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

TL;DR

This study uses high-resolution X-ray imaging to reveal shock-heated hot gas in NGC 6240, linking it to starburst activity and large-scale gas morphology, providing insights into galaxy merger dynamics.

Contribution

First detailed spatial mapping of hot, shock-heated gas in NGC 6240, connecting X-ray emission to starburst-driven shocks and galaxy merger processes.

Findings

Detected 70 million K hot gas over 5 kpc scale.

Found spatial correlation between hot gas and H_2, H extalphailaments.

Hot gas luminosity exceeds that of typical starburst galaxy M82.

Abstract

We have obtained a deep, sub-arcsecond 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 million K) hot gas over a spatial scale of 5 kpc, indicating the presence of fast shocks with velocity of ~2200 km/s. For the first time we obtain the spatial distribution of this highly ionized gas emitting FeXXV, which shows a remarkable correspondence to the large scale morphology of H_2(1-0) S(1) line emission and H\alpha filaments. Propagation of fast shocks originated in the starburst driven wind into the ambient dense gas can account for this morphological correspondence. With an observed L(0.5-8 keV)=5.3E+41 erg/s, 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}=1.8E+8 Msun) and thermal energy (E_{th}=6.5E+57 ergs). The total iron mass in the highly ionized plasma is M_{Fe}=4.6E+5 Msun. 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.