AVID: Formation and evolution of a coalesced major merger of late-type dwarf galaxies (VCC 479) on the outskirts of the Virgo cluster

¹ Department of Astronomy, University of Science and Technology of China, Hefei 230026, China
² School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, China
³ Departamento de Fisica, Universidad Tecnica Federico Santa Maria, Avenida España 1680, Valparaíso, Chile
⁴ Millenium Nucleus for Galaxies (MINGAL), Chile
⁵ Centre for strophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
⁶ National Research Council of Canada, Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
⁷ Department of Astronomy and Space Science, Sejong University, Seoul 05006, Korea
⁸ Department of Physics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong S.A.R., China
⁹ Aix-Marseille Univ., CNRS, CNES, LAM, Marseille, France
¹⁰ University of Calgary, 2500 University Drive NW, Calgary Alberta T2N 1N4, Canada
¹¹ Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg (ObAS), UMR 7550, F-67000 Strasbourg, France
¹² UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
¹³ Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011, People’s Republic of China
¹⁴ State Key Laboratory of Radio Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
¹⁵ Department of Astronomy, Yonsei University, Seoul 03722, Republic of Korea
¹⁶ Center for Galaxy Evolution Research, Yonsei University, Seoul 03722, Republic of Korea
¹⁷ NSF NOIRLab, 950 N. Cherry Avenue, Tucson, AZ 85719, USA
¹⁸ Department of Astronomy, Peking University, Beijing 100871, China
¹⁹ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People’s Republic of China
²⁰ Università di Milano-Bicocca, Piazza della Scienza 3, 20100 Milano, Italy
²¹ AIM, CEA, CNRS, Université Paris-Saclay, Université Paris-Diderot, Sorbonne Paris-Cité Observatoire de Paris, PSL University, 91191 Gif-sur-Yvette Cedex, France

^⋆ Corresponding author: hzhang18@ustc.edu.cn

Received: 9 May 2025
Accepted: 16 June 2025

Abstract

Context. Dwarf-dwarf galaxy mergers are among the least explored aspects of dwarf galaxy pre-processing as they fall into clusters.

Aims. We present the first case study of a coalesced late-type dwarf major merger (VCC 479; stellar mass ∼ 8 × 10⁷ M_⊙) that has undergone significant environmental influence, with the aim of exploring dwarf galaxy evolution under the combined effects of galaxy interactions and environmental processes, and understanding its relevance to the diversity of dwarf galaxies in cluster environments.

Methods. Our analysis is based on multifrequency observations, including VLA and FAST HI emission line mapping from the Atomic gas in Virgo Interacting Dwarf galaxies (AVID) survey, and existing ultraviolet and optical images. We also performed idealized hydrodynamical simulations of dwarf-dwarf mergers to help us interpret the observations.

Results. We identify symmetric stellar shell structures in VCC 479, indicative of a coalesced major merger of dwarf galaxies. The galaxy features a central starburst, initiated ∼600 Myr ago, embedded within an exponential disk quenched ∼1 Gyr ago. The starburst contributes only 2.9 ± 0.5% of the total stellar mass, and VCC 479’s global star formation rate is 0.3 dex lower than typical dwarfs of a similar mass. The galaxy is highly HI-deficient, with most HI gas concentrated within the central 1 kpc and little extended HI envelope. The misalignment of the HI velocity field with the stellar body is best explained by merger-triggered gas inflow, as is seen in our simulations.

Conclusions. Our analysis is consistent with a scenario in which the majority of HI gas of the progenitor galaxies was removed by the cluster environment prior to the final coalescence. The merger concentrates the remaining gas toward the galaxy center, triggering a central starburst. The combined effect of environment stripping and galaxy merger has transformed VCC 479 into a blue-core dwarf undergoing a morphological transition from a late-type to an early-type galaxy.