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Luminosity functions of local infrared galaxies with AKARI: implications for the cosmic star formation history and AGN evolution

Authors


E-mail: tomo@ifa.hawaii.edu

ABSTRACT

Infrared (IR) luminosity is fundamental to understanding the cosmic star formation history and active galactic nuclei (AGN) evolution, since their most intense stages are often obscured by dust. However, local IR luminosity function estimates today are still based on the IRAS survey in the 1980s, with wavelength coverage only up to 100 μm. The AKARI IR space telescope performed an all-sky survey in six IR bands (9, 18, 65, 90, 140 and 160 μm) with 3–10 times better sensitivity, covering the crucial far-IR wavelengths across the peak of the dust emission. Combined with a better spatial resolution, AKARI can much more precisely measure the total infrared luminosity (LTIR) of individual galaxies, and thus, the total infrared luminosity density in the local Universe.

By fitting modern IR spectral energy distribution (SED) models, we have remeasured LTIR of the IRAS Revised Bright Galaxy Sample, which is a complete sample of local galaxies with S60 μm > 5.24 Jy.

We present mid-IR monochromatic luminosity Lν) to LTIR correlations for Spitzer8 μm, AKARI9 μm, IRAS12 μm, WISE12 μm, ISO15 μm, AKARI18 μm, WISE22 μm and Spitzer24 μm filters. These measures of LMIR are well correlated with LTIR, with scatter in the range 13–44 per cent. The best-fitting LMIR-to-LTIR conversions provide us with estimates of LTIR using only a single MIR band, in which several deep all-sky surveys are becoming available such as AKARI MIR and WISE.

Although we have found some overestimates of LTIR by IRAS due to contaminating cirrus/sources, the resulting AKARI IR luminosity function (LF) agrees well with that from IRAS. We integrate the LF weighted by LTIR to obtain a cosmic IR luminosity density of ΩTIR= (8.5+1.5−2.3) × 107  L Mpc−3, of which 7 ± 1 per cent is produced by luminous infrared galaxies (LIRGs) (LTIR > 1011  L), and only 0.4 ± 0.1 per cent is from ultraluminous infrared galaxies (ULIRGs) (LTIR > 1012  L) in the local Universe, in stark contrast to high-redshift results.

We separate the contributions from AGN and star-forming galaxies (SFGs). The SFG IR LF shows a steep decline at the bright end. Combined with high-redshift results from the AKARI NEP deep survey, these data show a strong evolution of ΩSFTIR (1 +z)4.0±0.5 and ΩAGNTIR (1 +z)4.4±0.4. For ΩAGNTIR, the ULIRG contribution exceeds that from LIRGs already by z∼ 1. A rapid evolution in both ΩAGNTIR and ΩSFGTIR suggests the correlation between star formation and black hole accretion rate continues up to higher redshifts. We compare the evolution of ΩAGNTIR to that of X-ray luminosity density. The ΩAGNTIRX-rayAGN ratio shows a possible increase at z > 1, suggesting an increase of obscured AGN at z > 1.

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