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Journal Article

Gas and star formation from HD and dust emission in a strongly lensed galaxy


Caselli,  P.
Center for Astrochemical Studies at MPE, MPI for Extraterrestrial Physics, Max Planck Society;

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Jones, G. C., Maiolino, R., Caselli, P., & Carniani, S. (2020). Gas and star formation from HD and dust emission in a strongly lensed galaxy. Monthly Notices of the Royal Astronomical Society, 498(3), 4109-4118. doi:10.1093/mnras/staa2689.

Cite as: https://hdl.handle.net/21.11116/0000-0008-4214-7
The molecular gas content of high-redshift galaxies is a highly sought-after property. However, H<sub>2</sub> is not directly observable in most environments, so its mass is probed through other emission lines (e.g. CO, [C i], [C ii]), or through a gas-to-dust ratio. Each of these methods depends on several assumptions, and are best used in parallel. In this work, we extend an additional molecular gas tracer to high-redshift studies by observing hydrogen deuteride (HD) emission in the strongly lensed z = 5.656 galaxy SPT0346−52 with ALMA. While no HD(1–0) emission is detected, we are able to place an upper limit on the gas mass of M<sub>H<sub>2</sub></sub><6.4×10<sup>11</sup>M<sub>⊙</sub>⁠. This is used to find a limit on the L′<sub>CO</sub> conversion factor of      α<sub>CO</sub><5.8M<sub>⊙</sub>(Kkms<sup>−1</sup>pc<sup>2</sup>)−1⁠. In addition, we construct the most complete spectral energy distribution of this source to date, and fit it with a single-temperature modified blackbody using the nested sampling code multinest, yielding a best-fitting dust mass M<sub>dust</sub> = 10<sup>8.92 ± 0.02</sup> M<sub>⊙</sub>, dust temperature 78.6 ± 0.5 K, dust emissivity spectral index β = 1.81 ± 0.03, and star formation rate SFR = 3800 ± 100 M<sub>⊙</sub> yr<sup>−1</sup>. Using the continuum flux densities to estimate the total gas mass of the source, we find     M<sub>H<sub>2</sub></sub><2.4×10<sup>11</sup>M<sub>⊙</sub> , assuming subsolar metallicity. This implies a CO conversion factor of α<sub>CO</sub> < 2.2, which is between the standard values for MW-like galaxies and starbursts. These properties confirm that SPT0346−52 is a heavily starbursting, gas-rich galaxy.