Color-magnitude diagram for the 180,000+ sources identified in Fornax. The positions of stars on this plot reveals a great deal about their properties, age, and evolution.
Color-magnitude diagram near the tip of the red giant branch, with the luminosity function and edge-detection kernel on the right. We find a dramatic drop-off in the population at around 16.8 mag, corresponding to this tip. We can measure a distance by the difference between the observed and true brightness of this feature, using a calibration that's well-constrained from stellar physics.
Light curves (brightness over time) for two RR Lyrae variable stars in our sample. We used the known relationship between the period and the mean luminosity of these stars to measure a distance. By observing RR Lyrae in the outer regions of galaxies, we avoided crowding and reddening effects that can complicate this measurement.
Fornax dSph program
- Number of pointings: 9 IMACS + 4 HST
- Photometric catalog: 180,471 sources
- RR Lyrae light curves: 332
- Distance to Fornax: 143 ± 3 kpc
How fast is the Universe expanding?
A great debate over the expansion rate of our Universe is currently shaking cosmology. To measure this number more accurately, reliable distance measurements to neaby galaxies are essential. Using three independent approaches based on Population II stars, which avoid some of the systematic errors that make other methods challenging, we measured distances to the Fornax and Sculptor dwarf spheroidal (dSph) galaxies in Oakes et al. (2022) and Tran et al. (2022). This work helped set a "rung" of the cosmic distance ladder constructed by Freedman (2021).