Gas and star formation from HD and dust emission in a strongly lensed galaxy. Issue 3 (7th September 2020)

• Record Type: Journal Article
• Authors: Jones, G C; Maiolino, R; Caselli, P; Carniani, S
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 498:Issue 3(2020)
• Page Start: 4109
• Page End: 4118
• Publication Date: 2020-09-07
• Subjects: ISM: molecules -- galaxies: high-redshift -- galaxies: starburst; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa2689
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: The molecular gas content of high-redshift galaxies is a highly sought-after property. However, H2 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 $\rm M_{H_2}\lt 6.4\times 10^{11}\, M_{\odot }$ . This is used to find a limit on the $L^{\prime }_{\mathrm{ CO}}$ conversion factor of $\rm \alpha _{CO}\lt 5.8\, M_{\odot}(K\, km\, s^{-1}\, pc^2)^{-1}$ . 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 Mdust = 10 8.92 ± 0.02 M⊙, dust temperature 78.6 ± 0.5 K, dust emissivity spectral index β = 1.81 ± 0.03, and star formation rate SFR = 3800 ± 100 M⊙ yr −1 . Using the continuum flux densities to estimate the total gas mass of the source, we find $\rm M_{H_2}\lt 2.4\times 10^{11}\, M_{\odot }$ , assuming subsolar metallicity. This implies a CO conversion factor of αCO < 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.