In this talk I show:
- how little h arises in the measurement of galaxies,
- how to compare like-properties from different datasets that have assumed different little h cosmologies, and
- how to fairly compare theoretical data with observed data, where little h can manifest in vastly different ways.
This last point is particularly important when observations are used to calibrate galaxy formation models, as calibrating with the wrong (or no) little h can lead to disastrous results when the model is later converted to the correct h cosmology.
I’ll argue that in this modern age little h is an anachronism, being one of least uncertain parameters in astrophysics, and propose that observers and theorists instead treat this uncertainty like any other.
I’ll conclude with a “cheat sheet” of nine points that should be followed when dealing with little h in data analysis.