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

doi:10.1093/mnrasl/slac111

paper

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

arXiv:2209.09268 · doi:10.1093/mnrasl/slac111

Abstract

We report the detection of the ground state rotational emission of ammonia, ortho-NH $_{3}$ $(J_{K} = 1_{0} \to 0_{0})$ 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 NH $_{3}$ emission is broadly tracing the global molecular reservoir, but likely distributed in pockets of high density ( $n ≳ 5 \times 1 0^{4}$ cm $^{- 3}$ ). With a luminosity of $2.8 \times 1 0^{6}$ $L_{⊙}$ , the NH $_{3}$ emission represents $2.5 \times 1 0^{- 7}$ 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 $L_{N H_{3}} / L_{IR}$ 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.

arXiv comment5 pages, 3 figures, accepted for publication in MNRAS Letters

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

Abstract

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