Evolution of the far-infrared luminosity functions in the Spitzer Wide-area Infrared Extragalactic Legacy Survey

We present new observational determination of the evolution of the rest-frame 70 and 160µm and total infrared (TIR) galaxy luminosity functions (LFs) using 70 and 160µm data from the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy survey. The LFs were constructed for sources with spectroscopic redshifts only in the XMM-LSS and Lockman Hole fields from the SWIRE photometric redshift catalogue. The 70µm and TIR LFs were constructed in the redshift range 0 redshift range 0 redshift. We find that the double power-law model is a better representation of the infrared (IR) LF than the more commonly used power-law and Gaussian model. We model the evolution of the far-IR LFs as a function of redshift where the characteristic luminosity L ∗ evolve as ∝ (1 + z) αL .T he rest-frame 70µm LF shows a strong luminosity evolution out to z = 1.2 with αL = 3.41 +0.18 −0.25 . The rest-frame 160µm LF also showed rapid luminosity evolution with αL = 5.53 +0.28 −0.23 out to z = 0.5. The rate of evolution in luminosity is consistent with values estimated from previous studies using data from IRAS, ISO and Spitzer. The TIR LF evolves in luminosity with αL = 3.82 +0.28 −0.16 which is in agreement with previous results from Spitzer 24µm which find strong luminosity evolution. By integrating the LF we calculated the comoving IR luminosity density out to z = 1.2, which confirms the rapid evolution in number density of luminous IR galaxies which contribute ∼68 +10 −07 per cent to the comoving star formation rate density at z = 1.2. Our results based on 70µm data confirm that the bulk of the star formation at z = 1 takes place in dust-obscured objects.