Oral Presentation
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 –
Presenter: Tomonari Michiyama (Kavli Institute for Astronomy and Astrophysics (KIAA))
We present a new approach to investigate spatially resolved star formation activity in nearby active dusty galaxies such as luminous infrared galaxies (LIRGs): combining hydrogen recombination lines in both optical and millimeter and free-free emission. Using NGC 3256 as a case study for a dusty LIRGs, Hβ and H40αemissions are investigated by using MUSE/VLT and ALMA. The Hβ image obtained by MUSE identifies star-forming regions outside of the nuclear regions, suggesting a disk-wide starburst. On the other hand, the H40α image obtained by ALMA identifies a nuclear starburst where optical lines are undetected due to dust extinction (AV ~25). Combining both MUSE and ALMA observation, we conclude that the total SFR is 48.5 Ms/yr and contribution from nuclear and disk-wide starbursts is 34% and 66%, respectively. This suggests the dominance of disk-wide star formation in NGC 3256. In addition, the starburst timescale of ~100 Myr is predicted from comparing the total SFR and infrared luminosity. The shorter starburst timescale, compared to the merger timescale (~500 Myr), suggests that the current starbursts are triggered by a merger process in NGC 3256. Finally, pixel-by-pixel analysis for disk-wide star forming regions suggests that shock gas tracers (e.g., CH3OH) are enhanced where gas depletion time (tau_gas = Mgas/SFR) is long. This possibly means that merger induced shocks regulate disk-wide star formation activities.
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