Tip of the Red Giant Branch Distances to NGC 1316, NGC 1380, NGC 1404, & NGC 4457: A Pilot Study of a Parallel Distance Ladder Using Type Ia Supernovae in Early-Type Host Galaxies (2508.20023v1)

Abstract: Though type-Ia supernovae (SNe Ia) are found in all types of galaxies, recent local Hubble constant measurements have disfavored using SNe Ia in early-type or quiescent galaxies, aiming instead for better consistency with SNe Ia in star-forming, late-type host galaxies calibrated by Cepheid distances. Here we investigate the feasibility of a parallel distance ladder using SNe Ia exclusively in quiescent, massive ($\log M_*/M_{\odot} \geq 10$) host galaxies, calibrated by tip of the red giant branch (TRGB) distances. We present TRGB measurements to four galaxies: three measured from the Hubble Space Telescope with the ACS F814W filter, and one measured from the JWST NIRCam F090W filter. Combined with literature measurements, we define a TRGB calibrator sample of five high-mass, early-type galaxies that hosted well-measured SNe Ia: NGC 1316 (SN 2006dd), NGC 1380 (SN 1992A), NGC 1404 (SN 2007on, SN 2011iv), NGC 4457 (SN 2020nvb), and NGC 4636 (SN 2020ue). We jointly standardize these calibrators with a fiducial sample of 124 Hubble-flow SNe Ia from the Zwicky Transient Facility that are matched in host-galaxy and light-curve properties. Our results with this homogenized subsample show a Hubble residual scatter of under 0.11 mag, lower than usually observed in cosmological samples of the full SN~Ia distribution. We obtain a measurement of the Hubble constant, $H_0 = 75.3 \pm 2.9$ km s$^{-1}$ Mpc$^{-1}$, including statistical and estimated systematic uncertainties, and discuss the potential to further improve the precision of this approach. As calibrator and supernova samples grow, we advocate that future cosmological applications of SNe Ia use subsamples matched in host-galaxy and supernova properties across redshift.

• The paper demonstrates a parallel distance ladder by calibrating Type Ia supernovae in early-type galaxies using the TRGB method.
• It employs HST and JWST imaging with rigorous photometric cuts and Bayesian analysis, achieving low scatter in distance measurements.
• The approach yields H0 = 75.3 ± 1.7 (stat) ± 2.4 (sys) km s⁻¹ Mpc⁻¹, highlighting improved precision through matched host properties.

Tip of the Red Giant Branch Distances and a Parallel Distance Ladder: A Technical Analysis

Introduction and Motivation

This paper presents a pilot implementation of a parallel distance ladder for measuring the Hubble constant ($H_0$) using Type Ia supernovae (SNe Ia) exclusively in massive, quiescent (early-type) host galaxies, calibrated via the tip of the red giant branch (TRGB) method. The motivation is to construct a distance ladder that is independent of Cepheid variables, which are limited to star-forming galaxies, and to address potential systematics arising from mismatched host-galaxy and supernova properties across the rungs of the traditional distance ladder. The work leverages new and archival HST and JWST imaging to measure TRGB distances to four early-type galaxies (NGC 1316, NGC 1380, NGC 1404, NGC 4457), and combines these with literature data for NGC 4636, all of which have hosted well-observed SNe Ia.

TRGB Distance Measurements: Data, Methods, and Results

The TRGB method exploits the uniform luminosity of low-mass, old red giant stars at the onset of the helium flash, observable as a sharp discontinuity in the color-magnitude diagram (CMD) of resolved stellar populations. The paper utilizes high-fidelity photometric catalogs derived from HST/ACS, HST/WFC3-UVIS, and JWST/NIRCam imaging, with rigorous spatial and quality cuts to mitigate crowding and photometric artifacts.

The spatial selection and crowding analysis for photometric catalog culling is illustrated for NGC 1404, where concentric elliptical annuli are used to identify regions of acceptable crowding for robust TRGB measurement.

Figure 1: High-fidelity photometry catalog culling for NGC 1404, showing spatial annuli and crowding parameter optimization.

For each galaxy, CMDs are constructed from the high-fidelity catalogs, and the TRGB is identified using a Bayesian maximum likelihood approach that models the luminosity function (LF) with explicit terms for RGB and AGB slopes, photometric uncertainties, and completeness corrections from artificial star tests. Color-based metallicity corrections are applied following the quadratic transformation system of Jang & Lee (2017), ensuring consistency across varying stellar populations.

The CMDs and TRGB fits for NGC 1316, NGC 1380, NGC 1404, and NGC 4457 are shown below.

Figure 2: High-fidelity CMD and TRGB fit for NGC 1316, with spatial selection and rejected sources.

Figure 3: CMD and TRGB fit for NGC 1380 using JWST/NIRCam data, demonstrating color-dependent TRGB calibration.

Figure 4: CMD and TRGB fit for NGC 1404, with spatial exclusion of crowded regions and background galaxies.

Figure 5: CMD and TRGB fit for NGC 4457, based on ACS photometry.

The resulting TRGB distance moduli for the four galaxies are:

• NGC 1316: $\mu = 31.50^{+0.06}_{-0.03} \pm 0.04$ mag
• NGC 1380: $\mu = 31.32 \pm 0.03 \pm 0.04$ mag (JWST F090W)
• NGC 1404: $\mu = 31.23^{+0.09}_{-0.07} \pm 0.04$ mag
• NGC 4457: $\mu = 31.12^{+0.01}_{-0.03} \pm 0.04$ mag

These are consistent with, or improve upon, previous literature values, and demonstrate the feasibility of TRGB measurements in early-type galaxies at distances up to $\sim$20 Mpc.

Type Ia Supernova Standardization in Early-Type Hosts

The SNe Ia in the calibrator galaxies (SN 2006dd, SN 1992A, SN 2007on, SN 2011iv, SN 2020nvb, SN 2020ue) are analyzed using both SALT2 and BayeSN light-curve models. The sample is characterized by fast-declining light curves ($x_1 < 0$), reflecting the known correlation between SN Ia properties and host-galaxy environment. The light-curve fits and model comparisons are shown below.

Figure 6: Light-curve fits for the six calibrator SNe Ia, comparing SALT2 and BayeSN models.

Standardization is performed using the Tripp formula, with empirical corrections for light-curve shape ($\alpha$), color ($\beta$), and host-galaxy stellar mass ($\gamma$). The analysis emphasizes the necessity of deriving these coefficients self-consistently for the restricted sample, as their values differ significantly from those obtained for the full SN Ia population.

Hubble-Flow Sample Selection and Joint Standardization

A volume-limited, homogeneous Hubble-flow sample of 124 SNe Ia from the ZTF DR2 is selected to match the calibrator sample in host mass, color, and light-curve properties. Strict cuts are applied: $-2 < x_1 < 0$, $-0.2 < c < +0.1$, $\log M_*/M_\odot > 10$, and $g-z > 1$. The Hubble diagram for this sample, after standardization, exhibits an RMS scatter of 0.106 mag, lower than typical cosmological SN Ia samples.

Figure 7: Hubble diagram and residuals for the ZTF Hubble-flow SNe Ia in massive, quiescent hosts, after standardization.

The standardization coefficients for the matched sample are:

• $\alpha = 0.209 \pm 0.016$ (steeper than typical)
• $\beta = 2.11 \pm 0.17$ (weaker color correction)
• $\gamma = 0.111 \pm 0.029$ mag dex$^{-1}$ (significant host-mass trend)

These trends are visualized below.

Figure 8: Standardization relations for $x_1$, $c$, and host mass, comparing the fiducial and full samples.

Hubble Constant Measurement and Analysis Variants

A joint MCMC fit to the calibrator and Hubble-flow samples yields:

• $H_0 = 75.3 \pm 1.7$ (stat) $\pm 2.4$ (sys) km s$^{-1}$ Mpc$^{-1}$

The standardized absolute magnitudes of the calibrator SNe Ia and their implications for $H_0$ are shown below.

Figure 9: Standardized absolute magnitudes of calibrator SNe Ia and corresponding $H_0$ values.

The posterior distributions for all model parameters are well-constrained.

Figure 10: MCMC corner plot for the joint standardization and $H_0$ inference.

Analysis variants (e.g., including SN 2007on, stricter or looser sample cuts, omitting host-mass correction) are explored, with $H_0$ varying by less than 3% across plausible choices. The inclusion of SN 1994D in NGC 4526, which meets the sample criteria, lowers $H_0$ by 1.1% and further reduces the calibrator scatter.

Implications, Limitations, and Future Prospects

Key findings and implications:

• The parallel TRGB+SNe Ia distance ladder in early-type hosts yields a low-scatter, homogeneous sample, with Hubble residuals ($\sim$0.1 mag) lower than those in traditional mixed-host samples.
• The measured $H_0$ is consistent with other local determinations and remains in tension with the CMB-inferred value at the $\sim$2.7$\sigma$ level.
• The analysis demonstrates that host-galaxy and SN property matching across the distance ladder rungs is critical for minimizing systematics and improving precision.
• The host-mass correction remains significant even within the high-mass regime, suggesting residual environmental dependencies not fully captured by current standardization models.

Limitations:

• The calibrator sample size is small (5–6 SNe Ia), limiting the robustness of scatter and systematics estimates.
• The TRGB zeropoint is anchored in star-forming galaxies, introducing a potential systematic if the TRGB calibration differs in early-type systems.
• The analysis does not apply explicit bias corrections for selection effects, though the volume-limited Hubble-flow sample mitigates this concern.
• The use of SALT2 for fast-declining SNe Ia is suboptimal; alternative models (e.g., BayeSN) may further reduce scatter.

Future directions:

• JWST and future facilities (e.g., Roman, Habitable Worlds Observatory) will enable TRGB measurements in a much larger volume, increasing the calibrator sample and extending the method to greater distances.
• Cross-calibration with surface-brightness fluctuation (SBF) distances and further integration with hierarchical Bayesian models will refine the approach.
• The methodology of matched subsample selection should be adopted in all SN Ia cosmology analyses to control for evolving progenitor and host properties with redshift.

Conclusion

This pilot paper demonstrates the feasibility and advantages of a parallel distance ladder using TRGB-calibrated SNe Ia in massive, quiescent galaxies. The approach yields a low-scatter, homogeneous sample and a precise measurement of $H_0$, with systematics controlled by strict matching of host and SN properties. The results underscore the importance of sample homogeneity in distance ladder cosmology and provide a framework for future expansion as larger samples and deeper TRGB measurements become available.