Tip of the Red Giant Branch
These are just some references and unstructured notes at this point.
Tip of the Red Giant Branch as a Distance Indicator
Video of a presentation by Mark Reid at the KITP-UCSB conference Tensions between the Early and the Late Universe on July 16, 2019: H0: NGC 4258 and the Megamaser Cosmology Project | KITP_h0tTakes tweets |
TGRB method – another method useful in measuring the Hubble constant H0, in addition to the cosmic distance ladder, inverse distance ladder, megamasers, H0liCOW time-delay gravitational lensing, gravitational waves, CMB, etc.
Wikipedia: Tip of the Red Giant Branch
The Carnegie Supernova Project: Absolute Calibration and the Hubble Constant https://arxiv.org/abs/1809.06381
The Carnegie-Chicago Hubble Program. I. An Independent Approach to the Extragalactic Distance Scale Using only Population II Distance Indicators https://arxiv.org/abs/1604.01788
A promising alternative to Cepheids is the Tip of the Red Giant Branch (TRGB) method (Madore et al. 2009; Jang et al. 2017). A significant advantage with TRGB is that the older stellar populations being considered are found in both early- and late-type galaxies, allowing for potentially more nearby calibrating SN Ia hosts. The method is also typically carried out in the outskirts of the hosts, reducing the crowding significantly. The Carnegie-Chicago Hubble Program (CCHP; Beaton et al 2016; Freedman 2018) aims to measure H0 using population II distance indicators and the CSP-I and CSP-II samples will be a significant component of their work. For the purposes of this paper, we will forgo using the existing TRGB sample as it is rather sparse and lacks SNe Ia that were observed in the NIR. We therefore use the Cepheid sample of Riess et al. (2016) to calibrate our Hubble diagram as it is the most comprehensive dataset under a single photometric system. In the following sections, we present the general method, then consider different data subsamples and their effects on the derived value of H0. excerpt from The Carnegie Supernova Project: Absolute Calibration and the Hubble Constant [1809.06381]
https://arxiv.org/abs/1703.10616 The Carnegie-Chicago Hubble Program. III. The Distance to NGC 1365 via the Tip of the Red Giant Branch The aim of the Carnegie-Chicago Hubble Program (CCHP) is a direct route to H0 using Type Ia supernovae (SNe Ia) calibrated entirely via Population (Pop) II stars. The SNe Ia zero point is determined using a distance ladder built from RR Lyrae (RRL) and the Tip of the Red Giant Branch (TRGB) distances to Local Group galaxies. This zero point is then applied to the full sample of SNe Ia in the smooth Hubble flow to arrive at a local, direct estimate of H0. Eventually, the TRGB will be calibrated in the Galaxy based on Gaia trigonometric parallaxes for a three step route to the Hubble constant.Since this path is independent of the traditional Pop I Cepheid distance scale that currently sets the SNe Ia zero point, it has the potential to provide insight into the growing (now>3-σ) difference inthe value of H0 as determined by direct (the distance ladder; e.g.Freedman et al. 2012; Riess et al.2016) and indirect methods (via modeling of the Cosmic Microwave Background; e.g.Komatsu et al. 2011;Planck Collaboration et al. 2016)
Tip of the Red Giant Branch as a Distance Indicator The tip of the red giant branch (TRGB) method is a powerful, Pop II distance indicator. It uses the I-band luminosity of the brightest RGB stars. It turns out that in this wavelength, the magnitude of the TRGB stars is very insensitive to metallicity, and also to age.
RR Lyrae variable class of stars https://en.wikipedia.org/wiki/RR_Lyrae_variable
inverse distance ladder method; First Cosmological Results using Type Ia Supernovae from the Dark Energy Survey: Measurement of the Hubble Constant https://arxiv.org/abs/1811.02376 Our measurement makes minimal assumptions about the underlying cosmological model, and our analysis was blinded to reduce confirmation bias. We examine possible systematic uncertainties and all are presently below the statistical uncertainties. Our H0 value is consistent with estimates derived from the Cosmic Microwave Background assuming a LCDM universe (Planck Collaboration et al. 2018). traditional measurements of H0 with SNe Ia use a distance ladder of parallax and Cepheid variable stars, the inverse distance ladder relies on absolute distance measurements from the BAOs to calibrate the intrinsic magnitude of the SNe Ia. a new paper (https://arxiv.org/abs/1811.00537 ) @LloydEKnox, K. Aylor, M. Joy, @cosmic_mar, S. Raghunathan, and K. Wu, called “Sounds Discordant: Classical Distance Ladder and LCDM-based Determinations of the Cosmological Sound Horizon.” ___ Excerpts from Have We Mis-Measured the Universe: SciAm article by Corey S. Powell
everything we know about the origin of the sound horizon depends on a theoretical model of how the universe behaved during its unseen initial 380,000 years. If the models are wrong and the size of the sound horizon is different than what they predict, that adjustment would change all of the numbers derived from it, including the Hubble constant.
Researchers already invoke dark matter to explain galactic motion and dark energy to account for the universe’s accelerating expansion. The divergent measurements of the Hubble constant may be the first sign of the existence of a third dark component, Knox argues—a “dark turbo,†perhaps, that added to the energy of the early universe, hastening its expansion and changing the pitch of its sounds. A related possibility is dark energy has more than one form, or changes over time in complicated ways. A recent study of 1,598 distant quasars using NASA’s Chandra X-Ray Observatory offers intriguing, if preliminary, evidence for the latter interpretation.
New observations of the early universe by the South Pole Telescope in Antarctica and the Atacama Cosmology Telescope in Chile will further probe the sound horizon. Knox is also part of a proposed next-generation ground-based project called CMB-S4 that intends to map the polarization of the microwave sky with great sensitivity. Further, Freedman is nearly finished with her comprehensive data re-analysis. Studies of gravitational waves will provide a completely independent way to assess the true Hubble value as well.
she is developing a new type of distance measurement using red giant stars as reference points. At the same time, she is running a double-blind experiment to reanalyze all of her existing data for bias and mistakes. ___