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

First results from the most secure multiband sample from the far-ultraviolet to the far-infrared

¹ Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464–8601, Japan e-mail: takeuchi@iar.nagoya-u.ac.jp
² Laboratoire d'Astrophysique de Marseille, OAMP, Université Aix-Marseille, CNRS, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France e-mail: [veronique.buat;elodie.giovannoli;denis.burgarella]@oamp.fr
³ Department of Physics & Astronomy, The Johns Hopkins University, 3701 San Martin Drive, Baltimore, MD 21218, USA e-mail: sebastien@pha.jhu.edu
⁴ Division of Particle and Astrophysical Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464–8602, Japan e-mail: [yuan.fangting;murata.katsuhiro]@g.mbox.nagoya-u.ac.jp
⁵ Instituto de Astrofísica de Andalucía (IAA, CSIC), Camino Bajo de Huétor 50, 18008 Granada, Spain e-mail: jiglesia@iaa.es

Received: 15 October 2009
Accepted: 21 December 2009

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 10⁶ to 10¹² , with a peak at 10¹⁰ . 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 M_r - 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 L_TIR. The luminosity related to the SF activity (L_SF) is dominated by L_TIR even if we take into account the FIR emission from dust heated by old stars. At a high SF rate (SFR) (>20  yr^-1), the fraction of the directly visible SFR, SFR_FUV, decreases. We also estimated the FUV attenuation A_FUV from the FUV-to-TIR luminosity ratio. We examined the L_TIR/L_FUV-UV slope (FUV – NUV) relation. The majority of the sample has L_TIR/L_FUV 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 L_TIR/L_FUV ratios. We found the attenuation indicator L_TIR/L_FUV correlated to the stellar mass of galaxies, , but not with a specific SFR, SFR/.

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.