[NII] fine-structure emission at 122 and 205um in a galaxy at z=2.6: a globally dense star-forming interstellar medium

Abstract

We present new observations with the Atacama Large Millimeter/sub-millimeter Array of the 122um and 205um fine-structure line emission of singly-ionised nitrogen in a strongly lensed starburst galaxy at z=2.6. The 122/205um [NII] line ratio is sensitive to electron density, n_e, in the ionised interstellar medium, and we use this to measure n_e~300cm^-3 averaged across the galaxy. This is over an order of magnitude higher than the Milky Way average, but comparable to localised Galactic star-forming regions. Combined with observations of the atomic carbon (CI(1-0)) and carbon monoxide (CO(4-3)) in the same system, we reveal the conditions in this intensely star-forming system. The majority of the molecular interstellar medium has been driven to high density, and the resultant conflagration of star formation produces a correspondingly dense ionised phase, presumably co-located with myriad HII regions that litter the gas-rich disk.

9 pages, 4 figures. Accepted for publication in ApJ

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Cited by in corpus (4)

• MIRI/JWST observations reveal an extremely obscured starburst in the z=6.9 system SPT0311-58
• Ammonia in the interstellar medium of a starbursting disc at z=2.6
• The [NII] 205 $\mu$m line emission from high-z SMGs and QSOs
• Massive molecular gas reservoir in a luminous sub-millimeter galaxy during cosmic noon