The ISO 170 µm luminosity function of galaxies

Abstract

We constructed a local luminosity function (LF) of galaxies using a flux-limited sample (S₁₇₀ ≥ 0.195~Jy) of 55 galaxies at z < 0.3 taken from the <sl>ISO</sl> FIRBACK survey at 170 μm. The overall shape of the 170-μm LF is found to be different from that of the total 60-μm LF (Takeuchi et al. 2003): the bright end of the LF declines more steeply than that of the 60-μm LF. This behavior is quantitatively similar to the LF of the cool subsample of the <sl>IRAS</sl> PSCz galaxies. We also estimated the strength of the evolution of the LF by assuming the pure luminosity evolution (PLE): L(z) ∝ (1+z)^Q. We obtained Q=5.0^+2.5_-0.5 which is similar to the value obtained by recent <sl>Spitzer</sl> observations, in spite of the limited sample size. Then, integrating over the 170-μm LF, we obtained the local luminosity density at 170 μm, ρ_L(170 μm). A direct integration of the LF gives ρ_L(170 μm) = 1.1 × 10⁸ h L_⊙ Mpc^-3, whilst if we assume a strong PLE with Q=5, the value is 5.2 × 10⁷ h L_⊙ Mpc^-3. This is a considerable contribution to the local FIR luminosity density. By summing up with other available infrared data, we obtained the total dust luminosity density in the Local Universe, ρ_L(dust)=1.1 × 10⁸h L_⊙ Mpc^-3. Using this value, we estimated the cosmic star formation rate (SFR) density hidden by dust in the Local Universe. We obtained ρ_SFR(dust) ≃ 1.1--1.2 h × 10^-2 M_⊙ yr^-1 Mpc^-3, which means that 59% of the star formation is obscured by dust in the Local Universe.