Radio properties of nearby ultraluminous infrared galaxies with luminous buried active galactic nuclei signatures.

We present the results of our multifrequency observations for 10 ultraluminous infrared galaxies (ULIRGs) made by the Karl G. Jansky Very Large Array at 1.4, 5.5, 9.0, and 14.0 GHz. Our sample was selected from ULIRGs whose active galactic nuclei (AGNs) are not found at optical (~70% of the entire ULIRGs), but whose presence is suggested at mid-infrared or submillimetre (>50% of the non-AGN ULIRGs at optical). The statistical properties of the targets are similar to those of the entire ULIRG sample, which implies that ULIRGs have common radiative processes regardless of the presence of optical AGNs, and thus AGNs might equally contribute to the radio emissions of every ULIRG. Although their spectra are mainly explained by starburst, some individual sources suggest contributions from AGNs. IRAS 00091-0738, IRAS 00188-0856, and IRAS 01298-0744 show spectral breaks at high frequencies, which can be explained by synchrotron aging of nonthermal plasma emitted from AGNs. In addition, we found 100-kpc scale extended emission associated with IRAS 01004-2237. The two-sided morphology and absence of extended X-ray emission suggest that this system is not induced by a merger in a cluster but originates from AGN activity.