Deep imaging of the very isolated dwarf galaxy NGC6789

TL;DR

This study presents deep optical imaging of the isolated dwarf galaxy NGC 6789, revealing recent central star formation without signs of tidal disturbances, suggesting internal or external gas accretion as the star formation trigger.

Contribution

First deep imaging of NGC 6789 in the Local Void, providing insights into its recent star formation and gas origin without evidence of mergers.

Findings

Recent star formation accounts for ~4% of stellar mass.

No tidal features or merger remnants detected.

Outer morphology remains undisturbed.

Abstract

We present deep optical imaging of the extremely isolated dwarf galaxy NGC 6789, obtained with the new 2-meter Two-meter Twin Telescope (TTT3) at Teide Observatory. Despite its location in the Local Void, NGC 6789 exhibits surprising recent central star formation equivalent to approximately 4% of its total stellar mass. The origin of the gas necessary for this level of star formation remains unknown. Our data reach surface brightness limits of 29.8, 29.4, and 28.9 mag arcsec$^{-2}$ in the Sloan g, r, and i filters, respectively, and reveal no evidence of tidal features or merger remnants down to $\sim$30 mag arcsec$^{-2}$ (or equivalently, at a radial distance larger than 1.6 kpc). The galaxy's undisturbed outer elliptical morphology suggests that its recent central star formation was likely produced by either in-situ residual gas or by the accretion of external pristine gas not associated with a minor merging activity.