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Deep imaging of the very isolated dwarf galaxy NGC6789

Ignacio Trujillo, Sergio Guerra Arencibia, Ignacio Ruiz Cejudo, Mireia Montes, Miguel R. Alarcon, Miquel Serra-Ricart

TL;DR

NGC 6789 is an extremely isolated dwarf galaxy whose recent central star formation makes up about 4% of its total stellar mass, presenting a fueling problem in a Local Void environment. The authors use deep multiband optical imaging with the 2.0-m TTT3 telescope and COLORS to search for faint tidal features or residual merger signatures that could supply the gas. They reach surface-brightness depths of 29.8, 29.4, 28.9 mag per square arcsecond in g, r, i and find no evidence of tidal disturbances; the outer morphology remains elliptical to the deepest levels, and a central color gradient is detected. They place quantitative limits on possible accreted stellar debris (roughly two hundred thousand solar masses) and infer a required gas reservoir of at least about ten million solar masses, suggesting the central starburst arises from either in-situ residual gas or recent accretion of pristine gas not associated with minor mergers. This work clarifies how star formation can proceed in highly isolated dwarfs without visible merger activity, informing models of gas accretion and internal gas retention in low-density environments.

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.

Deep imaging of the very isolated dwarf galaxy NGC6789

TL;DR

NGC 6789 is an extremely isolated dwarf galaxy whose recent central star formation makes up about 4% of its total stellar mass, presenting a fueling problem in a Local Void environment. The authors use deep multiband optical imaging with the 2.0-m TTT3 telescope and COLORS to search for faint tidal features or residual merger signatures that could supply the gas. They reach surface-brightness depths of 29.8, 29.4, 28.9 mag per square arcsecond in g, r, i and find no evidence of tidal disturbances; the outer morphology remains elliptical to the deepest levels, and a central color gradient is detected. They place quantitative limits on possible accreted stellar debris (roughly two hundred thousand solar masses) and infer a required gas reservoir of at least about ten million solar masses, suggesting the central starburst arises from either in-situ residual gas or recent accretion of pristine gas not associated with minor mergers. This work clarifies how star formation can proceed in highly isolated dwarfs without visible merger activity, informing models of gas accretion and internal gas retention in low-density environments.

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 in the Sloan g, r, and i filters, respectively, and reveal no evidence of tidal features or merger remnants down to 30 mag arcsec (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.

Paper Structure

This paper contains 2 sections, 1 figure.

Table of Contents

  1. Introduction
  2. TTT3 very deep imaging

Figures (1)

  • Figure 1: NGC6789 as seen by the Sloan Digital Sky Survey (left panel) and the deep image obtained using the TTT3 telescope (right panel). In both cases, the color images were created using a combination of Sloan g, r, and i filters. At the galaxy's distance of 3.6 Mpc, one arcmin corresponds to approximately 1.1 kpc. The black-and-white background of the image corresponds to the g-band image, which is our deepest dataset.