Cosmic evolution of the [C II]-to-dense neutral gas relation
Year: 2026
Type: article
Abstract: The [C II ] 158 µm line is widely used to trace star formation and the gas contents of high-redshift galaxies. However, it remains unclear under which physical conditions it reliably traces the molecular reservoir, and whether a unique conversion factor α [C II ] can be applied across cosmic time. We investigated the evolution of the relation between the [C II ] luminosity and dense neutral gas mass from z ≃ 10 to z ≃ 0.2 using the V INTERGATAN simulation, a high-resolution cosmological zoom-in of a Milky Way–like galaxy. We post-processed the snapshots with the S KIRT radiative transfer code to generate synthetic [C II ] data cubes. We measured global and spatially resolved (100 pc) relations between [C II ] luminosity ( L [C II ] ), star formation rate (SFR), and dense neutral gas mass ( M DN ). We followed the redshift evolution of the [C II ]–to-dense neutral gas conversion factor α [C II ] , and linked these trends to the evolution of the interstellar medium (ISM) phases. The global L [C II ] – M DN and L [C II ] –SFR relations evolve from a steep, [C II ]-deficient regime at a very low metallicity to an almost linear behaviour, similar to calibrations at z ≈ 2, once the ISM reaches Z gas ≳ 0.05–0.1 Z ⊙ at z ≲ 5. Over this evolution, α [C II ] spans nearly three orders of magnitude, from ≳10 4 down to ≈10 M ⊙ L ⊙ −1 , even though the [C II ] emission remains spatially correlated with the dense neutral gas. We provide prescriptions for α [C II ] based on integrated and local quantities. The latter recovers the dense neutral mass of V INTERGATAN within factors of the of order unity, whereas global relations depending only on L [C II ] and/or the integrated metallicity fail by up to an order of magnitude during major and minor merger epochs. A unique, redshift-independent α [C II ] therefore cannot recover dense neutral gas masses across the regimes we explored. [C II ] remains a viable tracer of dense neutral gas at very high redshifts, but only when used with conversion factors that explicitly account for metallicity, ISM phase mix, and merger events.
Source: Astronomy and Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Awards: G164444715, G1800105685, G1949054838, Par-delà les frontières, l'Université de Strasbourg, G2255650664, The origins disk galaxies in the early Universe, G2694206344, Façonner les talents en formation et en recherche à l'Université de Strasbourg, G3357951378, G399734812, ALICE and ATLAS, G458729750, G471331628, G4779185514, G5296751580, G6136357505, G6276897512, G6285136898, G6389594462, G7240651115, ARRAKIHS - Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys
OpenAlex ID: W7155174497