Ammonia in the interstellar medium of a starbursting disc at z=2.6

M. J. Doherty, J. E. Geach, R. J. Ivison, K. M. Menten, A. M. Jacob, J. Forbrich, S. Dye

Submitted on 19 September 2022


We report the detection of the ground state rotational emission of ammonia, ortho-NH3 (JK=1000) in a gravitationally lensed, intrinsically hyperluminous, star-bursting galaxy at z=2.6. The integrated line profile is consistent with other molecular and atomic emission lines which have resolved kinematics well-modelled by a 5 kpc-diametre rotating disc. This implies that the gas responsible for NH3 emission is broadly tracing the global molecular reservoir, but likely distributed in pockets of high density (n5×104 cm3). With a luminosity of 2.8×106 L, the NH3 emission represents 2.5×107 of the total infrared luminosity of the galaxy, comparable to the ratio observed in the Kleinmann-Low nebula in Orion and consistent with sites of massive star formation in the Milky Way. If LNH3/LIR serves as a proxy for the 'mode' of star formation, this hints that the nature of star formation in extreme starbursts in the early Universe is similar to that of Galactic star-forming regions, with a large fraction of the cold interstellar medium in this state, plausibly driven by a storm of violent disc instabilities in the gas-dominated disc. This supports the 'full of Orions' picture of star formation in the most extreme galaxies seen close to the peak epoch of stellar mass assembly.


Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letters

Subject: Astrophysics - Astrophysics of Galaxies