2017ApJ...834....6S

We report the detection of two CH₃OH lines (J_K = 2_K-1_K and 3_K-2_K) between the progenitor's disks ("Overlap") of the mid-stage merging galaxy VV 114 obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 and Band 4. The detected CH₃OH emission shows an extended filamentary structure (∼3 kpc) across the progenitor's disks with relatively large velocity width (FWZI ∼ 150 km s^–1). The emission is only significant in the "overlap" and not detected in the two merging nuclei. Assuming optically thin emission and local thermodynamic equilibrium, we found the CH₃OH column density relative to H₂ (X_CH3OH_) peaks at the "Overlap" (∼8 x 10^–9), which is almost an order of magnitude larger than that at the eastern nucleus. We suggest that kpc-scale shocks driven by galaxy-galaxy collision may play an important role to enhance the CH₃OH abundance at the "Overlap." This scenario is consistent with shock-induced large velocity dispersion components of ionized gas that have been detected in optical wavelength at the same region. Conversely, low X_CH3OH_ at the nuclear regions might be attributed to the strong photodissociation by nuclear starbursts and/or a putative active galactic nucleus, or inefficient production of CH₃OH on dust grains due to initial high-temperature conditions (i.e., desorption of the precursor molecule, CO, into gas phase before forming CH₃OH on dust grains). These ALMA observations demonstrate that CH₃OH is a unique tool to address kpc-scale shock-induced gas dynamics and star formation in merging galaxies.