Spatially resolved radio-to-far-infrared SED of the luminous merger remnant NGC 1614 with ALMA and VLA

Abstract

We present the results of Atacama Large Millimeter/Submillimeter Array (ALMA) 108-, 233-, 352-, and 691-GHz continuum observations and Very Large Array (VLA) 4.81- and 8.36-GHz observations of the nearby luminous merger remnant NGC 1614. By analyzing the beam (1′′.0 × 1′′.0) and uv (≥45 kλ) matched ALMA and VLA maps, we find that the deconvolved source size of lower-frequency emission (≤108 GHz) is more compact (420 pc × 380 pc) compared to the higher-frequency emission (≥233 GHz) (560 pc × 390 pc), suggesting different physical origins for the continuum emission. Based on a spectral energy distribution (SED) model for a dusty starburst galaxy, it is found that the SED can be explained by three components: (1) non-thermal synchrotron emission (traced in the 4.81- and 8.36-GHz continua), (2) thermal free–free emission (traced in the 108-GHz continuum), and (3) thermal dust emission (traced in the 352- and 691-GHz continua). We also present the spatially resolved (sub-kpc scale) Kennicutt–Schmidt relation of NGC 1614. The result suggests a systematically shorter molecular gas depletion time in NGC 1614 (average τ_(gas) of 49–77 Myr and 70–226 Myr at the starburst ring and the outer region, respectively) than that of normal disk galaxies (∼2 Gyr) and a mid-stage merger VV 114 (= 0.1–1 Gyr). This implies that the star formation activities in (ultra-)luminous infrared galaxies are efficiently enhanced as the merger stage proceeds, which is consistent with the results from high-resolution numerical merger simulations.

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