AKARI and Spitzer infrared diagnostics of luminous infrared galaxies

MIRABEL IF

Washington

Congreso; AAS Meeting 217, 335,41; 2011

American Astronomical Society

We present AKARI near-infrared (NIR) and Spitzer mid-infrared (MIR) spectroscopy of both luminous infrared galaxies (LIRGs) and ultra luminous infrared galaxies (ULIRGs) from the Revised Bright Galaxy Sample and the 1 Jy sample, respectively. Luminous infrared galaxies emit more of their bolometric luminosity in the infrared (8-1000 microns) than in all other parts of the spectrum combined. It appears that the infrared luminosity originates from a combination of starburst and active galactic nucleus (AGN) (cf. Sanders & Mirabel 1996 and references therein). For the first time we combine emission line fluxes in both 2.5-5 micron data from AKARI with 5-35 micron data from Spitzer to derive new infrared diagnostic diagrams that can distinguish between starburst and AGN activity in heavily obscured (U)LIRGs. Previous attempts at classifying these galaxies in the optical regime have proven to be very difficult due to the heavy dust extinction from buried AGNs. However since infrared radiation is affected much less by dust than in the optical, we show that the infrared emission line diagnostic [Ne III]/[Ne II] vs. [O IV]/Br-alpha appears most promising in separating starburst-driven ULIRGs and AGN-driven ULIRGs. In addition the diagnostic [Ne III]/[Ne II] vs. [S III]/Br-alpha also appears to be moderately effective in separating ULIRGs driven by starbursts and AGNs, while the [NeIII]/[Ne II] vs. [S IV]/Br-alpha ratio does a relatively poor job. These results were then compared to theoretical models generated by the Starburst99 and Mappings codes.