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The Dragonfly Galaxy II. ALMA unveils a triple merger and gas exchange in a hyper-luminous radio galaxy at z=2

B. H. C. Emonts ; C. De Breuck ; M. D. Lehnert ; J. Vernet ; B. Gullberg ; M. Villar-Martin ; N. Nesvadba ; Guillame Drouart (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; R. Ivison ; N. Seymour ; D. Wylezalek ; P. Barthel
Astronomy & Astrophysics (1432-0746). Vol. 584 (2015),
[Artikel, refereegranskad vetenskaplig]

The Dragonfly Galaxy (MRC 0152-209), at redshift z similar to 2, is one of the most vigorously star-forming radio galaxies in the Universe. What triggered its activity? We present ALMA Cycle 2 observations of cold molecular CO(6 5) gas and dust, which reveal that this is likely a gas-rich triple merger. It consists of a close double nucleus (separation similar to 4 kpc) and a weak CO-emitter at similar to 10 kpc distance, all of which have counterparts in HST/NICMOS imagery. The hyper-luminous starburst and powerful radio-AGN were triggered at this precoalescent stage of the merger. The CO(6-5) traces dense molecular gas in the central region, and complements existing CO(1-0) data, which reveal more widespread tidal debris of cold gas. We also find similar to 10(10) M-circle dot of molecular gas with enhanced excitation at the highest velocities. At least 20-50% of this high-excitation, high-velocity gas shows kinematics that suggests it is being displaced and redistributed within the merger, although with line-of-sight velocities of vertical bar v vertical bar < 500 km s(-1), this gas will probably not escape the system. The processes that drive the redistribution of cold gas are likely related to either the gravitational interaction between two kpc-scale discs, or starburst/AGN-driven outflows. We estimate that the rate at which the molecular gas is redistributed is at least. M similar to 1200 +/- 500 M-circle dot yr(-1), and could perhaps even approach the star formation rate of similar to 3000 +/- 800 M-circle dot yr(-1). The fact that the gas depletion and gas redistribution timescales are similar implies that dynamical processes can be important in the evolution of massive high-z galaxies.

Nyckelord: galaxies: high-redshift, galaxies: active, galaxies: interactions, infrared: galaxies, submillimeter

Denna post skapades 2016-01-21. Senast ändrad 2016-01-25.
CPL Pubid: 231045


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