IR SED and Dust Masses of Sub-solar Metallicity Galaxies at z~2.3
  We present results from ALMA 1.2mm continuum observations of a sample of 27
star-forming galaxies at z=2.1-2.5 from the MOSFIRE Deep Evolution Field
(MOSDEF) survey. These galaxies have gas-phase metallicity and star-formation
rate measurements from Hb, [OIII], Ha, and [NII]. Using stacks of Spitzer,
Herschel, and ALMA photometry (rest-frame ~ 8-400$\mu$m), we examine the IR SED
of high-redshift subsolar metallicity (~0.5 $Z_{\odot}$) LIRGs. We find that
the data agree well with an average SED template of higher luminosity local
low-metallicity dwarf galaxies (reduced $\chi^2$ of 1.8). When compared with
the commonly used templates for solar-metallicity local galaxies or
high-redshift LIRGs and ULIRGs, even in the most favorable case (with reduced
$\chi^2$ of 2.8), the templates are rejected at >98% confidence level. The
broader and hotter IR SED of both the local dwarfs and high-redshift subsolar
metallicity galaxies may result from different grain properties, a clumpy dust
geometry, or a harder/more intense ionizing radiation field that heats the dust
to higher temperatures. The obscured SFR indicated by the FIR emission of the
subsolar metallicity galaxies is only ~ 60% of the total SFR, which is
considerably lower than that of the local LIRGs with ~ 96-97% obscured
fractions. Due to the evolving IR SED shape, the local LIRG templates fit to
mid-IR data can overestimate the Rayleigh-Jeans tail measurements at z~2 by a
factor of 2-20, and these templates underestimate IR luminosities if fit to the
observed ALMA fluxes by >0.4dex. At a given stellar mass or metallicity, dust
masses at z~2.3 are an order of magnitude higher than those at z~0. Given the
predicted molecular gas mass fractions, the observed z~2.3 dust-to-stellar mass
ratios suggest lower dust-to-molecular gas masses than in local galaxies at the
same metallicity.
