Abstract
The aim of this work is to characterize physical properties of Ultra Luminous Infrared Galaxies (ULIRGs) and Luminous Infrared Galaxies (LIRGs) detected in the far-infrared (FIR) 90um band in the AKARI Deep Field-South (ADF-S) survey. In particular, we want to estimate the AGN contribution to the [U]LIRGs' infrared emission and which types of AGNs are related to their activity. We examined 69 galaxies at z>0.05 detected at 90um by the AKARI satellite in the ADF-S, with optical counterparts and spectral coverage from the ultraviolet to the FIR. We used two independent spectral energy distribution fitting codes: one fitting the SED from FIR to FUV (CIGALE) and gray-body + power spectrum fit for the infrared part of the spectra (CMCIRSED) in order to identify a subsample of [U]LIRGs, and to estimate their properties. Based on the CIGALE SED fitting, we have found that [U]LIRGs selected at the 90um AKARI band compose ~56% of our sample (we found 17 ULIRGs and 22 LIRGs, spanning over the redshift range 0.06<z<1.23). Their physical parameters, such as stellar mass, star formation rate (SFR), and specific SFR are consistent with the ones found for other samples selected at IR wavelengths. We have detected a significant AGN contribution to the MIR luminosity for 63% of LIRGs and ULIRGs. Our LIRGs contain Type 1, Type 2, and intermediate types of AGN, whereas for ULIRGs, a majority (more than 50%) of AGN emission originates from Type 2 AGNs. The temperature--luminosity and temperature--mass relations for the dust component of ADF--S LIRGs and ULIRGs indicate that these relations are shaped by the dust mass and not by the increased dust heating. We conclude that LIRGs contain Type 1, Type 2, and intermediate types of AGNs, with an AGN contribution to the MIR emission at the median level of 13+/-3%, whereas the majority of ULIRGs contain Type 2 AGNs, with a median AGN fraction equal to 19+/-8%.
Highlights
The first infrared all-sky survey performed by the satellite The Infra-Red Astronomical Satellite (IRAS, Soifer et al 1987; Neugebauer et al 1984) in the early 1980s established the existence of galaxies emitting very brightly in infrared (IR) wavelengths with total IR luminosities greater than 1012 [L ]
In this paper we present a sample of 39 luminous infrared galaxies (LIRGs) and ultra luminous infrared galaxies (ULIRGs) selected from one of the deep surveys created by the infrared Japanese satellite named AKARI (Murakami et al 2007)
Star formation history The SFHs used by Code Investigating GALaxy Emission (CIGALE) are: (1) the double decreasing exponential star-formation history module, which implements a SFH composed of two decreasing exponentials; (2) the delayed tau model, which implements a SFH described as a delayed rise of the star formation rate (SFR) up to a maximum, followed by an exponential decrease; and the (3) custom module, which can be read from the file
Summary
The first infrared all-sky survey performed by the satellite The Infra-Red Astronomical Satellite (IRAS, Soifer et al 1987; Neugebauer et al 1984) in the early 1980s established the existence of galaxies emitting very brightly in infrared (IR) wavelengths with total IR luminosities greater than 1012 [L ]. The scatter for a low zspec sample, visible, can induce a large error in the luminosity distance (DL), and cause possible inaccuracy of our analysis To avoid this problem, we rejected all objects with spectroscopic or photometric redshift
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