Star formation and dust extinction properties of local galaxies from the AKARI-GALEX all-sky surveys

Abstract

Aims. We explore spectral energy distributions (SEDs), star formation (SF), and dust extinction properties of galaxies in the Local Universe. Methods. The AKARI all-sky survey provided the first bright point source catalog detected at 90 μm. Beginning with this catalog, we selected galaxies by matching the AKARI sources with those in the IRAS point source catalog redshift survey. We measured the total GALEX FUV and NUV flux densities with a photometry software we specifically developed for this purpose. In a further step we matched this sample with the Sloan digital sky survey (SDSS) and 2 micron all sky survey (2MASS) galaxies. With this procedure we obtained a basic sample which consists of 776 galaxies. After removing objects whose photometry was contaminated by foreground sources (mainly in the SDSS), we defined the "secure sample" which contains 607 galaxies. Results. The sample galaxies have redshifts of ≲0.15, and their 90-μm luminosities range from 10 6 to 1012 L⊙, with a peak at 10 10 $L-\odot$. The SEDs display a large variety, especially more than four orders of magnitude at the mid-far-infrared (M-FIR), but if we sort the sample with respect to 90 μm, the average SED shows a coherent trend: the more luminous an SED at 90 μm, the redder the global SED becomes. The Mr-NUV-r color-magnitude relation of our sample does not show bimodality, and the distribution is centered on the green valley. We established formulae to convert the FIR luminosity from the AKARI bands to the total IR (TIR) luminosity LTIR. The luminosity related to the SF activity (LSF) is dominated by LTIR even if we take into account the FIR emission from dust heated by old stars. At a high SF rate (SFR) (>20 M⊙ yr-1), the fraction of the directly visible SFR, SFRFUV, decreases. We also estimated the FUV attenuation A FUV from the FUV-to-TIR luminosity ratio. We examined the L TIR/LFUV-UV slope (FUV-NUV) relation. The majority of the sample has LTIR/LFUV ratios five to ten times lower than expected from the local starburst relation, while some luminous IR and all the ultraluminous IR galaxies of this sample have higher LTIR/L FUV ratios. We found the attenuation indicator LTIR/L FUV correlated to the stellar mass of galaxies, M*, but not with a specific SFR, SFR/$M*. Conclusions. Together, these results show that the AKARI survey gives a representative sample of the local SF galaxies which will be a comprehensive local standard of their various properties to be compared with, for instance, high-z SF galaxies. © ESO, 2010.