GAMA 526784: the progenitor of a globular cluster-rich ultra-diffuse galaxy? II. Molecular gas, neutral gas and environment

TL;DR

This study examines the gas content, star formation, and environment of the ultra-diffuse galaxy GAMA526784, suggesting recent interactions and complex gas dynamics influence its evolution and star formation efficiency.

Contribution

It provides new insights into the gas reservoirs and interaction history of GAMA526784, highlighting the potential role of a nearby companion in its recent star formation activity.

Findings

GAMA526784 has a regular HI reservoir but limited molecular gas detection.

Possible CO-dark H2 or recent interaction may explain the low molecular gas.

A nearby dwarf galaxy may have triggered star formation through a high-velocity encounter.

Abstract

Aims. We investigate the gas reservoirs, star formation (SF) properties, and environment of the ultra-diffuse galaxy GAMA526784 to understand its formation history, the efficiency of molecular gas conversion into stars, and the possible role of an interacting companion in shaping its morphology. Methods. We analyse low and high-resolution CO observations to constrain the molecular gas content, compare with HI data, and examine the SF efficiency of GAMA526784. The potential influence of a newly identified nearby dwarf galaxy is assessed using photometric and spatial information. Results. GAMA526784 exhibits a regular HI reservoir (M_HI/M* = 2.88) but only upper limits on its molecular gas mass (M_H2(5sigma)/M* < 0.23). The HI reservoir and CO non-detection can be explained by several mechanisms: (1) predominance of CO-dark H2, invisible to CO observations but contributing to SF; (2) a time delay in HI-to-H2 conversion following a recent interaction; or (3) elevated turbulence inhibiting gas collapse. An identified companion, found at a projected distance of 48 kpc, shows similar colours and lies in the direction of young star clusters in GAMA526784, indicating a possible association. We hypothesise this companion may have triggered the formation of star clusters in GAMA526784 through a high-velocity encounter. Conclusions. Our findings suggest GAMA526784 may have undergone an interaction that influenced its gas reservoirs and SF activity. The presence of a nearby companion agrees with predictions of a high-speed encounter, potentially offering a rare example of such an interaction in progress. We suggest this encounter may have shaped the system's recent evolution. Future observations, particularly targeting molecular gas tracers beyond CO and resolved HI maps, will be crucial in determining the extent of GAMA526784's cold gas reservoir and the nature of its recent star formation.