H0LiCOW V. New COSMOGRAIL time delays of HE0435-1223: $H_0$ to 3.8% precision from strong lensing in a flat $Λ$CDM model (1607.01790v2)

Abstract: We present a new measurement of the Hubble Constant H0 and other cosmological parameters based on the joint analysis of three multiply-imaged quasar systems with measured gravitational time delays. First, we measure the time delay of HE0435-1223 from 13-year light curves obtained as part of the COSMOGRAIL project. Companion papers detail the modeling of the main deflectors and line of sight effects, and how these data are combined to determine the time-delay distance of HE 0435-1223. Crucially, the measurements are carried out blindly with respect to cosmological parameters in order to avoid confirmation bias. We then combine the time-delay distance of HE0435-1223 with previous measurements from systems B1608+656 and RXJ1131-1231 to create a Time Delay Strong Lensing probe (TDSL). In flat $\Lambda$CDM with free matter and energy density, we find $H_0$ = 71.9 +2.4 -3.0 km/s/Mpc and $\Omega_{\Lambda}$ = 0.62 +0.24 -0.35 . This measurement is completely independent of, and in agreement with, the local distance ladder measurements of H0. We explore more general cosmological models combining TDSL with other probes, illustrating its power to break degeneracies inherent to other methods. The TDSL and Planck joint constraints are $H_0$ = 69.2 +1.4 -2.2 km/s/Mpc, $\Omega_{\Lambda}$ = 0.70 +0.01 -0.01 and $\Omega_k$ = 0.003 +0.004 -0.006 in open $\Lambda$CDM and $H_0$ = 79.0 +4.4 -4.2 km/s/Mpc, $\Omega_{de}$ = 0.77 +0.02 -0.03 and $w$ = -1.38 +0.14 -0.16 in flat $w$CDM. Combined with Planck and Baryon Acoustic Oscillation data, when relaxing the constraints on the numbers of relativistic species we find $N_{eff}$ = 3.34 +0.21 -0.21 and when relaxing the total mass of neutrinos we find 0.182 eV. In an open $w$CDM in combination with Planck and CMB lensing we find $H_0$ = 77.9 +5.0 -4.2 km/s/Mpc, $\Omega_{de}$ = 0.77 +0.03 -0.03, $\Omega_k$ = -0.003 +0.004 -0.004 and $w$ = -1.37 +0.18 -0.23.

• The paper presents time-delay measurements from 13 years of COSMOGRAIL data to determine H0 with 3.8% precision.
• It employs sophisticated, blind lens modeling techniques to minimize biases in cosmological parameter estimation.
• By integrating strong lensing data with CMB observations, the study reinforces the reliability of local H0 estimates in a flat ΛCDM model.

Rigorous Measurements of Hubble Constant via Gravitational Lens Time Delays

The paper "H0LiCOW V. New COSMOGRAIL Time Delays of HE0435: $H_0$ to 3.8% Precision from Strong Lensing in a Flat $\Lambda$CDM Model" presents an in-depth analysis of the Hubble Constant ($H_0$) through observations of multiple lensing systems. The paper is a continuation of the H0LiCOW collaboration's efforts, specifically leveraging data from the COSmological MOnitoring of GRAvItational Lenses (COSMOGRAIL) project. These efforts focus on exploiting the phenomenon of gravitational lensing to provide constraints on cosmological parameters in a manner independent of traditional techniques.

Methodological Advancements

The authors present novel time delay measurements among images of the quasar HE0435-1223 derived from a 13-year-long COSMOGRAIL observation campaign. Accurate time delays in such systems allow for the determination of the so-called time-delay distance, which is primarily sensitive to $H_0$ and weakly dependent on other parameters such as $\Omega_{\Lambda}$ and the equation of state parameter $w$. This paper combines time-delay measurements with sophisticated modeling of the lensing systems, removing biases by conducting blind analyses of the data concerning cosmological parameters.

Key Findings

The paper reports a measured value of $H_0$=71.9_{-3.0}^{+2.4}\ {\rm km\, s^{-1}\,Mpc^{-1}$$with 3.8$$\Omega_m$and energy density$\Omega_{\Lambda}$$. When combining these lensing measurements with Cosmic Microwave Background (CMB) datasets such as those from the Planck mission, robust cosmological constraints emerge. These measurements are consistent with local distance ladder estimations and offer an independent cross-verification.</p> <h3 class='paper-heading' id='implications'>Implications</h3> <p>The determination of$$H_0$ using gravitationally lensed quasars is a significant step forward in cosmology, addressing ongoing tensions between local measurements and CMB-derived values. This paper&#39;s approach helps mitigate degeneracies inherent in other cosmological probes and bolsters confidence in the measured expansion rate of the Universe. Challenges remain in reconciling these values with those derived assuming a strictly cosmological constant ($w = -1$$), given the observed tensions favoring dynamical dark energy components.</p> <h3 class='paper-heading' id='future-directions'>Future Directions</h3> <p>The work suggests the potential for further refinement with additional lenses, improved modeling techniques, and enhanced calibrations. The forthcoming data from further systems in the H0LiCOW collaboration and the STRIDES program promise enhanced accuracy in future atmospheric models and measurements. Moreover, leveraging future technologies like the James Webb Space Telescope (JWST) could yield higher resolution data, further tightening constraints on the mass distribution along the line of sight, and thus refining the inferred time-delay distances. The prospect of handling larger datasets from surveys such as the LSST also suggests that gravitational lensing techniques could provide sub-percent precision on$$H_0$ in the coming years.

In conclusion, this paper underscores the significance of strong lensing as a cosmological tool and the continued need for precise observational campaigns and modeling advancements in astronomy. Moving forward, synergizing various observational techniques will likely be essential in resolving discrepancies in the measured expansion rate of the Universe and offering deeper insights into its fundamental composition and dynamics.