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We present the results of our ALMA Cycle 0 observations, using HCN/HCO+/HNCJ=4-3 lines, of six nearby luminous infrared galaxies with various energeticcontributions from active galactic nuclei (AGNs) estimated from previousinfrared spectroscopy. These lines are very effective for probing the physicalproperties of high-density molecular gas around the hidden energy sources inthe nuclear regions of these galaxies. We find that HCN to HCO+ J=4-3 fluxratios tend to be higher in AGN-important galaxies than in starburst-dominatedregions, as was seen at the J=1-0 transition, while there is no cleardifference in the HCN-to-HNC J=4-3 flux ratios among observed sources. A galaxywith a starburst-type infrared spectral shape and very large molecular linewidths shows a high HCN-to-HCO+ J=4-3 flux ratio, which could be due toturbulence-induced heating. We propose that enhanced HCN J=4-3 emissionrelative to HCO+ J=4-3 could be used to detect more energetic activity thannormal starbursts, including deeply buried AGNs, in dusty galaxy populations.

ALMA Observations of Nearby Luminous Infrared Galaxies with Various AGN Energetic Contributions Using Dense Gas Tracers