How biased is the extragalactic distance ladder by stellar association?

Richard Anderson & Remco van der Burg

(email advisors)

Let's use deep Hubble Space Telescope observations of pulsating Cepheid stars in the Andromeda galaxy to help solve a cosmic conundrum!

How do we measure distances of galaxies far, far away? And how does this help us measure the expansion of the cosmos? The answer: we carefully calibrate a Cosmic Distance Scale that combines different types of objects (stars and supernovae) and observational techniques (astrometry and photometry). We then use this distance scale to determine the Hubble-Lemaître law that relates recession velocity to distance via the constant H0. However, there is tension in the cosmic web: the most accurate measurements of H0 differ from the value of H0 inferred using high-precision measurements of the Cosmic Microwave Background by the ESA satellite Planck. Is this indicative of new physics beyond LambdaCDM? Or just a measurement error?

With this project, you can contribute to answering these questions by investigating a potential systematic error of the H0 measurement. You will use observations made with the Hubble Space Telescope to quantify the degree by which the physical association of stars (in groups or clusters) biases the calibration of the Cosmic Distance Scale. We anticipate that the results of this project would be an important part of a future publication.

In practice, you will learn about astrophysics (variable stars, distance scale) and cosmology (Hubble-Lemaître law, Hubble tension), develop skills in programming using python, data analysis (image processing), and accessing astronomical data from state-of-the-art archives.

We look forward to working with you in the summer!

#photometry  #cosmology  #stars  #python  #Hubbletension

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