Expected Sub-mm Emission and Dust Properties of Lyman Break Galaxies at High Redshift

Abstract

We investigate expected sub-mm emission and dust properties of the Lyman Break Galaxies (LBGs) in the Hubble Deep Field (HDF). The SCUBA Deep Survey (Hughes et al., 1998) provides an upper limit of the 850 micron flux densities of the LBGs. With this constraint, we argue that a typical ultra-violet to far-infrared spectral shape of the high-redshift LBGs is rather close to a template spectrum of low-reddening starburst galaxies in the local universe but different from that of heavily dust-enshrouded ultra-luminous far-infrared galaxies like Arp220. We also evaluate the lower-limit temperature of dust in LBGs assuming single- and two-component modified black-body spectrum. To estimate the total amount of energy re-emitted in FIR wavelength, we take two different approaches; model fitting of the UV spectra of LBGs and an empirical method using the relationship between UV spectral shape and UV/FIR flux ratio observed for local starburst galaxies. Both methods give lower-limit temperature of the LBGs as around 40 K, which is higher than the typical dust temperature of local optical- and infrared-selected galaxies. This result is also supported by the comparison of the expected sub-mm flux of the LBGs with the cosmic FIR background radiation. The high dust temperature may indicate the effective massive-star formation or different dust properties in the high-redshift LBGs.