ALMA Observations of Warm Dense Gas in NGC 1614 --- Breaking of Star Formation Law in the Central kpc

TL;DR

This study uses ALMA observations to analyze warm dense gas in NGC 1614, revealing a molecular ring with intense star formation and a breakdown of the Kennicutt-Schmidt law at 100 pc scales.

Contribution

First high-resolution ALMA imaging of CO (6-5) and dust in NGC 1614's central kpc, showing star-forming knots and the breakdown of star formation law.

Findings

Molecular ring contains seven star-forming knots.

Strong deviation from Kennicutt-Schmidt law at 100 pc scale.

No evidence of a Compton-thick AGN in NGC 1614.

Abstract

We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435um dust continuum emission in the central kpc of NGC 1614, a local luminous infrared galaxy (LIRG) at a distance of 67.8 Mpc (1 arcsec = 329 pc). The CO emission is well resolved by the ALMA beam (0".26 x 0".20) into a circum-nuclear ring, with an integrated flux of f_{CO(6-5)} = 898 (+-153) Jy km/s, which is 63(+-12)% of the total CO(6-5) flux measured by Herschel. The molecular ring, located between 100pc < r < 350pc from the nucleus, looks clumpy and includes seven unresolved (or marginally resolved) knots with median velocity dispersion of 40 km/s. These knots are associated with strong star formation regions with \Sigma_{SFR} 100 M_\sun/yr/kpc^{2} and \Sigma_{Gas} 1.0E4 M_\sun/pc^{2}. The non-detections of the nucleus in both the CO (6-5) line emission and the 435um continuum rule out, with relatively high confidence, a Compton-thick AGN in NGC 1614. Comparisons with radio continuum emission show a strong deviation from an expected local correlation between \Sigma_{Gas} and \Sigma_{SFR}, indicating a breakdown of the Kennicutt-Schmidt law on the linear scale of 100 pc.