Merger-induced star formation in the low-metallicity dwarf galaxy NGC 4809/4810

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 CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei 230026, PR China
⁴ School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, PR China
⁵ Frontiers Science Center for Planetary Exploration and Emerging Technologies, University of Science and Technology of China, Hefei, Anhui 230026, PR China

Received: 27 April 2023
Accepted: 2 August 2023

Abstract

Context. The physical mechanisms driving starbursts in dwarf galaxies are unclear, and the effects of mergers on star formation in these galaxies are still uncertain.

Aims. We explore how the merger process affects star formation in metal-poor dwarf galaxies by analyzing high spatial resolution (∼70 pc) integral field spectrograph observations of ionized gas.

Methods. We used archival data from the Very Large Telescope/Multi Unit Spectroscopic Explorer to map the spatial distribution of strong emission lines (e.g., Hβ, Hα, [O III] λ5007, and [N II] λ6583) in the nearby merging star-forming dwarf galaxy system NGC 4809/4810.

Results. We identify 112 star-forming knots scattered among the two galaxies, where the gas-phase metallicity distribution is inhomogeneous and mixes with metal-poor and metal-rich ionized gas. Star-forming knots at the interacting region show lower metallicity, the highest star formation rates (SFRs), and the highest ratio of the SFR to the resolved main-sequence relation (rMSR). Ionized gas exhibits an obvious northeast–southwest velocity gradient in NGC 4809, but appears to be mixed in NGC 4810. The high virial parameters and the stellar mass-size relation of the H II regions indicate that these regions are dominated by direct radiation pressure from massive stars (or clusters) and expand persistently. We find two different relations of the stellar mass surface density to stellar age in NGC 4809 and NGC 4810, and the stellar ages of NGC 4810 are systematically younger than those in NGC 4809.

Conclusions. Our study suggests that the merging stage of two dwarf galaxies can induce starburst activities in the interaction areas despite the metal-deficient environment. Considering the high specific SFRs and different stellar ages, we propose that the interaction initially triggered star formation in NGC 4809 and then drove star formation in NGC 4810.