Comparative Analysis of TRGBs (CATs) from Unsupervised, Multi-halo-field Measurements: Contrast is Key

The tip of the red giant branch (TRGB) is an apparent discontinuity of the luminosity function (LF) due to the end of the red giant evolutionary phase and is used to measure distances in the local universe. In practice, tip localization via edge detection response (EDR) relies on several methods app...

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Bibliographic Details
Published in:The Astrophysical journal 2023-09, Vol.954 (1), p.87
Main Authors: Wu, J., Scolnic, D., Riess, A. G., Anand, G. S., Beaton, R., Casertano, S., Ke, X., Li, S.
Format: Article
Language:English
Subjects:
Astronomy & Astrophysics
ASTRONOMY AND ASTROPHYSICS
Astrophysics
Dispersion
Distance indicators
Edge detection
Galaxies
Luminosity
Metallicity
Red giant stars
Spatial filtering
Spatial smoothing
Standard candles
Standardization
Stellar distance
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Summary:The tip of the red giant branch (TRGB) is an apparent discontinuity of the luminosity function (LF) due to the end of the red giant evolutionary phase and is used to measure distances in the local universe. In practice, tip localization via edge detection response (EDR) relies on several methods applied on a case-by-case basis. It is hard to evaluate how individual choices affect a distance estimation using only a single host field while also avoiding confirmation bias. To devise a standardized approach, we compare unsupervised , algorithmic analyses of the TRGB in multiple halo fields per galaxy. We first optimize methods for the lowest field-to-field dispersion, including spatial filtering, smoothing, and weighting of LF, color band selection, and tip selection based on the number of likely RGB stars and the ratio of stars below versus above the tip ( R ). We find R , which we call the tip contrast , to be the most important indicator of the quality of EDR measurements; higher R selection can decrease field-to-field dispersion. Further, since R is found to correlate with the age or metallicity of the stellar population based on theoretical modeling, it might result in a displacement of the detected tip magnitude. We find a tip-contrast relation with a slope of −0.023 ± 0.0046 mag/ratio, an ∼5 σ result that can be used to correct these variations in the detections. When using TRGB to establish a distance ladder, consistent TRGB standardization using tip-contrast relation across rungs is vital to make robust cosmological measurements.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/acdd7b