AKARI IRC 2.5-5 mu m SPECTROSCOPY OF INFRARED GALAXIES OVER A WIDE LUMINOSITY RANGE

作者：Ichikawa Kohei^*; Imanishi Masatoshi; Ueda Yoshihiro; Nakagawa Takao; Shirahata Mai; Kaneda Hidehiro; Oyabu Shinki

来源：Astrophysical Journal, 2014, 794(2): 139.

DOI：10.1088/0004-637X/794/2/139

• galaxies: active
• galaxies: nuclei
• infrared: galaxies

We present the result of a systematic infrared 2.5-5 mu m spectroscopic study of 22 nearby infrared galaxies over a wide infrared luminosity range (10(10) L-circle dot < L-IR < 10(13) L-circle dot) obtained from the AKARI Infrared Camera (IRC). The unique band of the AKARI IRC spectroscopy enables us to access both the 3.3 mu m polycyclic aromatic hydrocarbon (PAH) emission feature from star-forming activity and the continuum of torus-dust emission heated by an active galactic nucleus (AGN). Applying our AGN diagnostics to the AKARI spectra, we discover 14 buried AGNs. The large fraction of buried AGNs suggests that AGN activity behind the dust is almost ubiquitous in ultra-/luminous infrared galaxies (U/LIRGs). We also find that both the fraction and energy contribution of buried AGNs increase with infrared luminosity from 10(10) L-circle dot to 10(13) L-circle dot, including normal infrared galaxies with L-IR < 10(11) L-circle dot. The energy contribution from AGNs in the total infrared luminosity is only similar to 7% in LIRGs and similar to 20% in ULIRGs, suggesting that the majority of the infrared luminosity originates from starburst activity. Using the PAH emission, we investigate the luminosity relation between star formation and AGNs. We find that these infrared galaxies exhibit higher star formation rates than optically selected Seyfert galaxies with the same AGN luminosities, implying that infrared galaxies could be an early evolutionary phase of AGN.

• 出版日期2014-10-20
• 单位中国科学院国家天文台