Astronomers determine distances to 18 dwarf galaxies

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Russian astronomers determine distances to eighteen dwarf galaxies
HST ACS/WFC images of nine galaxies described in the study. Credit: Tikhonov et al., 2020.

Astronomers from the Special Astrophysical Observatory (SAO) in Nizhnij Arkhyz, Russia, have conducted photometric observations of dwarf galaxies identified by the ALFALFA survey. The results allowed the researchers to determine accurate distances of 18 dwarf galaxies. The study is detailed in a paper published October 1 on the arXiv pre-print repository.


Dwarf galaxies, especially these containing hydrogen and located far from neighboring galaxies, are interesting targets for observation. Given that the evolution in such dwarfs occurs without any external influence, they could be crucial in improving our understanding of star formation processes in galaxies.

Researchers find new dwarfs using radio observations in the vicinity of galaxy groups. However, in order to get more insights into their nature, accurate distance measurements are also required. One of the methods to obtain these distances is known as TRGB and is based on measuring the position of the tip of the red giant branch stars.

SAO’s astronomers Olga Galazutdinova and Nikolay A. Tikhonov have used the TRGB technique to accurately determine distances of 18 dwarf galaxies. The dwarfs were detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey, and their images were obtained by the Hubble Space Telescope (HST).

“Based on HST images for 18 dwarf galaxies, we constructed the CM [color magnitude] diagrams on which both young stars (blue and red supergiants) and an old stellar population (red giants) are seen. For each galaxy, we determined the position of the tip of the red giant branch (TRGB jump) and the color index of the RGB. This allowed us to determine the distances to the galaxies and the metallicity of red giants in these galaxies based on the equations from Lee et al. (1993),” the astronomers explained.

According to