Star formation traced by optical and millimeter hydrogen recombination lines and free-free emissions in the dusty merging galaxy NGC 3256 -- MUSE/VLT and ALMA synergy

Abstract

A galaxy-galaxy merger and the subsequent triggering of starburst activity are fundamental processes linked to the morphological transformation of galaxies and the evolution of star formation across the history of the Universe. Both nuclear and disk-wide starbursts are assumed to occur during the merger process. However, quantifying both nuclear and disk-wide star formation activity is non-trivial because the nuclear starburst is dusty in the most active merging starburst galaxies. This paper presents a new approach to this problem: combining hydrogen recombination lines in optical, millimeter, and free-free emission. Using NGC~3256 as a case study, H$\beta$, H40$\alpha$, and free-free emissions are investigated using the Multi Unit Spectroscopic Explorer at the Very Large Telescope of the European Southern Observatory (MUSE/VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA). The H$\beta$ image obtained by MUSE identifies star-forming regions outside the nuclear regions, suggesting a disk-wide starburst. In contrast, the H40$\alpha$ image obtained by ALMA identifies a nuclear starburst where optical lines are undetected due to dust extinction ($A_{\mathrm{V}}\sim 25$). Combining both MUSE and ALMA observations, we conclude that the total SFR is $49\pm 2M_{\odot }$~yr${}^{-1}$ and the contributions from nuclear and disk-wide starbursts are $\sim 34\%$ and $\sim 66\%$, respectively. This suggests the dominance of disk-wide star formation in NGC~3256. In addition, pixel-by-pixel analyses for disk-wide star-forming regions suggest that shock gas tracers (e.g., CH${}_3$OH) are enhanced where gas depletion time (${\tau }_{\mathrm{gas}}$=$M_{\mathrm{gas}}/SFR$) is long. This possibly means that merger-induced shocks regulate disk-wide star formation activities.

APJ accepted

References in corpus (15)

• The MUSE second-generation VLT instrument
• Metallicity Effects on Dust Properties in Starbursting Galaxies
• The Oxygen Abundances of Luminous and Ultraluminous Infrared Galaxies
• ALMA Imaging of HCN, CS and dust in Arp 220 and NGC 6240
• The MUSE Atlas of Disks (MAD): Resolving Star Formation Rates and Gas Metallicities on < 100pc Scales
• On carbon and oxygen isotope ratios in starburst galaxies: New data from NGC253 and Mrk231 and their implications
• A Luminous Infrared Merger with Two Bipolar Molecular Outflows: ALMA and SMA Observations of NGC 3256
• ALMA observations of 99 GHz free-free and H40$\alpha$ line emission from star formation in the centre of NGC 253
• VLT-SINFONI integral field spectroscopy of low-z luminous and ultraluminous infrared galaxies I. Atlas of the 2D gas structure
• Free-free and H42alpha emission from the dusty starburst within NGC 4945 as observed by ALMA
• The spatially resolved star formation history of mergers: A comparative study of the LIRGs IC1623, NGC6090, NGC2623, and Mice
• Infrared and X-Ray Evidence of an AGN in the NGC 3256 Southern Nucleus
• An infrared study of the double nucleus in NGC3256
• Tests of star formation metrics in the low metallicity galaxy NGC 5253 using ALMA observations of H30$\alpha$ line emission
• The unusual distribution of molecular gas and star formation in Arp 140

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