Dust masses of z > 5 galaxies from SED fitting and ALMA upper limits

We aim at constraining the dust mass in high-z (z ≳ 5) galaxies using the upper limits obtained by Atacama Large Millimetre/submillimetre Array (ALMA) in combination with the rest-frame UV-optical spectral energy distributions (SEDs). For SED fitting, because of degeneracy between dust extinction and stellar age, we focus on two extremes: continuous star formation (Model A) and instantaneous star formation (Model B). We apply these models to Himiko (as a representative UV-bright object) and a composite SED of z > 5 Lyman break galaxies (LBGs). For Himiko, Model A requires a significant dust extinction, which leads to a high dust temperature >70 K for consistency with the ALMA upper limit. This high dust temperature puts a strong upper limit on the total dust mass M_d ≲ 2 × 10⁶ M_⊙, and the dust mass produced per supernova (SN) m_d,SN ≲ 0.1 M_⊙. Such a low m_{d, SN} suggests significant loss of dust by reverse shock destruction or outflow, and implies that SNe are not the dominant source of dust at high z. Model B allows M_d ∼ 2 × 10⁷ M_⊙ and m_d,SN ∼ 0.3 M_⊙. We could distinguish between Models A and B if we observe Himiko at wavelength < 1.2 mm by ALMA. For the LBG sample, we obtain M_d ≲ 2 × 10⁶ M_⊙ for a typical LBG at z > 5, but this only puts an upper limit for m_d,SN as ∼2 M_⊙. This clarifies the importance of observing UV-bright objects (like Himiko) to constrain the dust production by SNe.