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Register a new userThe Accuracy of the Hubble Constant Measurement Verified through Cepheid Amplitudes
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The accuracy of the Hubble constant measured with extragalactic Cepheids depends on robust photometry and background estimation in the presence of stellar crowding. The conventional approach accounts for crowding by sampling backgrounds near Cepheids and assuming they match those at their positions. We show a direct consequence of crowding by unresolved sources at Cepheid sites is a reduction in the fractional amplitudes of their light curves. We use a simple analytical expression to infer crowding directly from the light curve amplitudes of >200 Cepheids in 3 SNe~Ia hosts and NGC 4258 as observed by HST -- the first near-infrared amplitudes measured beyond the Magellanic Clouds. Where local crowding is minimal, we find near-infrared amplitudes match Milky Way Cepheids at the same periods. At greater stellar densities we find that the empirically measured amplitudes match the values predicted (with no free parameters) from crowding assessed in the conventional way from local regions, confirming their accuracy for estimating the background at the Cepheid locations. Extragalactic Cepheid amplitudes would need to be ~20% smaller than measured to indicate additional, unrecognized crowding as a primary source of the present discrepancy in H_0. Rather we find the amplitude data constrains a systematic mis-estimate of Cepheid backgrounds to be 0.029 +/- 0.037 mag, more than 5x smaller than the size of the present ~0.2 mag tension in H_0. We conclude that systematic errors in Cepheid backgrounds do not provide a plausible resolution to the Hubble tension.
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Motivated by the large observed diversity in the properties of extra-galactic extinction by dust, we re-analyse the Cepheid calibration used to infer the local value of the Hubble constant, $H_0$, from Type Ia supernovae. Unlike the SH0ES team, we do not enforce a universal color-luminosity relation to correct the near-IR Cepheid magnitudes. Instead, we focus on a data driven method, where the measured colors of the Cepheids are used to derive a color-luminosity relation for each galaxy individually. We present two different analyses, one based on Wesenheit magnitudes, a common practice in the field that attempts to combine corrections from both extinction and variations in intrinsic colors, resulting in $H_0=66.9pm 2.5$ km/s/Mpc, in agreement with the Planck value. In the second approach, we calibrate using color excesses with respect to derived average intrinsic colors, yielding $H_0=71.8pm 1.6$ km/s/Mpc, a $2.7,sigma$ tension with the value inferred from the cosmic microwave background. Hence, we argue that systematic uncertainties related to the choice of Cepheid color-luminosity calibration method currently inhibits us from measuring $H_0$ to the precision required to claim a substantial tension with Planck data.
Strong gravitational lensing has been a powerful probe of cosmological models and gravity. To date, constraints in either domain have been obtained separately. We propose a new methodology through which the cosmological model, specifically the Hubble constant, and post-Newtonian parameter can be simultaneously constrained. Using the time-delay cosmography from strong lensing combined with the stellar kinematics of the deflector lens, we demonstrate the Hubble constant and post-Newtonian parameter are incorporated in two distance ratios which reflect the lensing mass and dynamical mass, respectively. Through the reanalysis of the four publicly released lenses distance posteriors from the H0LiCOW collaboration, the simultaneous constraints of Hubble constant and post-Newtonian parameter are obtained. Our results suggests no deviation from the General Relativity, $gamma_{texttt{PPN}}=0.87^{+0.19}_{-0.17}$ with a Hubble constant favors the local Universe value, $H_0=73.65^{+1.95}_{-2.26}$ km s$^{-1}$ Mpc$^{-1}$. Finally, we forecast the robustness of gravity tests by using the time-delay strong lensing for constraints we expect in the next few years. We find that the joint constraint from 40 lenses are able to reach the order of $7.7%$ for the post-Newtonian parameter and $1.4%$ for Hubble constant.
This is the first of two papers reporting measurements from a program to determine the Hubble constant to 5% precision from a refurbished distance ladder. We present new observations of 110 Cepheid variables in the host galaxies of two recent Type Ia supernovae (SNe Ia), NGC 1309 and NGC 3021, using the Advanced Camera for Surveys on the Hubble Space Telescope (HST). We also present new observations of the hosts previously observed with HST whose SNe Ia provide the most precise luminosity calibrations: SN 1994ae in NGC 3370, SN 1998aq in NGC 3982, SN 1990N in NGC 4639, and SN 1981B in NGC 4536, as well as the maser host, NGC 4258. Increasing the interval between observations enabled the discovery of new, longer-period Cepheids, including 57 with P>60 days, which extend these period-luminosity (PL) relations. We present 93 measurements of the metallicity parameter, 12 + log[O/H], measured from HII regions in the vicinity of the Cepheids and show these are consistent with solar metallicity. We find the slope of the seven dereddened PL relations to be consistent with that of the Large Magellanic Cloud Cepheids and with parallax measurements of Galactic Cepheids, and we address the implications for the Hubble constant. We also present multi-band light curves of SN 2002fk (in NGC 1309) and SN 1995al (in NGC 3021) which may be used to calibrate their luminosities. In the second paper we present observations of the Cepheids in the H-band obtained with the Near Infrared Camera and Multi-Object Spectrometer on HST, further mitigating systematic errors along the distance ladder resulting from dust and chemical variations. The quality and homogeneity of these SN and Cepheid data provide the basis for a more precise determination of the Hubble constant.
Progressive increases in the precision of the Hubble-constant measurement via Cepheid-calibrated Type Ia supernovae (SNe Ia) have shown a discrepancy of $sim 4.4sigma$ with the current value inferred from Planck satellite measurements of the cosmic microwave background radiation and the standard $Lambda$CDM cosmological model. This disagreement does not appear to be due to known systematic errors and may therefore be hinting at new fundamental physics. Although all of the current techniques have their own merits, further improvement in constraining the Hubble constant requires the development of as many independent methods as possible. In this work, we use SNe II as standardisable candles to obtain an independent measurement of the Hubble constant. Using 7 SNe II with host-galaxy distances measured from Cepheid variables or the tip of the red giant branch, we derive H$_0= 75.8^{+5.2}_{-4.9}$ km s$^{-1}$ Mpc$^{-1}$ (statistical errors only). Our value favours that obtained from the conventional distance ladder (Cepheids + SNe Ia) and exhibits a difference of 8.4 km s$^{-1}$ Mpc$^{-1}$ from the Planck $+Lambda$CDM value. Adding an estimate of the systematic errors (2.8 km s$^{-1}$ Mpc$^{-1}$) changes the $sim 1.7sigma$ discrepancy with Planck $+Lambda$CDM to $sim 1.4sigma$. Including the systematic errors and performing a bootstrap simulation, we confirm that the local H$_0$ value exceeds the value from the early Universe with a confidence level of 95%. As in this work we only exchange SNe II for SNe Ia to measure extragalactic distances, we demonstrate that there is no evidence that SNe Ia are the source of the H$_0$ tension.
Two sources of geometric information are encoded in the galaxy power spectrum: the sound horizon at recombination and the horizon at matter-radiation equality. Analyzing the BOSS DR12 galaxy power spectra using perturbation theory with $Omega_m$ priors from Pantheon supernovae but no priors on $Omega_b$, we obtain constraints on $H_0$ from the second scale, finding $H_0 = 65.1^{+3.0}_{-5.4},mathrm{km},mathrm{s}^{-1}mathrm{Mpc}^{-1}$; this differs from the best-fit of SH0ES at 95% confidence. Similar results are obtained if $Omega_m$ is constrained from uncalibrated BAO: $H_0 = 65.6^{+3.4}_{-5.5},mathrm{km},mathrm{s}^{-1}mathrm{Mpc}^{-1}$. Adding the analogous lensing results from Baxter & Sherwin 2020, the posterior shifts to $70.6^{+3.7}_{-5.0},mathrm{km},mathrm{s}^{-1}mathrm{Mpc}^{-1}$. Using mock data, Fisher analyses, and scale-cuts, we demonstrate that our constraints do not receive significant information from the sound horizon scale. Since many models resolve the $H_0$ controversy by adding new physics to alter the sound horizon, our measurements are a consistency test for standard cosmology before recombination. A simple forecast indicates that such constraints could reach $sigma_{H_0} simeq 1.6,mathrm{km},mathrm{s}^{-1}mathrm{Mpc}^{-1}$ in the era of Euclid.
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