ALMA Observations of Warm Dense Gas in NGC 1614—Breaking of the Star Formation Law in the Central Kiloparsec

We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435 μm dust continuum emission in the central kiloparsec of NGC 1614, a local luminous infrared galaxy at a distance of 67.8 Mpc (1{^{\prime \prime} }= 329 pc). The CO emission is well resolved by the ALMA beam (0.''26 × 0.''20) into a circumnuclear ring, with an integrated flux of f _CO(6-5) = 898 (± 153) Jy km s^-1, which is 63(± 12)% of the total CO (6-5) flux measured by Herschel. The molecular ring, located between 100 pc < r < 350 pc from the nucleus, looks clumpy and includes seven unresolved (or marginally resolved) knots with median velocity dispersion of ~40 km s^-1. These knots are associated with strong star formation regions with Σ_SFR ~ 100 M _⊙ yr^-1 kpc^-2 and Σ _Gas∼ 10⁴ {M}_⊙ pc^-2. The non-detections of the nucleus in both the CO (6-5) line emission and the 435 μm continuum rule out, with relatively high confidence, a Compton-thick active galactic nucleus in NGC 1614. Comparisons with radio continuum emission show a strong deviation from an expected local correlation between Σ_Gas and Σ_SFR, indicating a breakdown of the Kennicutt-Schmidt law on the linear scale of ~100 pc.

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