The ISO 170 μm luminosity function of galaxies

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 ISO 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, Yoshikawa, & Ishii 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 IRAS PSCz galaxies. We also estimated the strength of the evolution of the LF by assuming the pure luminosity evolution (PLE): L(z) ∝ (1 + z). We obtained Q = 5.0 −0.5 which is similar to the value obtained by recent Spitzer observations, in spite of the limited sample size. Then, integrating over the 170-μm LF, we obtained the local luminosity density at 170 μm, ρL(170μm). A direct integration of the LF gives ρL(170μm) = 1.1 × 10 h L⊙Mpc , whilst if we assume a strong PLE with Q = 5, the value is 5.2 × 10h L⊙Mpc . 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, ρL(dust) = 1.1 × 10 h L⊙Mpc . Using this value, we estimated the cosmic star formation rate (SFR) density hidden by dust in the Local Universe. We obtained ρSFR(dust) ≃ 1.1–1.2 h× 10 −2 M⊙ yr Mpc, which means that 58.5 % of the star formation is obscured by dust in the Local Universe.