Cepheid Calibration Research Articles

The Near-infrared Extinction Law at High and Low Galactic Latitudes

The Milky Way dust extinction curve in the near-infrared (NIR) follows a power-law form, but the value of the slope, β NIR, is debated. Systematic variations in the slope of the Milky Way UV extinction curve are known to be correlated with variations in the optical slope (through R V ), but whether such a dependence extends to the NIR is unclear. Finally, because of low dust column densities, the NIR extinction law is poorly understood at high Galactic latitudes where most extragalactic work takes place. In this paper, we construct extinction curves from 56,649 stars with Sloan Digital Sky Survey (SDSS) and Two Micron All Sky Survey photometry, based on stellar parameters from SDSS spectra. We use dust maps to identify dust-free stars, from which we calibrate the relation between stellar parameters and intrinsic colors. Furthermore, to probe the low-dust regime at high latitudes, we use aggregate curves based on many stars. We find no systematic variation of β NIR across low-to-moderate dust columns (0.02 < E(B − V) ≲ 1), and report average β NIR = 1.85 ± 0.01, in agreement with the law in the 2019 Fitzpatrick et al. study, but steeper than the Cardelli et al. and 1999 Fitzpatrick laws. Star-to-star scatter in β NIR is relatively small (σ(β NIR) = 0.13). We also find no intrinsic correlation between β NIR and R V (there is an apparent correlation that is the result of the correlated uncertainties in the two values). These results hold for typical sightlines; we do not probe very dusty regions near the Galactic Center, nor rare sightlines with R V > 4. Finally, we find R H = 0.345 ± 0.007 and comment on its bearing on Cepheid calibrations and the determination of H 0.

Connecting Infrared Surface Brightness Fluctuation Distances to Type Ia Supernova Hosts: Testing the Top Rung of the Distance Ladder

We compare infrared surface brightness fluctuation (IR SBF) distances measured in galaxies that have hosted type Ia supernovae (SNe Ia) to distances estimated from SNe Ia light-curve fits. We show that the properties of the SNe Ia found in IR SBF hosts are very different from those exploding in Cepheid calibrators, therefore this is a direct test of systematic uncertainties on the estimation of the Hubble constant (H 0) using SNe. The IR SBF results from Jensen et al. provide a large and uniformly measured sample of IR SBF distances which we directly compare with the distances to 25 SN Ia host galaxies. We divide the Hubble flow SNe Ia into subsamples that best match the divergent SN properties seen in the IR SBF hosts and Cepheid hosts. We further divide the SNe Ia into a sample with light-curve widths and host masses that are congruent to those found in the SBF-calibrated hosts. We refit the light-curve stretch and color correlations with luminosity, and use these revised parameters to calibrate a sample of “Hubble flow” SNe Ia with IR SBF calibrators. Relative to the Hubble flow sample, the average calibrator distance moduli vary by 0.03 mag depending on the SN Ia subsample examined and this adds a 1.8% systematic uncertainty to our Hubble constant estimate. Based on the IRSBF calibrators, H 0 = 74.6 ± 0.9(stat) ± 2.7(syst) km s−1 Mpc−1, which is consistent with the Hubble constant derived from SNe Ia calibrated from Cepheid variables. We conclude that IR SBFs provide reliable calibration of SNe Ia with a precision comparable to Cepheid calibrators, and with a significant saving in telescope time.

Investigating the Hubble tension: Effect of cepheid calibration

Recent observations of Type Ia supernovae (SNe) by SH0ES collaboration (R11 and R16) diverge from the value reported by recent CMBR observations utilising the Planck satellite and application of the ΛCDM cosmological model by at least 3σ. It is among the most challenging problems in contemporary cosmology and is known as the Hubble tension. The SNe Ia in R11 and R16 were calibrated through cepheid variables in three distinct galaxies: Milky Way, LMC, and NGC4258. Carnegie Hubble Program (CHP) observations of type Ia SNe calibrated using the tip of the red giant approach yielded a somewhat different estimate for the Hubble constant. This decreased the Hubble tension from over 3σ to below 2σ. It is a legitimate question to answer whether there are any issues with SNe Ia calibration and to investigate whether the Hubble tension is real or not. We use statistical techniques namely, ANOVA, K-S test, and t-test to examine whether the cepheid calibration is host-dependent. Our analysis shows that (i) both R11 and R16 data suffer from non-Gaussian systematic effects, (ii) H0 values in the sub-samples (different anchor-based) in both R11 and R16 groups are significantly different at a 99% confidence level, and (iii) neglecting the metal-rich MW sample does not reduce the H0 value significantly, and thus Hubble tension persists. A small reduction in the Hubble constant could be linked to the differences in the host environment. Hence instead of using a single universal relation environment based slope and zero point should be preferred.

Sensitivity of the Hubble Constant Determination to Cepheid Calibration

Motivated by the large observed diversity in the properties of extragalactic extinction by dust, we reanalyze the Cepheid calibration used to infer the Hubble constant, H 0, from Type Ia supernovae, using Cepheid data in 19 Type Ia supernova host galaxies from Riess et al. and anchor data from Riess et al. Unlike the SH0ES team, we do not enforce a fixed universal color–luminosity relation to correct the Cepheid magnitudes. Instead, we focus on a data-driven method, where the optical colors and near-infrared magnitudes of the Cepheids are used to derive individual color–luminosity relations for each Type Ia supernova host and anchor galaxy. We present two different analyses, one based on Wesenheit magnitudes, resulting in H 0 = 73.2 ± 1.3 km s−1 Mpc−1, a 4.2σ tension with the value inferred from the cosmic microwave background. In the second approach, we calibrate an individual extinction law for each galaxy, with noninformative priors using color excesses, yielding H 0 = 73.9 ± 1.8 km s−1 Mpc−1, in 3.4σ tension with the Planck value. Although the two methods yield similar results, in the latter approach, the Hubble constants inferred from the individual Cepheid absolute distance calibrator galaxies range from H 0 = 68.1 ± 3.5 km s−1 Mpc−1 to H 0 = 76.7 ± 2.0 km s−1 Mpc−1. Taking the correlated nature of H 0 inferred from individual anchors into account, and allowing for individual extinction laws, the Milky Way anchor is in 2.1–3.1 σ tension with the NGC 4258 and Large Magellanic Cloud anchors, depending on prior assumptions regarding the color–luminosity relations and the method used for quantifying the tension.

Late-transition versus smooth H(z) -deformation models for the resolution of the Hubble crisis

Gravitational transitions at low redshifts ($z_t<0.1$) have been recently proposed as a solution to the Hubble and growth tensions. Such transitions would naturally lead to a transition in the absolute magnitude $M$ of type Ia supernovae (SnIa) at $z_t$ (Late $M$ Transitions - $LMT$) and possibly in the dark energy equation of state parameter $w$ (Late $w-M$ Transitions - $LwMT$). Here, we compare the quality of fit to cosmological data of this class of models, with the corresponding quality of fit of the cosmological constant model ($\Lambda$CDM) and some of the best smooth $H(z)$ deformation models ($w$CDM, CPL, PEDE). We also perform model selection via the Akaike Information Criterion and the Bayes factor. We use the full CMB temperature anisotropy spectrum data, the baryon acoustic oscillations (BAO) data, the Pantheon SnIa data, the SnIa absolute magnitude $M$ as determined by Cepheid calibrators and the value of the Hubble constant $H_0$ as determined by local SnIa calibrated using Cepheids. We find that smooth $H(z)$ deformation models perform worse than transition models for the following reasons: 1) They have a worse fit to low-$z$ geometric probes (BAO and SnIa data); 2) They favor values of the SnIa absolute magnitude $M$ that are lower as compared to the value $M_c$ obtained with local Cepheid calibrators at $z<0.01$; 3) They tend to worsen the $\Omega_\mathrm{m,0}-\sigma_\mathrm{8,0}$ growth tension. We also find that the $w-M$ transition model ($LwMT$) does not provide a better quality of fit to cosmological data than a pure $M$ transition model ($LMT$) where $w$ is fixed to the \lcdm value $w=-1$ at all redshifts. We conclude that the $LMT$ model has significant statistical advantages over smooth late-time $H(z)$ deformation models in addressing the Hubble crisis.

Hubble tension or a transition of the Cepheid SnIa calibrator parameters?

We re-analyze the Cepheid data used to infer the value of $H_0$ by calibrating SnIa. We do not enforce a universal value of the empirical Cepheid calibration parameters $R_W$ (Cepheid Wesenheit color-luminosity parameter) and $M_H^{W}$ (Cepheid Wesenheit H-band absolute magnitude). Instead, we allow for variation of either of these parameters for each individual galaxy. We also consider the case where these parameters have two universal values: one for low galactic distances $D<D_c$ and one for high galactic distances $D>D_c$ where $D_c$ is a critical transition distance. We find hints for a $3\sigma$ level mismatch between the low and high galactic distance parameter values. We then use AIC and BIC criteria to compare and rank the following types of models: Base models: Universal values for $R_W$ and $M_H^{W}$ (no parameter variation), I Individual fitted galactic $R_W$ with a universal fitted $M_H^{W}$, II Universal fixed $R_W$ with individual fitted galactic $M_H^{W}$, III Universal fitted $R_W$ with individual fitted galactic $M_H^{W}$, IV Two universal fitted $R_W$ (near and far) with one universal fitted $M_H^{W}$, V Universal fitted $R_W$ with two universal fitted $M_H^{W}$ (near and far), VI Two universal fitted $R_W$ with two universal fitted $M_H^{W}$ (near and far). We find that the AIC and BIC criteria consistently favor model IV instead of the commonly used Base model where no variation is allowed for the Cepheid empirical parameters. The best fit value of the SnIa absolute magnitude $M_B$ and of $H_0$ implied by the favored model IV is consistent with the inverse distance ladder calibration based on the CMB sound horizon $H_0=67.4\pm 0.5\,km\,s^{-1}\,Mpc^{-1}$. Thus in the context of the favored model IV the Hubble crisis is not present. This model may imply the presence of a fundamental physics transition taking place at a time more recent than $100\,Myrs$ ago.

Measurements of the Hubble Constant: Tensions in Perspective*

Abstract Measurement of the distances to nearby galaxies has improved rapidly in recent decades. The ever-present challenge is to reduce systematic effects, especially as greater distances are probed and the uncertainties become larger. In this paper, we combine several recent calibrations of the tip of the red giant branch (TRGB) method. These calibrations are internally self-consistent at the 1% level. New Gaia Early Data Release 3 data provide an additional consistency check at a (lower) 5% level of accuracy, a result of the well-documented Gaia angular covariance bias. The updated TRGB calibration applied to a sample of Type Ia supernovae from the Carnegie Supernova Project results in a value of the Hubble constant of H 0 = 69.8 ± 0.6 (stat) ± 1.6 (sys) km s−1 Mpc−1. No statistically significant difference is found between the value of H 0 based on the TRGB and that determined from the cosmic microwave background. The TRGB results are also consistent to within 2σ with the SHoES and Spitzer plus Hubble Space Telescope (HST) Key Project Cepheid calibrations. The TRGB results alone do not demand additional new physics beyond the standard (ΛCDM) cosmological model. They have the advantage of simplicity of the underlying physics (the core He flash) and small systematic uncertainties (from extinction, metallicity, and crowding). Finally, the strengths and weaknesses of both the TRGB and Cepheids are reviewed, and prospects for addressing the current discrepancy with future Gaia, HST, and James Webb Space Telescope observations are discussed. Resolving this discrepancy is essential for ascertaining if the claimed tension in H 0 between the locally measured and CMB-inferred values is physically motivated.

The Hubble Tension, the M Crisis of Late Time H(z) Deformation Models and the Reconstruction of Quintessence Lagrangians

We present a detailed and pedagogical analysis of recent cosmological data, including CMB, BAO, SnIa and the recent local measurement of H0. We thus obtain constraints on the parameters of these standard dark energy parameterizations, including ΛCDM, and H(z) deformation models such as wCDM (constant equation of state w of dark energy), and the CPL model (corresponding to the evolving dark energy equation-of-state parameter w(z)=w0+waz1+z). The fitted parameters include the dark matter density Ω0m, the SnIa absolute magnitude M, the Hubble constant H0 and the dark energy parameters (e.g., w for wCDM). All models considered lead to a best-fit value of M that is inconsistent with the locally determined value obtained by Cepheid calibrators (M tension). We then use the best-fit dark energy parameters to reconstruct the quintessence Lagrangian that would be able to reproduce these best-fit parameterizations. Due to the derived late phantom behavior of the best-fit dark energy equation-of-state parameter w(z), the reconstructed quintessence models have a negative kinetic term and are therefore plagued with instabilities.

W−M phantom transition at zt&lt;0.1 as a resolution of the Hubble tension

A rapid phantom transition of the dark energy equation of state parameter $w$ at a transition redshift ${z}_{t}&lt;0.1$ of the form $w(z)=\ensuremath{-}1+\mathrm{\ensuremath{\Delta}}w\text{ }\mathrm{\ensuremath{\Theta}}({z}_{t}\ensuremath{-}z)$ with $\mathrm{\ensuremath{\Delta}}w&lt;0$ can lead to a higher value of the Hubble constant while closely mimicking a $\mathrm{Planck}18/\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ form of the comoving distance $r(z)={\ensuremath{\int}}_{0}^{z}\frac{d{z}^{\ensuremath{'}}}{H({z}^{\ensuremath{'}})}$ for $z&gt;{z}_{t}$. Such a transition however would imply a significantly lower value of the SnIa absolute magnitude $M$ than the value ${M}_{C}$ imposed by local Cepheid calibrators at $z&lt;0.01$. Thus, in order to resolve the ${H}_{0}$ tension it would need to be accompanied by a similar transition in the value of the SnIa absolute magnitude $M$ as $M(z)={M}_{C}+\mathrm{\ensuremath{\Delta}}M\text{ }\mathrm{\ensuremath{\Theta}}(z\ensuremath{-}{z}_{t})$ with $\mathrm{\ensuremath{\Delta}}M&lt;0$. This is a late $w\ensuremath{-}M$ phantom transition ($LwMPT$). It may be achieved by a sudden reduction of the value of the normalized effective Newton constant $\ensuremath{\mu}={G}_{\mathrm{eff}}/{G}_{\mathrm{N}}$ by about 6% assuming that the absolute luminosity of SnIa is proportional to the Chandrasekhar mass which varies as ${\ensuremath{\mu}}^{\ensuremath{-}3/2}$. We demonstrate that such an ultra low $z$ abrupt feature of $w\ensuremath{-}M$ provides a better fit to cosmological data compared to smooth late time deformations of $H(z)$ that also address the Hubble tension. For ${z}_{t}=0.02$ we find $\mathrm{\ensuremath{\Delta}}w\ensuremath{\simeq}\ensuremath{-}4$, $\mathrm{\ensuremath{\Delta}}M\ensuremath{\simeq}\ensuremath{-}0.1$. This model also addresses the growth tension due to the predicted lower value of $\ensuremath{\mu}$ at $z&gt;{z}_{t}$. A prior of $\mathrm{\ensuremath{\Delta}}w=0$ (no $w$ transition) can still resolve the ${H}_{0}$ tension with a larger amplitude $M$ transition with $\mathrm{\ensuremath{\Delta}}M\ensuremath{\simeq}\ensuremath{-}0.2$ at ${z}_{t}\ensuremath{\simeq}0.01$. This implies a larger reduction of $\ensuremath{\mu}$ for $z&gt;0.01$ (about 12%). The $LwMPT$ can be generically induced by a scalar field nonminimally coupled to gravity with no need of a screening mechanism since in this model $\ensuremath{\mu}=1$ at $z&lt;0.01$.

Cosmic Distances Calibrated to 1% Precision with Gaia EDR3 Parallaxes and Hubble Space Telescope Photometry of 75 Milky Way Cepheids Confirm Tension with ΛCDM

Abstract We present an expanded sample of 75 Milky Way Cepheids with Hubble Space Telescope (HST) photometry and Gaia EDR3 parallaxes, which we use to recalibrate the extragalactic distance ladder and refine the determination of the Hubble constant. All HST observations were obtained with the same instrument (WFC3) and filters (F555W, F814W, F160W) used for imaging of extragalactic Cepheids in Type Ia supernova (SN Ia) hosts. The HST observations used the WFC3 spatial scanning mode to mitigate saturation and reduce pixel-to-pixel calibration errors, reaching a mean photometric error of 5 millimags per observation. We use new Gaia EDR3 parallaxes, greatly improved since DR2, and the period–luminosity (P–L) relation of these Cepheids to simultaneously calibrate the extragalactic distance ladder and to refine the determination of the Gaia EDR3 parallax offset. The resulting geometric calibration of Cepheid luminosities has 1.0% precision, better than any alternative geometric anchor. Applied to the calibration of SNe Ia, it results in a measurement of the Hubble constant of 73.0 ± 1.4 km s−1 Mpc−1, in good agreement with conclusions based on earlier Gaia data releases. We also find the slope of the Cepheid P–L relation in the Milky Way, and the metallicity dependence of its zero-point, to be in good agreement with the mean values derived from other galaxies. In combination with the best complementary sources of Cepheid calibration, we reach 1.8% precision and find H 0 = 73.2 ± 1.3 km s−1 Mpc−1, a 4.2σ difference with the prediction from Planck CMB observations under ΛCDM. We expect to reach ∼1.3% precision in the near term from an expanded sample of ∼40 SNe Ia in Cepheid hosts.

The value of the Hubble–Lemaître constant queried by Type Ia supernovae: a journey from the Calán-Tololo Project to the Carnegie Supernova Program

ABSTRACT We assess the robustness of the two highest rungs of the ‘cosmic distance ladder’ for Type Ia supernovae and the determination of the Hubble–Lemaître constant. In this analysis, we hold fixed Rung 1 as the distance to the LMC determined to 1 per cent using detached eclipsing binary stars. For Rung 2, we analyse two methods, the TRGB and Cepheid distances for the luminosity calibration of Type Ia supernovae in nearby galaxies. For Rung 3, we analyse various modern digital supernova samples in the Hubble flow, such as the Calán-Tololo, CfA, CSP, and Supercal data sets. This metadata analysis demonstrates that the TRGB calibration yields smaller H0 values than the Cepheid calibration, a direct consequence of the systematic difference in the distance moduli calibrated from these two methods. Selecting the three most independent possible methodologies/bandpasses (B, V, J), we obtain H0 = 69.9 ± 0.8 and H0= 73.5 ± 0.7 $\, \rm km\, s^{-1} \, Mpc^{-1}$from the TRGB and Cepheid calibrations, respectively. Adding in quadrature the systematic uncertainty in the TRGB and Cepheid methods of 1.1 and 1.0 $\, \rm km\, s^{-1} \, Mpc^{-1}$, respectively, this subset reveals a significant 2.0σ systematic difference in the calibration of Rung 2. If Rung 1 and Rung 2 are held fixed, the different formalisms developed for standardizing the supernova peak magnitudes yield consistent results, with a standard deviation of 1.5 $\, \rm km\, s^{-1} \, Mpc^{-1}$, that is, Type Ia supernovae are able to anchor Rung 3 with 2 per cent precision. This study demonstrates that Type Ia supernovae have provided a remarkably robust calibration of R3 for over 25 yr.

Low-redshift measurement of the sound horizon through gravitational time-delays

Context. The matter sound horizon can be infered from the cosmic microwave background within the Standard Model. Independent direct measurements of the sound horizon are then a probe of possible deviations from the Standard Model. Aims. We aim at measuring the sound horizon rs from low-redshift indicators, which are completely independent of CMB inference. Methods. We used the measured product H(z)rs from baryon acoustic oscillations (BAO) together with supernovae Ia to constrain H(z)/H0 and time-delay lenses analysed by the H0LiCOW collaboration to anchor cosmological distances (∝ H0−1). Additionally, we investigated the influence of adding a sample of quasars with higher redshift with standardisable UV-Xray luminosity distances. We adopted polynomial expansions in H(z) or in comoving distances so that our inference was completely independent of any cosmological model on which the expansion history might be based. Our measurements are independent of Cepheids and systematics from peculiar motions to within percent-level accuracy. Results. The inferred sound horizon rs varies between (133 ± 8) Mpc and (138 ± 5) Mpc across different models. The discrepancy with CMB measurements is robust against model choice. Statistical uncertainties are comparable to systematics. Conclusions. The combination of time-delay lenses, supernovae, and BAO yields a distance ladder that is independent of cosmology (and of Cepheid calibration) and a measurement of rs that is independent of the CMB. These cosmographic measurements are then a competitive test of the Standard Model, regardless of the hypotheses on which the cosmology is based.

Local resolution of the Hubble tension: The impact of screened fifth forces on the cosmic distance ladder

The discrepancy between the values of the Hubble constant $H_0$ derived from the local distance ladder and the cosmic microwave background provides a tantalising hint of new physics. We explore a potential resolution involving screened fifth forces in the local Universe, which alter the Cepheid calibration of supernova distances. In particular, if the Cepheids with direct distance measurements from parallax or water masers are screened but a significant fraction of those in other galaxies are not, neglecting the difference between their underlying period--luminosity relations biases the local $H_0$ measurement high. This difference derives from a reduction in the Cepheid pulsation period and possible increase in luminosity under a fifth force. We quantify the internal and environmental gravitational properties of the Riess et al. distance ladder galaxies to assess their degrees of screening under a range of phenomenological models, and propagate this information into the $H_0$ posterior as a function of fifth force strength. We consider well-studied screening models in scalar--tensor gravity theories such as chameleon, K-mouflage and Vainshtein, along with a recently-proposed mechanism based on baryon--dark matter interactions in which screening is governed by local dark matter density. We find that a fifth force strength $\sim5-30\%$ that of gravity can alleviate (though not resolve) the $H_0$ tension in some scenarios, around the sensitivity level at which tests based on other distance ladder data can constrain this strength. Although our analysis is exploratory and based on screening models not necessarily realised in full theories, our results demonstrate that new physics-based local resolutions of the $H_0$ tension are possible, supplementing those already known in the pre-recombination era.

Think Global, Act Local: The Influence of Environment Age and Host Mass on Type Ia Supernova Light Curves

Abstract The reliability of Type Ia Supernovae (SNe Ia) may be limited by the imprint of their galactic origins. To investigate the connection between supernovae and their host characteristics, we developed an improved method to estimate the stellar population age of the host as well as the local environment around the site of the supernova. We use a Bayesian method to estimate the star formation history and mass weighted age of a supernova’s environment by matching observed spectral energy distributions to a synthesized stellar population. Applying this age estimator to both the photometrically and spectroscopically classified Sloan Digital Sky Survey II supernovae (N = 103), we find a 0.114 ± 0.039 mag “step” in the average Hubble residual at a stellar age of ∼8 Gyr; it is nearly twice the size of the currently popular mass step. We then apply a principal component analysis on the SALT2 parameters, host stellar mass, and local environment age. We find that a new parameter, PC1, consisting of a linear combination of stretch, host stellar mass, and local age, shows a very significant (4.7σ) correlation with Hubble residuals. There is a much broader range of PC1 values found in the Hubble flow sample when compared with the Cepheid calibration galaxies. These samples have mildly statistically different average PC1 values, at ∼2.5σ, resulting in at most a 1.3% reduction in the evaluation of H 0. Despite accounting for the highly significant trend in SN Ia Hubble residuals, there remains a 9% discrepancy between the most recent precision estimates of H 0 using SN Ia and the CMB.

Gaia Cepheid parallaxes and ‘Local Hole’ relieve H0 tension

ABSTRACT There is an ≈9 ± 2.5 per cent tension between the value of Hubble’s Constant, H0 = 67.4 ± 0.5 km s−1 Mpc−1, implied by the Planck microwave background power spectrum and that given by the distance scale of H0 = 73.4 ± 1.7 km s−1Mpc−1. But with a plausible assumption about a Gaia DR2 parallax systematic offset, we find that Gaia parallax distances of Milky Way Cepheid calibrators are ≈12–15 per cent longer than previously estimated. Similarly, Gaia also implies ≈4.7 ± 1.7 per cent longer distances for 46 Cepheids than previous distances on the scale of Riess et al. Then we show that the existence of an ≈150 h−1Mpc ‘Local Hole’ in the galaxy distribution implies an outflow of ≈500 km s−1. Accounting for this in the recession velocities of SNIa standard candles out to z ≈ 0.15 reduces H0 by a further ≈1.8 per cent. Combining the above two results would reduce the distance scale H0 estimate by ≈7 per cent from H0 ≈ 73.4 ± 1.7 to ≈68.9 ± 1.6 km s−1Mpc−1, in reasonable agreement with the Planck value. We conclude that the discrepancy between distance scale and Planck H0 measurements remains unconfirmed due to uncertainties caused by Gaia systematics and an unexpectedly inhomogeneous local galaxy distribution.

Insensitivity of the distance ladder Hubble constant determination to Cepheid calibration modelling choices

Recent determination of the Hubble constant via Cepheid-calibrated supernovae by \citet{riess_2.4_2016} (R16) find $\sim 3\sigma$ tension with inferences based on cosmic microwave background temperature and polarization measurements from $Planck$. This tension could be an indication of inadequacies in the concordance $\Lambda$CDM model. Here we investigate the possibility that the discrepancy could instead be due to systematic bias or uncertainty in the Cepheid calibration step of the distance ladder measurement by R16. We consider variations in total-to-selective extinction of Cepheid flux as a function of line-of-sight, hidden structure in the period-luminosity relationship, and potentially different intrinsic color distributions of Cepheids as a function of host galaxy. Considering all potential sources of error, our final determination of $H_0 = 73.3 \pm 1.7~{\rm km/s/Mpc}$ (not including systematic errors from the treatment of geometric distances or Type Ia Supernovae) shows remarkable robustness and agreement with R16. We conclude systematics from the modeling of Cepheid photometry, including Cepheid selection criteria, cannot explain the observed tension between Cepheid-variable and CMB-based inferences of the Hubble constant. Considering a `model-independent' approach to relating Cepheids in galaxies with known distances to Cepheids in galaxies hosting a Type Ia supernova and finding agreement with the R16 result, we conclude no generalization of the model relating anchor and host Cepheid magnitude measurements can introduce significant bias in the $H_0$ inference.

THE TIP OF THE RED GIANT BRANCH DISTANCES TO TYPE IA SUPERNOVA HOST GALAXIES. III. NGC 4038/39 AND NGC 5584

We present the tip of the red giant branch (TRGB) distances to Type Ia supernova (SNe Ia) host galaxies NGC 4038/39 and NGC 5584. Based on the deep images constructed using archival Hubble Space Telescope data, we detect red giant branch stars in each galaxy. VI photometry of the resolved stars and corresponding I-band luminosity functions show the TRGB to be at I_{TRGB} = 27.67 \pm 0.05 for NGC 4038/39 and I_{TRGB} = 27.77 \pm 0.04 for NGC 5584. From these estimates, we determine the distance modulus to NGC 4038/39 to be (m-M)_0 = 31.67 \pm 0.05 (random) \pm 0.12 (systematic) (corresponding to a linear distance of 21.58 \pm 0.50 \pm 1.19 Mpc) and the distance modulus to NGC 5584 to be (m-M)_0 = 31.76 \pm 0.04 (random) \pm 0.12 (systematic) (corresponding to a linear distance of 22.49 \pm 0.41 \pm 1.24 Mpc). We derive a mean absolute maximum magnitude of SNe Ia of M_V = -19.29 \pm 0.08 from the distance estimates of five SNe Ia (including two SNe in this study and three SNe Ia from our previous studies), and we derive a value of M_V = -19.19 \pm 0.10 using three low-reddened SNe Ia among the five SNe Ia. With these estimates, we derive a value of the Hubble constant, H_0 = 69.8 \pm 2.6 (random) \pm 3.9 (systematic) km/s/Mpc and 72.2 \pm 3.3 (random) \pm 4.0 (systematic) km/s/Mpc, respectively. The value from the five SNe is similar to those from the cosmic microwave background analysis, and not much different within errors, from those of recent Cepheid calibrations of SNe Ia. The value from the three SNe is between the values from the two methods.

THE TIP OF THE RED GIANT BRANCH DISTANCES TO TYPE Ia SUPERNOVA HOST GALAXIES. II. M66 AND M96 IN THE LEO I GROUP

M66 and M96 in the Leo I Group are nearby spiral galaxies hosting Type Ia Supernovae (SNe Ia). We estimate the distances to these galaxies from the luminosity of the tip of the red giant branch (TRGB). We obtain $VI$ photometry of resolved stars in these galaxies from $F555W$ and $F814W$ images in the {\it Hubble Space Telescope} archive. From the luminosity function of these red giants we find the TRGB $I$-band magnitude to be $I_{\rm TRGB}=26.20\pm0.03$ for M66 and $26.21\pm0.03$ for M96. These values yield distance modulus $(m-M)_0=30.12\pm0.03 ({\rm random})\pm0.12 ({\rm systematic})$ for M66 and $(m-M)_0=30.15\pm0.03 ({\rm random})\pm0.12 ({\rm systematic})$ for M96. These results show that they are indeed the members of the same group. With these results we derive absolute maximum magnitudes of two SNe (SN 1989B in M66 and SN 1998bu in M96). $V$-band magnitudes of these SNe Ia are $\sim$0.2 mag fainter than SN 2011fe in M101, the nearest recent SN Ia. We also derive near-infrared magnitudes for SN 1998bu. Optical magnitudes of three SNe Ia (SN 1989B, SN 1998bu, and SN 2011fe) based on TRGB analysis yield a Hubble constant, $H_0=67.6\pm1.5 ({\rm random})\pm 3.7({\rm systematic})$ \kmsMpc. This value is similar to the values derived from recent WMAP9 results, $H_0=69.32\pm0.80$ \kmsMpc. % and from Planck results, $H_0=67.3\pm1.2$ \kmsMpc, but smaller than other recent determinations based on Cepheid calibration for SNe Ia luminosity, $H_0 = 74 \pm3$ km s$^{-1}$ Mpc$^{-1}$.

ANCHORING THE DISTANCE SCALE VIA X-RAY/INFRARED DATA FOR CEPHEID CLUSTERS: SU Cas

New X-ray (XMM-Newton) and JHKs (OMM) observations for members of the star cluster Alessi 95, which Turner et al.(2012) discovered hosts the classical Cepheid SU Cas, were used in tandem with UCAC3 (proper motion) and 2MASS observations to determine precise cluster parameters: E(J-H)=0.08+-0.02 and d=405+-15 pc. The ensuing consensus among cluster, pulsation, IUE, and trigonometric distances (d=414+-5(se)+-10(sd) pc) places SU Cas in a select group of nearby fundamental Cepheid calibrators (Delta Cep, Zeta Gem). High-resolution X-ray observations may be employed to expand that sample as the data proved pertinent for identifying numerous stars associated with SU Cas. Acquiring X-ray observations of additional fields may foster efforts to refine Cepheid calibrations used to constrain H_0.

NEW EVIDENCE SUPPORTING CLUSTER MEMBERSHIP FOR THE KEYSTONE CALIBRATOR DELTA CEPHEI

New and existing UBVJHKs, spectroscopic, NOMAD, HST, and revised HIP observations are employed to determine properties for delta Cep and its host star cluster. The multi-faceted approach ensured that uncertainties were mitigated (~2%). The following fundamental parameters were inferred for delta Cep: E(B-V)=0.073+-0.018, log(t)=7.9+-0.1, and d=272+-3(se)+-5(sd) pc. The cluster exhibits a turnoff near B6 (M*/Ms~5), and the brightest host cluster members are the supergiants zeta Cep (K1.5Ib) and delta Cep. To within the uncertainties, the two stars share common astrometric parameters (pi, mu_ra, mu_dec, RV\sim-17 km/s) and are tied to bluer members via the evolutionary track implied by the cluster's UBVJHKs color-color and color-magnitude diagrams. The cluster's existence is bolstered by the absence of an early-type sequence in color-magnitude diagrams for comparison fields. NOMAD data provided a means to identify potential cluster members (n~30) and double the existing sample. That number could increase with forthcoming precise proper motions (DASCH) for fainter main-sequence stars associated with classical Cepheids (e.g., delta Cep), which may invariably foster efforts to strengthen the Galactic Cepheid calibration and reduce uncertainties tied to H_0.