Keywords

The Carnegie-Chicago Hubble Program (CCHP) is building a direct path to the Hubble constant (H₀) using Population II stars as the calibrator of the Type Ia supernova (SN Ia)-based distance scale. This path to calibrate the SNe Ia is independent of the systematics in the traditional Cepheid-based technique. In this paper, we present the distance to M101, the host to SN 2011fe, using the I-band tip of the red giant branch (TRGB) based on observations from the ACS/WFC instrument on the Hubble Space Telescope. The CCHP targets the halo of M101, where there is little to no host galaxy dust, the red giant branch is isolated from nearly all other stellar populations, and there is virtually no source confusion or crowding at the magnitude of the tip. Applying the standard procedure for the TRGB method from the other works in the CCHP series, we find a foreground-extinction-corrected M101 distance modulus of μ₀ = 29.07 ± 0.04_stat ± 0.05_sys mag, which corresponds to a distance of D = 6.52 ± 0.12_stat ± 0.15_sys Mpc. This result is consistent with several recent Cepheid-based determinations, suggesting agreement between Population I and II distance scales for this nearby SN Ia host galaxy. We further analyze four archival data sets for M101 that have targeted its outer disk to argue that targeting in the stellar halo provides much more reliable distance measurements from the TRGB method owing to the combination of multiple structural components and heavy population contamination. Application of the TRGB in complex regions will have sources of uncertainty not accounted for in commonly used uncertainty measurement techniques.

The cosmic distance duality relation (CDDR) is a fundamental rule in cosmological studies. Given the redshift z, it relates luminosity distance D^L with angular diameter distance D^A through ${(1+z)}^{2}{D}^{A}/{D}^{L}\equiv 1$. Many efforts have been made to test CDDR with various observational approaches. However, to the best of our knowledge, those methods are always affected by cosmic opacity, which could violate CDDR owing to the non-conservation of photon number. Such a mechanism is more related to astroparticle physics. In this work, in order to directly study the nature of spacetime, i.e., to disentangle it from astroparticle physics, we propose a new strategy to test CDDR, with strong lensing providing D^A and gravitational waves (GWs) providing D^L. It is known that the propagation of GWs is unaffected by cosmic opacity. We demonstrate that distances from observations of optical lensing are also opacity-free. These two kinds of distance measurements make it possible to test spacetime. Our results show that the constraints on the deviations of CDDR will be very competitive with current techniques.

Strongly lensed quasars with time-delay measurements are well known to provide the "time-delay distances" ${D}_{{\rm{\Delta }}t}=(1+{z}_{L}){D}_{L}{D}_{S}/{D}_{{LS}}$, and the angular diameter distances to the lens galaxies D_L. These two kinds of distances give stringent constraints on cosmological parameters. In this work, we explore a different use of time-delay observables: under the assumption of a flat universe, strong lensing observations can accurately measure the angular diameter distances to the sources D_S. The corresponding redshifts of the quasars may be up to z_S ∼ 4 according to the forecast. The high-redshift distances would sample the Hubble diagram between SNe Ia and the cosmic microwave background, model-independently providing direct information on the evolution of the nature of our universe, for example, the dark energy equation of state parameter w(z). We apply our method to the existing lensing system SDSS 1206+4332 and get ${D}_{S}={2388}_{-978}^{+2632}\,\mathrm{Mpc}$ at z_S = 1.789. We also make a forecast for the era of Large Synoptic Survey Telescope. The uncertainty of D_S depends on the redshifts of the lens and the source, the uncertainties of D_Δt and D_L, and the correlation between D_Δt and D_L. Larger correlation would result in tighter D_S determination.

We determine the distances to the Type Ia supernova host galaxies M66 (NGC 3627) and M96 (NGC 3368) of the Leo I Group using the Tip of the Red Giant Branch (TRGB) method. We target the stellar halos of these galaxies using the Hubble Space Telescope ACS/WFC in the F606W and F814W bandpasses. By pointing to the stellar halos we sample RGB stars predominantly of Population II, minimize host-galaxy reddening, and significantly reduce the effects of source crowding. Our absolute calibration of the I-band TRGB is based on a recent detached eclipsing binary distance to the Large Magellanic Cloud. With this geometric zero-point in hand, we find for M66 and M96, respectively, true distance moduli μ₀ = 30.23 ± 0.04 (stat) ± 0.06 (sys) mag and μ₀ = 30.29 ± 0.02 (stat) ± 0.06 (sys) mag.

We present a new and independent determination of the local value of the Hubble constant based on a calibration of the tip of the red giant branch (TRGB) applied to Type Ia supernovae (SNe Ia). We find a value of H₀ = 69.8 ± 0.8 (±1.1% stat) ± 1.7 (±2.4% sys) km s⁻¹ Mpc⁻¹. The TRGB method is both precise and accurate and is parallel to but independent of the Cepheid distance scale. Our value sits midway in the range defined by the current Hubble tension. It agrees at the 1.2σ level with that of the Planck Collaboration et al. estimate and at the 1.7σ level with the Hubble Space Telescope (HST) SHoES measurement of H₀ based on the Cepheid distance scale. The TRGB distances have been measured using deep HST Advanced Camera for Surveys imaging of galaxy halos. The zero-point of the TRGB calibration is set with a distance modulus to the Large Magellanic Cloud of 18.477 ± 0.004 (stat) ± 0.020 (sys) mag, based on measurement of 20 late-type detached eclipsing binary stars, combined with an HST parallax calibration of a 3.6 μm Cepheid Leavitt law based on Spitzer observations. We anchor the TRGB distances to galaxies that extend our measurement into the Hubble flow using the recently completed Carnegie Supernova Project I ( CSP-I ) sample containing about 100 well-observed SNe Ia . There are several advantages of halo TRGB distance measurements relative to Cepheid variables; these include low halo reddening, minimal effects of crowding or blending of the photometry, only a shallow (calibrated) sensitivity to metallicity in the I band, and no need for multiple epochs of observations or concerns of different slopes with period. In addition, the host masses of our TRGB host-galaxy sample are higher, on average, than those of the Cepheid sample, better matching the range of host-galaxy masses in the CSP-I distant sample and reducing potential systematic effects in the SNe Ia measurements.

We present a model-independent measurement of spatial curvature Ω_k in the Friedmann–Lemaître–Robertson–Walker universe, based on observations of the Hubble parameter H(z) using cosmic chronometers, and a Gaussian process (GP) reconstruction of the H ii galaxy Hubble diagram. We show that the imposition of spatial flatness (i.e., Ω_k = 0) easily distinguishes between the Hubble constant measured with Planck and that based on the local distance ladder. We find an optimized curvature parameter ${{\rm{\Omega }}}_{k}=-{0.120}_{-0.147}^{+0.168}$ when using the former (i.e., ${H}_{0}=67.66\pm 0.42\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$), and ${{\rm{\Omega }}}_{k}=-{0.298}_{-0.088}^{+0.122}$ for the latter (${H}_{0}=73.24\pm 1.74\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$). The quoted uncertainties are extracted by Monte Carlo sampling, taking into consideration the covariances between the function and its derivative reconstructed by GP. These data therefore reveal that the condition of spatial flatness favors the Planck measurement, while ruling out the locally inferred Hubble constant as a true measure of the large-scale cosmic expansion rate at a confidence level of ∼3σ.

The tip of the red giant branch (TRGB) is a well-established standard candle used to measure distances to nearby galaxies. The TRGB luminosity is typically measured in the I-band, where the luminosity has little dependency on stellar age or stellar metallicity. As the TRGB is brighter at wavelengths redder than the I-band, observational gains can be made if the TRGB luminosity can be robustly calibrated at longer wavelengths. This is of particular interest given the infrared capabilities that will be available with the James Webb Space Telescope and an important calibration consideration for using TRGB distances as part of an independent measurement of the Hubble constant. Here, we use simulated photometry to investigate the dependency of the TRGB luminosity on stellar age and metallicity as a function of wavelength (λ 475 nm–4.5 μm). We find intrinsic variations in the TRGB magnitude to increase from a few hundredths of a magnitude at λ800–900 nm to ∼0.6 mag by λ1.5 μm. We show that variations at the longer infrared wavelengths can be reduced to 0.02−0.05 mag (1%–2% accuracy in distance) with careful calibrations that account for changes in age and metal content. These represent the minimum uncertainties; observational uncertainties will be higher. Such calibration efforts may also provide independent constraints of the age and metallicity of stellar halos where TRGB distances are best measured. At 3.6 and 4.5 μm, the TRGB magnitude is predicted to vary by ∼0.15 mag even after corrections, making these wavelengths less suitable for precision distances.

We perform forecasts for how baryon acoustic oscillation (BAO) scale and redshift-space distortion (RSD) measurements from future spectroscopic emission line galaxy surveys such as Euclid are degraded in the presence of spectral line misidentification. Using analytic calculations verified with mock galaxy catalogs from lognormal simulations, we find that constraints are degraded in two ways, even when the interloper power spectrum is modeled correctly in the likelihood. First, there is a loss of signal-to-noise ratio for the power spectrum of the target galaxies, which propagates to all cosmological constraints and increases with contamination fraction, f_c. Second, degeneracies can open up between f_c and cosmological parameters. In our calculations, this typically increases BAO scale uncertainties at the 10%–20% level when marginalizing over parameters determining the broadband power spectrum shape. External constraints on f_c or parameters determining the shape of the power spectrum, for example, from cosmic microwave background measurements, can remove this effect. There is a near-perfect degeneracy between f_c and the power spectrum amplitude for low f_c values, where f_c is not well determined from the contaminated sample alone. This has the potential to strongly degrade RSD constraints. The degeneracy can be broken with an external constraint on f_c, for example, from cross-correlation with a separate galaxy sample containing the misidentified line or deeper subsurveys.

We present the first attempt at measuring the baryonic acoustic oscillations (BAOs) in the large-scale cross-correlation between the magnesium-II doublet (Mg ii) flux transmission field and the position of quasar and galaxy tracers. The Mg ii flux transmission continuous field at 0.3 < z < 1.6 is measured from 500,589 quasar spectra obtained in the Baryonic Oscillation Spectroscopic Survey (BOSS) and the extended BOSS (eBOSS). The positions of 246,697 quasar tracers and 1346,776 galaxy tracers are extracted from the Sloan Digital Sky Survey I and II, BOSS, and eBOSS catalogs. In addition to measuring the cosmological BAO scale and the biased matter density correlation, this study allows tests and improvements to cosmological Lyα analyses. A feature consistent with that of the BAOs is detected at a significance of Δχ² = 7.25. The measured Mg ii linear transmission bias parameters are b_{Mg ii(2796)} (z = 0.59) = (−6.82 ± 0.54) × 10⁻⁴ and b_{Mg ii(2804)} (z = 0.59) = (−5.55 ± 0.46) ×10⁻⁴, and the Mg i bias is b_{Mg i(2853)} (z = 0.59) = (−1.48 ± 0.24) × 10⁻⁴. Their redshift evolution is characterized by the power-law index: γ_Mg = 3.36 ± 0.46. These measurements open a new window toward using BAOs from flux transmission at z < 1 in the final eBOSS sample and in the upcoming sample from the Dark Energy Spectroscopic Instrument.

We propose a new method for probing the time variation of the effective Newton's constant G_eff, based on the optimal redshift weighting scheme, and demonstrate the efficacy using the DESI galaxy spectroscopic survey. We find that with the optimal redshift weights, the evolution of ${G}_{\mathrm{eff}}(z)$ can be significantly better measured: the uncertainty of ${G}_{\mathrm{eff}}(z)$ can be reduced by a factor of 2.2 ∼ 12.8 using the DESI Bright Galaxy Survey sample at z ≲ 0.45, and by a factor of 1.3 ∼ 4.4 using the DESI Emission Line Galaxies sample covering 0.65 ≲ z ≲ 1.65.