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Arxiv: The JWST/NIRSpec view of the nuclear region in the prototypical merging galaxy NGC 6240 Published: 12/19/2024 11:37:36 AM Updated: 2/7/2025 1:04:15 PM

Paper abstract: Merger events are thought to be an important phase in the assembly of massivegalaxies. At the same time, Active Galactic Nuclei (AGN) play a fundamentalrole in the evolution of their star formation histories. Both phenomena can beobserved at work in NGC 6240, a local prototypical merger, classified as anUltraLuminous InfraRed Galaxy (ULIRG) thanks to its elevated infraredluminosity. Interestingly, NGC 6240 hosts two AGN separated by 1.5''(~ 735 pc),detected in both X-ray and radio band. Taking advantage of the unprecedentedsensitivity and wavelength coverage provided by the Integral Field Unit (IFU)of the NIRSpec instrument onboard JWST, we observed the nuclear region of NGC6240 in a FoV of 3.7'' x 3.7''(1.9 x 1.9 kpc^2), to investigate gas kinematicsand InterStellar Medium (ISM) properties with a high spatial resolution of ~0.1'' (or ~ 50 pc). We separated the different gas kinematic components throughmulti-Gaussian fitting and studied the excitation properties of the ISM fromthe NIR diagnostic diagram based on the H_2 1-0 S(1)/BrGamma and [FeII]1.257micron/PaBeta lines ratios. We isolated the ionization cones of the twonuclei, and detected coronal lines emission from both of them. Using H_2 lineratios, we found that the molecular hydrogen gas is excited mostly by thermalprocesses. We computed a hot molecular gas mass of 1.3 x 10^5 M_sun and anionized gas mass in the range of 10^5 - 10^7 M_sun. We studied withunprecedented spatial resolution and sensitivity the kinematics of themolecular and ionized gas phases. We revealed the complex structure of themolecular gas and found a blueshifted outflow near the Southern nucleus,together with filaments connecting a highly redshifted H_2 cloud with the twonuclei. We speculate on the possible nature of this H_2 cloud and propose twopossible scenarios: either outflowing gas, or a tidal cloud falling onto thenuclei.