Updated Hubble constant from TRGB measurements

[Madeleine Birchfield]

Scolnic et al have put out a new preprint with an updated value for the Hubble constant as measured from the Tip of the Red Giant Branch:

https://arxiv.org/abs/2304.06693

 

[ohwilleke]

CATS: The Hubble Constant from Standardized TRGB and Type Ia Supernova Measurements​

D. Scolnic, A. G. Riess, J. Wu, S. Li, G. S. Anand, R. Beaton, S. Casertano, R. Anderson, S. Dhawan, X. Ke

The Tip of the Red Giant Branch (TRGB) provides a luminous standard candle for constructing distance ladders to measure the Hubble constant. In practice its measurements via edge-detection response (EDR) are complicated by the apparent fuzziness of the tip and the multi-peak landscape of the EDR. As a result, it can be difficult to replicate due to a case-by-case measurement process.

Previously we optimized an unsupervised algorithm, Comparative Analysis of TRGBs (CATs), to minimize the variance among multiple halo fields per host without reliance on individualized choices, achieving state-of-the-art ∼ < 0.05 mag distance measures for optimal data.

Further, we found an empirical correlation at 5σ confidence in the GHOSTS halo survey between our measurements of the tip and their contrast ratios (ratio of stars 0.5 mag just below and above the tip), useful for standardizing the apparent tips at different host locations.

Here, we apply this algorithm to an expanded sample of SN Ia hosts to standardize these to multiple fields in the geometric anchor, NGC 4258.

In concert with the Pantheon+ SN Ia sample, this analysis produces a (baseline) result of H0=73.22±2.06 km/s/Mpc. The largest difference in H0 between this and similar studies employing the TRGB derives from corrections for SN survey differences and local flows used in most recent SN Ia compilations but which were absent in earlier studies. SN-related differences total ∼ 2.0 km/s/Mpc. A smaller share, ∼ 1.4 km/s/Mpc, results from the inhomogeneity of the TRGB calibration across the distance ladder.

We employ a grid of 108 variants around the optimal TRGB algorithm and find the median of variants is 72.94±1.98 km/s/Mpc with an additional uncertainty due to algorithm choices of 0.83 km/s/Mpc. None of these TRGB variants result in H0 less than 71.6 km/s/Mpc.

Comments:

Submitted to ApJL, comments welcome

 

[Bandersnatch]

That's quite a bit northwards of previous TRGB determinations:

(Freedman et al. 2019; fig.17)

 

[pinball1970]

This is my pop ups yesterday

https://phys.org/news/2023-05-first-of-its-kind-universe-expansion-longstanding-debate.html

Not sure I get why there would be more than one image separated by time.

https://www.science.org/doi/10.1126/science.abh1322

 

[Bandersnatch]

Not sure I get why there would be more than one image separated by time.

The light from the supernova follows different paths around the lensing galaxy cluster. Some paths are longer than others, so it takes correspondingly more or less time. Imagine a light beam going straight to you, and another making a detour - it'd normally leave the source in a direction unaligned with the observer, but the gravity well bends its path so that it turns around towards you. The turning around takes some time, so to speak.