Sub-kpc star-formation law in the local luminous infrared galaxy IC 4687 as seen by ALMA

M. Pereira-Santaella; L. Colina; S. García-Burillo; P. Planesas; A. Usero; A. Alonso-Herrero; S. Arribas; S. Cazzoli; B. Emonts; J. Piqueras López; M. Villar-Martín

doi:10.1051/0004-6361/201527693

paper

Sub-kpc star-formation law in the local luminous infrared galaxy IC 4687 as seen by ALMA

arXiv:1601.02427 · doi:10.1051/0004-6361/201527693

Abstract

We analyze the spatially resolved (250 pc scales) and integrated star-formation (SF) law in the local luminous infrared galaxy (LIRG) IC4687. This is one of the first studies of the SF law on a starburst LIRG at these small spatial scales. We combined new interferometric ALMA CO(2-1) data with existing HST/NICMOS Pa $α$ narrow-band imaging and VLT/SINFONI near-IR integral field spectroscopy to obtain accurate extinction corrected SF rate (SFR) and cold molecular gas surface densities ( $Σ_{g a s}$ and $Σ_{S F R}$ ). We find that IC4687 forms stars very efficiently with an average depletion time ( $t_{d e p}$ ) of 160 Myr for the individual 250 pc regions. This is approximately one order of magnitude shorter than the $t_{d e p}$ of local normal spirals and also shorter than that of main-sequence high-z objects, even when we use a Galactic $α_{C O}$ conversion factor. This result suggests a bimodal SF law in the $Σ_{S F R} \propto Σ_{g a s}^{N}$ representation. A universal SF law is recovered if we normalize the $Σ_{g a s}$ by the global dynamical time. However, at the spatial scales studied here, we find that the SF efficiency (or $t_{d e p}$ ) does not depend on the local dynamical time for this object. Therefore, an alternative normalization (e.g., free-fall time) should be found if a universal SF law exists at these scales.

Accepted for publication in A&A;10 pages, 9 figures. Fixed typos

Sub-kpc star-formation law in the local luminous infrared galaxy IC 4687 as seen by ALMA

Abstract

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