Luminosity functions for galaxies and quasars in the Spitzer Wide-area Infrared Extragalactic Legacy Survey

Abstract

We construct rest‐frame luminosity functions (LFs) at 3.6, 4.5, 5.8, 8 and 24 μm over the redshift range 0 < z < 2 for galaxies and 0 < z < 4 for optical quasi‐stellar objects (QSOs), using optical and infrared (IR) data from the Spitzer Wide‐area Infrared Extragalactic (SWIRE) Survey. The 3.6‐ and 4.5‐μm galaxy LFs show evidence for moderate positive luminosity evolution up to z∼ 1.5, consistent with the passive ageing of evolved stellar populations. Their comoving luminosity density was found to evolve passively, gradually increasing out to z∼ 0.5–1 but flattening, or even declining, at higher redshift. Conversely, the 24‐μm galaxy LF, which is more sensitive to obscured star formation and/or active galactic nuclei (AGN) activity, undergoes strong positive evolution, with the derived IR energy density and star formation rate (SFR) density ∝ (1 +z)γ with γ= 4.5+0.7−0.6 and the majority of this evolution occurring since z∼ 1. Optical QSOs, however, show positive luminosity evolution in all bands, out to the highest redshifts (3 < z < 4). Modelling as L*∝ (1 +z)γ gave γ= 1.3+0.1−0.1 at 3.6 μm, γ= 1.0+0.1−0.1 at 4.5 μm and stronger evolution at the longer wavelengths (5.8, 8 and 24 μm), of γ∼ 3. Comparison of the galaxy LFs to predictions from a semi‐analytic model based on cold dark matter (CDM) indicates that an initial mass function (IMF) skewed towards higher mass star formation in bursts compared to locally be preferred. As a result, the currently inferred massive SFRs in distant submm sources may require substantial downwards revision.

Mid- and far-infrared luminosity functions and galaxy evolution from multiwavelengthSpitzerobservations up toz ~ 2.5

“…A comparison can be performed at low redshifts with both the IRAS 25 μm LF ) and the Spitzer results from the First Look Survey (FLS) 24 μm team (Marleau et al 2007). As observed at 8 μm, the LF computed by Babbedge et al (2006) is consistent with our results at 24 μm to z ∼ 1. Above, their values seem to underestimate the present computation.…”

“…This result might confirm the finding of Caputi et al that different ways of estimating the K-correction provide consistent results when deriving the monochromatic IR luminosity functions at high-z. To z ∼ 1, we also find good consistency with the results of Babbedge et al (2006) which were based on the SWIRE survey. However, this results at higher z significantly differ from ours, the LF being much lower.…”

“…Caputi et al (2007) presented the rest-frame 8 μm LF at z ∼ 1 and z ∼ 2, Perez-Gonzalez et al (2005) derived the rest-frame 12 μm LF up to z ∼ 2.5, Le Floc'h et al (2006) obtained the 15 μm LF up to z ∼ 1.2, and Babbedge et al (2006) computed the LF at both 8 and 24 μm up to z ∼2, albeit with uncertainties substantially increasing with redshifts arising from their relying on shallow Spitzer and optical photometry and on purely photometric redshifts. Some authors also tried to compute the evolutionary IR [8−1000 μm] LF.…”

“…Caputi et al (2007) present the rest-frame 8 μm LF of star-forming galaxies in two bins at z ∼ 1 and z ∼ 2. Based on an early reduction of SWIRE EN1 field data and using photometric redshifts based on relatively shallow optical imaging, Babbedge et al (2006) computed the mid-IR (8 and 24 μm) galaxy (AGN1) LF to z ∼ 2 (z ∼ 4; albeit with uncertainties that strongly increase with redshift). Spitzer (Werner et al 2004) studies have also allowed accurate determinations of the local (or low-redshift) LFs at 8 and 24 μm (Huang et al 2007;and Marleau et al 2007;Vaccari et al 2009, in preparation), which provide important data sets for comparison with high-z sources.…”

AGN counts at 15$\mu{\rm m}$

“…These results are now confirmed and extended by the data coming from the Spitzer Space Telescope (e.g. Gruppioni et al 2005;Le Floc'h et al 2005;Pérez-González et al 2005;Babbedge et al 2006;Caputi et al 2007). On the contrary, the evolution of AGN at MIR wavelengths are similar to what has been measured in the optical and X-ray bands for type 1 AGN (AGN1) and even slower for type 2 AGN (Matute et al 2002(Matute et al , 2006.…”