We present a multi-wavelength observational study of the NGC 2024 filament using infrared to sub-millimeter continuum and the { NH _ { 3 } } ( 1 , 1 ) and ( 2 , 2 ) inversion transitions centered on FIR-3 , the most massive core therein .
FIR-3 is found to have no significant infrared point sources in the Spitzer/IRAC bands .
But the { NH _ { 3 } } kinetic temperature map shows a peak value at the core center with T _ { k } = 25 K which is significantly higher than the surrounding level ( T _ { k } = 15 - 19 K ) .
Such internal heating signature without an infrared source suggests an ongoing core collapse possibly at a transition stage from first hydrostatic core ( FHSC ) to protostar .
The eight dense cores in the filament have dust temperatures between 17.5 and 22 K. They are much cooler than the hot ridge ( T _ { d } = 55 K ) around the central heating star IRS-2b .
Comparison with a dust heating model suggests that the filament should have a distance of 3 - 5 pc from IRS-2b .
This value is much larger than the spatial extent of the hot ridge , suggesting that the filament is spatially separated from the hot region along the line of sight .