2024A&A...687A..33O

Context. Compact groups of galaxies are unique places where galaxy-galaxy interactions play a mayor role on the evolution of its members. These strong gravitational encounters can induce star formation bursts.
Aims. We study the properties of one of the most luminous so-called hinge clumps that is located in the compact group of galaxies NGC 6845.
Methods. Using integral field spectroscopy from GMOS/Gemini complemented with archival MUSE data, we obtained oxygen abundances, ages, star formation rates, and velocity fields, and we also modeled a single stellar population to understand the star formation history of the hinge clump in NGC 6845.
Results. We found that the hinge clump sits in a tailthat has a star formation rate of 3.4 M_⊙ yr^–1, which is comparable with a few other extreme cases, for instance, the star clusters in the Antennae galaxy and other reported hinge clumps in the literature. This clump represents ∼15% of total star formation rate of NGC 6845A. Large-scale modeling of the observed velocity field of NGC 6845A rules out the scenario according to which this hinge clump was a satellite galaxy. Its kinematics is compatible with that of the galactic disk of NGC 6845A. Its abundance with a mean value of 0.4 Z_⊙ is also consistent with the metallicity gradient of the galaxy.
Conclusions. Our analysis suggest that the hinge clump is formed by multiple stellar populations and not by a single burst. This causes the wide age range. We found that the central clump is encompassed by a ring-like structure, which might suggest a second generation of star formation. In addition, the analysis of the diagnostic diagram indicates that this central region might also be ionized by shocks from stellar and supernova winds. Finally, the derived star formation rate density Σ = 9.7 M_⊙ yr^–1 kpc^–2 of the central clump places it in starburst regime, where gas inflows should provide gas to maintain the star formation. This work shows a resolved example of an extreme localized starburst in a compact group of galaxies.