The molecular gas resolved by ALMA in the low-metallicity merging dwarf galaxy Haro 11

¹ School of Astronomy and Space Science, Nanjing University, Nanjing 210093, PR China
e-mail: yulong@nju.edu.cn
² Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, PR China
³ School of Physics and Technology, Nanjing Normal University, Nanjing 210023, PR China
⁴ Institute of Astronomy, The University of Tokyo, Osawa 2-21-1, Mitaka, Tokyo 181-0015, Japan
⁵ CEA, Irfu, DAp, AIM, Université Paris-Saclay, Université de Paris, CNRS, 91191 Gif-sur-Yvette, France
⁶ Stockholm University, Department of Astronomy and Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, SE 10691, Stockholm, Sweden

Received: 27 September 2021
Accepted: 11 February 2022

Abstract

Context. The physical mechanisms driving starbursts and quenching in less massive (M_* ≤ 10¹⁰ M_⊙) galaxies are unclear. The merger is one of the inescapable processes referred to as both starburst and quenching in massive galaxies. However, the effects of the merger on star formation in dwarf galaxies and their evolution are still uncertain.

Aims. We aim to explore how star formation in dwarf galaxies is both triggered and quenched by studying metal-poor gas-rich dwarf mergers based on multi-band observations at a spatial resolution of ∼460 pc.

Methods. We use archival data of Atacama Large Millimetre Array (Band 3 and 8) and Very Large Telescope/Multi Unit Spectroscopic Explorer to map CO(J = 1–0), [CI](³P₁–³P₀), and Hα emission in one of the most extreme merging starburst dwarf galaxies, Haro 11.

Results. We find the molecular gas is assembled around the central two star-forming regions (knots B and C). The molecular and ionized gas and stellar components show complex kinematics, indicating that the gas is probably at a combined stage of collision of clouds and feedback from star formation. The peak location and distribution of [CI](1–0) closely coincide with the CO(1–0) emission, meaning that it might trace the same molecular gas as CO in such a dwarf merger starburst galaxy. The enhancement of line ratios (∼0.5) of [CI]/CO around knot C is probably generated by the dissociation of CO molecules by cosmic rays and far-ultraviolet photons. Globally, Haro 11 and its star-forming regions share similar star formation efficiency (SFE) to the high-z starburst galaxies or the clumps in nearby ultraluminous infrared galaxies.

Conclusions. Given the high SFE, the high specific star formation rate, small stellar mass, low metallicity, and deficient HI gas, Haro 11 could be an analog of a high-z dwarf starburst and the potential progenitor of the nearby less massive elliptical galaxies. The significantly smaller turbulent pressure and viral parameter is probably triggering the intense starbursts. We predict that Haro 11 will quench at M_* ≤ 8.5  ×  10⁹ M_⊙.