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Ultra-long-period Cepheids (ULPCs) are important in distance-scale studies due to their potential for determining distance beyond ∼ 100 Mpc. We performed a comprehensive search for ULPCs in M31, a local benchmark to calibrate the distance ladders. We use data from the Palomar Transient Factory (PTF), which has imaged M31 using a 1.2-m telescope equipped with a ≈7.26 deg2 field-of-view (FOV) camera,...
Recent simulations, as well as weak lensing and X-ray data, indicate that gas is a good tracer of the total mass in clusters. The constancy of the gas fraction f g in clusters of galaxies can thus be used as a novel distance indicator f g ≃h 32 Ω b /Ω 0 . Assuming spherical symmetry and hydrostatic equilibrium allows us to infer f g using only the...
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