Article,
A high-redshift calibration of the [O I]-to-H I conversion factor in star-forming galaxies
Contributors
Heintz, Kasper Elm
0000-0002-9389-7413
(Corresponding author)
[1]
Jakobsson, Pall P
0000-0002-9404-5650
[2]
Madden, Suzanne C
0000-0003-3229-2899
[3]
Watson, Darach Jafar
0000-0002-4465-8264
[1]
Magdis, Georgios E
0000-0002-4872-2294
[1]
[4]
Valentino, Francesco M
0000-0001-6477-4011
[1]
[5]
Greve, Thomas R
0000-0002-2554-1837
[1]
[4]
Vizgan, David
0000-0001-7610-5544
[6]
Affiliations
- [1] University of Copenhagen [NORA names: KU University of Copenhagen; University; Denmark; Europe, EU; Nordic; OECD];
- [2] University of Iceland [NORA names: Iceland; Europe, Non-EU; Nordic; OECD];
- [3] Astrophysique, Instrumentation et Modélisation [NORA names: France; Europe, EU; OECD];
- [4] Technical University of Denmark [NORA names: DTU Technical University of Denmark; University; Denmark; Europe, EU; Nordic; OECD];
- [5] European Southern Observatory [NORA names: Germany; Europe, EU; OECD];
(... more)
Abstract
The assembly and build-up of neutral atomic hydrogen (H I ) in galaxies is one of the most fundamental processes in galaxy formation and evolution. Studying this process directly in the early universe is hindered by the weakness of the hyperfine 21-cm H I line transition, impeding direct detections and measurements of the H I gas masses ( M HI ). Here we present a new method to infer M HI of high-redshift galaxies using neutral, atomic oxygen as a proxy. Specifically, we derive metallicity-dependent conversion factors relating the far-infrared [O I ]-63 μm and [O I ]-145 μm emission line luminosities and M HI in star-forming galaxies at z ≈ 2 − 6 using gamma-ray bursts (GRBs) as probes. We calibrate the [O I ]-to-H I conversion factor relying on a sample of local galaxies with direct measurements of M HI and [O I ]-63 μm and [O I ]-145 μm line luminosities in addition to the S IGAME hydrodynamical simulation framework at similar epochs ( z ≈ 0). We find that the [O I ] 63 μm -to-H I and [O I ] 145 μm -to-H I conversion factors, here denoted β [OI]−63 μm and β [OI]−145 μm , respectively, universally appear to be anti-correlated with the gas-phase metallicity. The GRB measurements further predict a mean ratio of L [OI]−63 μm / L [OI]−145 μm = 1.55 ± 0.12 and reveal generally less excited [C II ] over [O I ] compared to the local galaxy sample. The z ≈ 0 galaxy sample also shows systematically higher β [OI]−63 μm and β [OI]−145 μm conversion factors than the GRB sample, indicating either suppressed [O I ] emission in local galaxies likely due to their lower hydrogen densities or more extended, diffuse H I gas reservoirs traced by the H I 21-cm. Finally, we apply these empirical calibrations to the few detections of [O I ]-63 μm and [O I ]-145 μm line transitions at z ≈ 2 from the literature and further discuss the applicability of these conversion factors to probe the H I gas content in the dense, star-forming interstellar medium (ISM) of galaxies well into the epoch of reionization.
