A Uniform Type Ia Supernova Distance Ladder with the Zwicky Transient Facility: Absolute Calibration Based on the Tip of the Red Giant Branch (TRGB) Method

Kavli Affiliate: Wendy L. Freedman

| First 5 Authors: Suhail Dhawan, Ariel Goobar, Joel Johansson, In Sung Jang, Mickael Rigault

| Summary:

The current Cepheid-calibrated distance ladder measurement of $H_0$ is
reported to be in tension with the values inferred from the cosmic microwave
background (CMB), assuming standard cosmology. However, some tip of the red
giant branch (TRGB) estimates report $H_0$ in better agreement with the CMB.
Hence, it is critical to reduce systematic uncertainties in local measurements
to understand the Hubble tension. In this paper, we propose a uniform distance
ladder between the second and third rungs, combining SNe~Ia observed by the
Zwicky Transient Facility (ZTF) with a TRGB calibration of their absolute
luminosity. A large, volume-limited sample of both calibrator and Hubble flow
SNe~Ia from the emph{same} survey minimizes two of the largest sources of
systematics: host-galaxy bias and non-uniform photometric calibration. We
present results from a pilot study using existing TRGB distance to the host
galaxy of ZTF SN~Ia SN 2021rhu (aka ZTF21abiuvdk) in NGC7814. Combining the ZTF
calibrator with a volume-limited sample from the first data release of ZTF
Hubble flow SNe~Ia, we infer $H_0 = 76.94 pm 6.4, {rm km},{rm
s^{-1}},{rm Mpc^{-1}}$, an $8.3 %$ measurement. The error budget is
dominated by the single object calibrating the SN~Ia luminosity in this pilot
study. However, the ZTF sample includes already five other SNe~Ia within $sim$
20 Mpc for which TRGB distances can be obtained with HST. Finally, we present
the prospects of building this distance ladder out to 80 Mpc with JWST
observations of more than one hundred ZTF SNe~Ia.

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