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 160 μm and total infrared (TIR) galaxy luminosity functions (LFs) using 70 and 160 μm 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 70 μm and TIR LFs were constructed in the redshift range 0 < z < 1.2 and the 160 μm LF was constructed in the redshift range 0 < z < 0.5 using a parametric Bayesian and the 1/V
max
methods. We assume in our models that the faint-end power-law index of the LF does not evolve with 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
$\propto (1+z)^{\alpha _{L}}$
. The rest-frame 70 μm LF shows a strong luminosity evolution out to z = 1.2 with
$\alpha _{L}=3.41^{+0.18}_{-0.25}$
. The rest-frame 160 μm LF also showed rapid luminosity evolution with
$\alpha _{L}=5.53^{+0.28}_{-0.23}$
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
$\alpha _{L}=3.82^{+0.28}_{-0.16}$
which is in agreement with previous results from Spitzer 24 μm 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 70 μm data confirm that the bulk of the star formation at z = 1 takes place in dust-obscured objects.