The TRGB Distance Scale
Resolving Tension in the Hubble Constant

Gaia
HSTPlanck

Wendy Freedman
University of Chicago
Heineman Prize
LectureJanuary 5, 2017

A Crisis in Cosmology?

What should
we believe?

Hubble Constant
10:02:37 am
October 5, 2019

CMBCMB

Walter BaadeOct 23, 1943

NGC 185

14,400 sec “Red Light” ExposureWalter BaadeOct 23, 1943

NGC 185

TRGB in IC 1613
Freedman, W.L. AJ, 96, 1248, 1988

TRGB in IC 1613
Freedman, W.L. AJ, 96, 1248, 1988

TRGB in IC 1613
Freedman, W.L. AJ, 96, 1248, 1988
ICFHT

TRGB in IC 1613Ha[, D., et al., ApJ, 845, 146, 2017
Marginalized
Luminosity
Func_on

HST/ACSSobel
FilterTRGB Sequence
is aStandard Candle

Standard vs Standardizable Candles
Cepheids

TRGB

Type Ia SNe

MechanicalHeat Engine

StandardCandle

StandardBomb

PeriodTemperature
Reddening [Disk]
Metallicity
Evolu_on
Amplitude Bias

[Constant]...

Decline Rate
Intrinsic Color[Halo]
Non-Standard
Color [I-Band]...
4.515 MeV @[M(core) = 0.451 M(solar][Non-Variable]

First Principles

Standard vs Standardizable Candles
Cepheids

TRGB

Type Ia SNe

MechanicalHeat Engine

StandardCandle

StandardBombPeriod
Temperature
Reddening [Disk]
Metallicity
Evolu_on
Amplitude Bias

[Constant]...

Decline Rate
Intrinsic Color[Halo]
Non-Standard
Color [I-Band]...
4.515 MeV @[M(core) = 0.451 M(solar][Non-Variable]

First Principles

Standard vs Standardizable Candles
Cepheids

TRGB

Type Ia SNe

MechanicalHeat Engine

StandardCandle

Standard
Bomb

PeriodTemperature
Reddening [Disk]
Metallicity
Evolu_on
Amplitude Bias

[Constant]...

Decline Rate
Intrinsic Color[Halo]
Non-Standard
Color [I-Band]...
4.515 MeV @[M(core) = 0.451 M(solar][Non-Variable]

First Principles

A Pulsa_ng Heat Engineversus
A Physical Constant of Nature

Red Giant Branch Evolu_onary Tracks

Electron-Degenerate Helium Core
Mass-Luminosity Rela_on

THERMALRUNAWAYN.B.
No dependence on the total mass of the star.
The hydrogen envelope is just “fuel for the ﬁre”.

TRGB In-Sensi_vity to Progenitor Mass

0.47

A Crisis in Cosmology?

What should
we believe?

First Principles Underwri_ng of theTip of the Red Giant Branch(1) Triple-Alpha process begins the burning of helium at a threshold
temperature of 2 x 108 K (Laboratory Astrophysics, Fowler 1954)(2) That temperature is reached for a core mass of
Mcore = 0.48 Msolar (Core Mass-Luminosity Rela?on)(3) All RGB stars having that core masses simultaneously have the same luminosi_es (Ibid.)(4) A thermal runaway vaporizes the core, lining the degeneracy,
inﬂa_ng the core, collapsing the envelope, and driving the star to
the Horizontal Branch, which 40 _mes fainter than the TRGB.

An astrophysical guillo_ne universally terminates theupward luminosity evolu_on of all red giant branch stars.

Mul_-Wavelength TRGB Sequence
Padova IsochronesMul_-Wavelength TRGB Sequence
Padova Isochrones

A Crisis in Cosmology?

What should
we believe?

LMC Reddening and Calibra_on
M I (TRGB)-4.05 +/- 0.023 mag

LMC (Detached Eclipsing Binary)
Geometric Distance Modulus(m-M)o = 18.477 mag

MASER GALAXY

NGC 4258

Dust & Gas

Young Stars
HaloHalo

Disk

DISK

Disk

Disk

HALO

Major Axis Cepheid Disk Field

Mager et al. 2008

pergianRed Su

Cepheidsts

DISK FIELDBlue Main Sequence Stars

Cepheid Reddening E(V-I) = 0.21 mag

Macri et al. 2006

Maser Galaxy
NGC 4258

Minor Axis
TRGB Halo Field
Mager et al. 2008

HALO FIELD

Pure Halo Fields

SNIa Host Galaxies
TRGB Detec_ons

LMC Calibra_on

TRGB vs Cepheid PrecisionDeconvolu_on of Pair-wise Sca[erDetermina_on of Rela_ve Precision
Indicator
TRGBCepheids
SNe IaVariance
0.0081 mag2
0.0169 mag2
0.0064 mag2

TRGB Method is a factor of 2x more precise(as measured by its variance) than the Cepheids

The Cepheid Calibrators

Cepheid Calibrators in NGC 4258
OpticalInfrared

3”

3”

1”

1”0.5*Sky

Brightest
Contained ValueA Crisis in Cosmology?

What should
we believe?

TRGB

TRGB in IC 1613
The Only Feature Visible in the HaloHa[ et al. 2017

TRGB Halo Fields
No Dust, Controlled Crowding
HaloHalo

TRGB

Disk

TRGB

TRGB
TRGB
TRGB

TRGB
TRGB

TRGB

Hoyt, T. et al. 2019, ApJ 882, 150

TRGB

A Crisis in Cosmology?

What should
we believe?

The PL Rela_on(20 standardiza_on parameters)
••
•
•
•
•
•
•
•

Basic Thermal Physics & Geometry (Sta_c)
Stellar Pulsa_on (P √ ρ )Stellar Excita_on (He+ Instability: Blue Edge)
Stellar De-Excita_on (Convec_on: Red Edge)
Stellar Evolu_on (Bolometric)
Stellar Atmospheres (Shocks, Convec_on, Line Blankeung)
Stellar Composi_on (Interior & Atmospheric)Star Forma_on History (Con_ngent)
Mass Loss (When, Why & How Much?)• Reddening (Foreground & Individual)• Binaries (Calibrators & Targets)• Crowding (Wavelength & Distance Dependent, the “AGB Floor”)

I
N
T
R
I
N
S
ICE
XTR
I
N
SIC

Cepheid Instability Strip in
3 Dimensions
CepheidLow [Fe/H]High [Fe/H]

Higher MassHigherMass

Low Mass

Low Mass

A Crisis in Cosmology?

What should
we believe?

CSP Hubble Diagram
Freedman et al. 2019

Hubble Constant
10:17:57 am
October 5, 2019

Ho = 69.5 +/- 1.7 km/s/Mpc

A Crisis in Cosmology?

What should
we believe?

A Pulsa_ng Heat Engine
versus
A Physical Constant of Nature
Cepheids

TRGB

Closing Case for the TRGB
• Simplicity• Understood with First Principle Physics• Standard Candle• Highest Precision• Zero Point Mul_ply Calibrated Geometrically• Low Reddening• Low Crowding• Applies to all Hubble Types