Spatially resolved cold molecular outflows in ULIRGs
Journal article, 2018

We present new CO(2-1) observations of three low-z (d similar to 350 Mpc) ultra-luminous infrared galaxy (ULIRG) systems (six nuclei) observed with the Atacama large millimeter/submillimeter array (ALMA) at high spatial resolution (similar to 500 pc). We detect massive cold molecular gas outflows in five out of six nuclei (M-out - (0.3-5) x 10(8) M-circle dot). These outflows are spatially resolved with deprojected effective radii between 250 pc and 1 kpc although high-velocity molecular gas is detected up to R-max similar to 0.5-1.8 kpc (1-6 kpc deprojected). The mass outflow rates are 12-400 M circle dot yr(-1) and the inclination corrected average velocity of the outflowing gas is 350-550 km s(-1) (v(max) = 500-900 km s(-1)). The origin of these outflows can be explained by the strong nuclear starbursts although the contribution of an obscured active galactic nucleus cannot be completely ruled out. The position angle (PA) of the outflowing gas along the kinematic minor axis of the nuclear molecular disk suggests that the outflow axis is perpendicular to the disk for three of these outflows. Only in one case is the outflow PA clearly not along the kinematic minor axis, which might indicate a different outflow geometry. The outflow depletion times are 15-80 Myr. These are comparable to, although slightly shorter than, the star-formation (SF) depletion times (30-80 Myr). However, we estimate that only 15-30% of the outflowing molecular gas will escape the gravitational potential of the nucleus. The majority of the outflowing gas will return to the disk after 5-10 Myr and become available to form new stars. Therefore, these outflows will not likely completely quench the nuclear starbursts. These star-forming powered molecular outflows would be consistent with being driven by radiation pressure from young stars (i.e., momentum-driven) only if the coupling between radiation and dust increases with increasing SF rates. This can be achieved if the dust optical depth is higher in objects with higher SF. This is the case in at least one of the studied objects. Alternatively, if the outflows are mainly driven by supernovae (SNe), the coupling efficiency between the interstellar medium and SNe must increase with increasing SF levels. The relatively small sizes (<1 kpc) and dynamical times (<3 Myr) of the cold molecular outflows suggests that molecular gas cannot survive longer in the outflow environment or that it cannot form efficiently beyond these distances or times. In addition, the ionized and hot molecular phases have been detected for several of these outflows, so this suggests that outflowing gas can experience phase changes and indicates that the outflowing gas is intrinsically multiphase, likely sharing similar kinematics, but different mass and, therefore, different energy and momentum contributions.

galaxies: starburst

galaxies: ISM

galaxies: nuclei

galaxies: active

galaxies: kinematics and dynamics

Author

M. Pereira-Santaella

University of Oxford

L. Colina

Consejo Superior de Investigaciones Científicas

S. Garcia-Burillo

Spanish National Observatory (OAN)

F. Combes

Pierre and Marie Curie University (UPMC)

B. Emonts

National Radio Astronomy Observatory

Susanne Aalto

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

A. Alonso-Herrero

Consejo Superior de Investigaciones Científicas

S. Arribas

Consejo Superior de Investigaciones Científicas

C. Henkel

Max Planck Society

King Abdulaziz University

A. Labiano

Consejo Superior de Investigaciones Científicas

Sebastien Muller

Chalmers, Space, Earth and Environment, Onsala Space Observatory, Onsala Space Observatory, Observation Support

J. Piqueras Lopez

Consejo Superior de Investigaciones Científicas

D. Rigopoulou

University of Oxford

P. van der Werf

Leiden University

Astronomy and Astrophysics

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

Vol. 616 A171

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Infrastructure

Onsala Space Observatory

DOI

10.1051/0004-6361/201833089

More information

Latest update

5/20/2019