The Dragonfly Galaxy: II. ALMA unveils a triple merger and gas exchange in a hyper-luminous radio galaxy at z = 2
Artikel i vetenskaplig tidskrift, 2015

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.


submillimeter: galaxies

galaxies: high-redshift

galaxies: active

infrared: galaxies

galaxies: interactions


B. Emonts

Agencia Estatal Consejo Superior de Investigaciones Científicas (CSIC)

C. De Breuck

European Southern Observatory (ESO)

M. Lehnert

Sorbonne Université

Institut d 'Astrophysique de Paris

J. Vernet

European Southern Observatory (ESO)

B. Gullberg

European Southern Observatory (ESO)

M. Villar-Martin

Universidad Autonoma de Madrid (UAM)

Agencia Estatal Consejo Superior de Investigaciones Científicas (CSIC)

N. Nesvadba

Université Paris-Sud

Guillaume Drouart

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

R. J. Ivison

European Southern Observatory (ESO)

University of Edinburgh

N. Seymour

Curtin University

D. Wylezalek

Johns Hopkins University

P. D. Barthel

Rijksuniversiteit Groningen

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 584


Astronomi, astrofysik och kosmologi


Onsala rymdobservatorium



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