The dust properties of z ∼ 3 MIPS-LBGs from photochemical models

Abstract

The stacked spectral energy distribution (SED) 24 μm Lyman break galaxies (MIPS-LBGs) detected by the Multiband Imaging Photometer for Spitzer (MIPS) is fitted by means of the spectrophotometric model GRASIL with an "educated" fitting approach which benefits from the results of chemical evolution models. The star formation rate-age-metallicity degeneracies of SED modeling are broken by using star formation history (SFH) and chemical enrichment history suggested by chemical models. The dust mass, dust abundance, and chemical pattern of elements locked in the dust component are also directly provided by chemical models. Using our new "fitting" approach, we derive the total mass Mtot, stellar mass M*, gas mass M g , dust mass Md , age, and star formation rate (SFR) of the stacked MIPS-LBG in a self-consistent way. Our estimate of M* = 8 × 1010 of the stacked MIPS-LBG agrees with other works based on UV-optical SED fitting. We suggest that the MIPS-LBGs at z ∼ 3 are young (0.3-0.6 Gyr), massive (Mtot ∼ 1011 M ⊙), dusty (Md ∼ 108 M ⊙), and metal-rich (Z ∼ Z⊙) progenitors of elliptical galaxies undergoing a strong burst of star formation (SFR ∼ 200 M⊙ yr-1). Our estimate of Md = 7 × 107 M⊙ of the stacked MIPS-LBG is about a factor of eight lower than the estimated value based on single temperature graybody fitting, suggesting that self-consistent SED models are needed to estimate dust mass. By comparing with Milky Way molecular cloud and dust properties, we suggest that denser and dustier environments and flatter dust size distribution are likely in high-redshift massive star-forming galaxies. These dust properties, as well as the different types of SFHs, can cause different SED shapes between high-redshift star-forming ellipticals and local starburst templates. This discrepancy of SED shapes could in turn explain the non-detection at submillimeter wavelengths of IR luminous (L ⊙IR≥1012 L⊙) MIPS-LBGs. © 2013. The American Astronomical Society. All rights reserved..