Wang, Junfeng, Nardini, Emanuele, Fabbiano, Giuseppina, Karovska, Margarita, Elvis, Martin, Pellegrini, Silvia, Max, Claire, Risaliti, Guido, U, Vivian, and Zezas, Andreas. 2014. "Fast and Furious: Shock Heated Gas as the Origin of Spatially Resolved Hard X-Ray Emission in the Central 5 kpc of the Galaxy Merger NGC 6240." The Astrophysical Journal 781:55. https://doi.org/10.1088/0004-637X/781/1/55
We have obtained a deep, subarcsecond resolution X-ray image of the nuclear region of the luminous galaxy merger NGC 6240 with Chandra, which resolves the X-ray emission from the pair of active nuclei and the diffuse hot gas in great detail. We detect extended hard X-ray emission from kT ~ 6 keV (~70 MK) hot gas over a spatial scale of 5 kpc, indicating the presence of fast shocks with a velocity of ~2200 km s-1. For the first time, we obtain the spatial distribution of this highly ionized gas emitting Fe XXV, which shows a remarkable correspondence to the large-scale morphology of H2(1-0) S(1) line emission and H? filaments. Propagation of fast shocks originating in the starburst-driven wind into the ambient dense gas can account for this morphological correspondence. With an observed L 0.5-8 keV = 5.3 × 1041 erg s-1, the diffuse hard X-ray emission is ~100 times more luminous than that observed in the classic starburst galaxy M82. Assuming a filling factor of 1% for the 70 MK temperature gas, we estimate its total mass (M hot = 1.8 × 108 M ?) and thermal energy (E th = 6.5 × 1057 erg). The total iron mass in the highly ionized plasma is M Fe = 4.6 × 105 M ?. Both the energetics and the iron mass in the hot gas are consistent with the expected injection from the supernovae explosion during the starburst that is commensurate with its high star formation rate. No evidence for fluorescent Fe I emission is found in the CO filament connecting the two nuclei.