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

Abstract

We aim at constraining the dust mass in high-redshift ($z\gtrsim 5$) galaxies using the upper limits obtained by 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 $M_{\mathrm{d}}\lesssim 2\times 10^6$ M${}_{\odot }$, and the dust mass produced per supernova (SN) $m_{\mathrm{d},\mathrm{SN}}\lesssim 0.1$ M${}_{\odot }$. Such a low $m_{\mathrm{d},\mathrm{SN}}$ 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 $M_{\mathrm{d}}\sim 2\times 10^7$ M${}_{\odot }$ and $m_{\mathrm{d},\mathrm{SN}}\sim 0.3$ M${}_{\odot }$.} 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 $M_{\mathrm{d}}\lesssim 2\times 10^6$ M${}_{\odot }$ for a typical LBG at $z>5$, but this only puts an upper limit for $m_{\mathrm{d},\mathrm{SN}}$ as $\sim 2$ M${}_{\odot }$. This clarifies the importance of observing UV-bright objects (like Himiko) to constrain the dust production by SNe.

12 pages, 6 figures, accepted for publication in MNRAS