The dwarf galaxy satellite system of Centaurus A (1907.02012v2)

Abstract: Dwarf galaxy satellite systems are essential probes to test models of structure formation, making it necessary to establish a census of dwarf galaxies outside of our own Local Group. We present deep FORS2 VI band images from the ESO Very Large Telescope for 15 dwarf galaxy candidates in the Centaurus group of galaxies. We confirm nine dwarfs to be members of CenA by measuring their distances using a Bayesian approach to determine the tip of the red giant branch luminosity. We have also fitted theoretical isochrones to measure their mean metallicities. The properties of the new dwarfs are similar to those in the Local Group in terms of their sizes, luminosities, and mean metallicities. Within our photometric precision there is no evidence of a metallicity spread, but we do observe possible extended star formation in several galaxies, as evidenced by a population of asymptotic giant branch stars brighter than the red giant branch tip. The new dwarfs do not show any signs of tidal disruption. Together with the recently reported dwarf galaxies by the complementary PISCeS survey, we study the luminosity function and 3D structure of the group. By comparing the observed luminosity function to the high-resolution cosmological simulation IllustrisTNG, we find agreement within a 90% confidence interval. However, CenA seems to be missing its brightest satellites and has an overabundance of the faintest dwarfs in comparison to its simulated analogs. In terms of the overall 3D distribution of the observed satellites, we find that the whole structure is flattened along the line-of-sight, with an root-mean-square (rms) height of 130 kpc and a rms semi major axis length of 330 kpc. Future distance measurements of the remaining dwarf galaxy candidates are needed to complete the census of dwarf galaxies in the Centaurus group.

Overview of the Dwarf Galaxy Satellite System of Centaurus A

The paper presented investigates the satellite dwarf galaxy system surrounding Centaurus A (Cen A), marked as a significant effort in understanding galaxy formation and evolution beyond our Local Group. Utilizing deep FORS2 $VI$ band images from the ESO Very Large Telescope (VLT), the researchers aimed to confirm membership of dwarf galaxy candidates to the Centaurus A system through precise distance measurements and analysis of their structural properties.

Methodology and Findings

The methodology employed includes a Bayesian approach to determine the tip of the red giant branch (TRGB) luminosity, enabling accurate distance estimations for 15 dwarf galaxy candidates. The research successfully confirms nine candidates as members of Cen A, measuring distances with an accuracy of about 5%. This precision is crucial for constructing the 3D spatial distribution of galaxies in the Centaurus group and analyzing their luminosity function.

The properties of these new dwarfs have been determined, showing similarities to those in the Local Group concerning sizes, luminosities, and mean metallicities. Notably, there is no significant evidence of metallicity spread within individual galaxies, which suggests similar formation histories or limitations due to photometric precision. Furthermore, the paper did not observe any signs of tidal disruption among the new dwarfs, indicating stability within the satellite system.

A fascinating aspect of the research is the analysis of the observed luminosity function in comparison to high-resolution cosmological simulations (IllustrisTNG). The results demonstrate agreement within a 90% confidence interval, although with discrepancies: Cen A appears to lack some of the brightest satellites and exhibits an overabundance of faint dwarfs compared to simulations.

Implications and Future Directions

The implications of the findings are both theoretical and practical. They contribute to a larger understanding of galaxy group dynamics and satellite distribution, important for refining cosmological models, particularly in addressing the missing satellite problem prevalent in discussions of dark matter and galaxy evolution.

The dwarf galaxy system around Cen A provides a crucial testing ground for theories predicting galaxy distribution patterns. Given the observed flatness along the line-of-sight, future studies might consider examining potential causes beyond measurement uncertainties, such as intrinsic flattening or survey limitations due to galactic obstruction.

Continued exploration in this field promises to shed light on small-scale cosmological issues. To enhance the robustness of the census and validate the profile completeness, future surveys will need to focus on regions with current observational limitations, such as those impacted by Galactic cirrus.

Conclusion

Overall, this paper plays a critical role in the investigation of extragalactic systems, providing new data on dwarf galaxy populations in the Centaurus group, and contributing valuable insights that intersect observational astronomy with theoretical modeling. As the understanding of dwarf galaxies evolves, so too will the potential for developing more refined cosmological models based on observed galaxy structures.