and radio 21 cm line data from the Australia Telescope Compact Array ( ATCA ) and the Parkes telescope as well as radio continuum data ( 3 cm , 6 cm , 20 cm , 36 cm ) from ATCA and from the Molonglo Synthesis Telescope ( MOST ) .

Results : Our morphological studies imply that , in addition to the supernova remnant SNR B0543-68.9 reported in previous studies , a superbubble also overlaps the SNR in projection .
The position of the SNR is clearly defined through the [ S II ] /H \alpha flux ratio image .
Moreover , the optical images show a shell-like structure that is located farther to the north and is filled with diffuse X-ray emission , which again indicates the superbubble .
Radio 21 cm line data show a shell around both objects .
Radio continuum data show diffuse emission at the position of DEM L299 , which appears clearly distinguished from the H ii region LHA 120-N 164 that lies south-west of it .
We determined the spectral index of SNR B0543-68.9 to be \alpha = -0.34 , which indicates the dominance of thermal emission and therefore a rather mature remnant .
We determined the basic properties of the diffuse X-ray emission for the SNR , the superbubble , and a possible blowout region of the bubble , as suggested by the optical and X-ray data .
We obtained an age of ( 8.9 ^ { +9.2 } _ { -5.4 } ) kyr for the SNR and a temperature of ( 0.64 ^ { +0.73 } _ { -0.20 } ) keV for the hot gas inside the SNR , as well as a thermal energy content and temperature of the hot gas inside the superbubble of ( 4.3 ^ { +8.1 } _ { -2.6 } ) \times 10 ^ { 50 } \phi ^ { 0.5 } erg and ( 0.74 ^ { +0.36 } _ { -0.30 } ) keV , with \phi being the gas-filling factor .

Conclusions : We conclude that DEM L299 consists of a superposition of SNR B0543-68.9 and a superbubble , which we identified based on optical data .