Alma observations of warm dense gas in NGC 1614 - Breaking of the star formation law in the central kiloparsec

Abstract

We present ALMA Cycle-0 observations of the CO (65) line emission and of the 435μm dust continuum emission in the central kiloparsec of NGC 1614, a local luminous infrared galaxy at a distance of 67.8 Mpc (1″ = 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 fCO(65) = 898 (±153) Jy km s?1, which is 63(±12)% of the total CO (65) 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 ∑SFR ∼ 100M- yr?1 kpc?2 and ∑Gas ∼ 104 M⊙ pc?2. The nondetections of the nucleus in both the CO (65) line emission and the 435?mcontinuum 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 ∑Gas and ∑SFR, indicating a breakdown of the KennicuttSchmidt law on the linear scale of ∼100 pc.