Based on the photometric data from the Spitzer /SAGE survey and with red giants as the extinction tracers , the mid-infrared ( MIR ) extinction laws in the Large Magellanic Cloud ( LMC ) are derived for the first time in the form of A _ { \lambda } / A _ { { K _ { S } } } , the extinction in the four IRAC bands ( i.e. , [ 3.6 ] , [ 4.5 ] , [ 5.8 ] and [ 8.0 ] { \mu m } ) relative to the 2MASS { K _ { S } } band at 2.16 { \mu m } .
We obtain the near-infrared ( NIR ) extinction coefficient to be E ( { J } - { H } ) / E ( { H } - { K _ { S } } ) \approx 1.29 \pm 0.04 and E ( { J } - { K _ { S } } ) / E ( { H } - { K _ { S } } ) \approx 1.94 \pm 0.04 .
The wavelength dependence of the MIR extinction A _ { \lambda } / A _ { K _ { S } } in the LMC varies from one sightline to another .
The overall mean MIR extinction is A _ { [ 3.6 ] } / A _ { K _ { S } } \approx 0.72 \pm 0.03 , A _ { [ 4.5 ] } / A _ { K _ { S } } \approx 0.94 \pm 0.03 , A _ { [ 5.8 ] } / A _ { K _ { S } } \approx 0.58 \pm 0.04 , and A _ { [ 8.0 ] } / A _ { K _ { S } } \approx 0.62 \pm 0.05 .
Except for the extinction in the IRAC [ 4.5 ] band which may be contaminated by the 4.6 { \mu m } CO gas absorption of red giants ( which are used to trace the LMC extinction ) , the extinction in the other three IRAC bands show a flat curve , close to the Milky Way R _ { V } = 5.5 model extinction curve ( where R _ { V } is the optical total-to-selective extinction ratio ) .
The possible systematic bias caused by the correlated uncertainties of { K _ { S } } - \lambda and { J } - { K _ { S } } is explored in terms of Monte-Carlo simulations .
It is found that this could lead to an overestimation of A _ { \lambda } / A _ { K _ { S } } in the MIR .