TDCOSMO. XXIV. Measurement of the Hubble constant from the doubly lensed quasar HE1104-1805

Abstract

Time-delay cosmography leverages strongly lensed quasars to measure the Universe's current expansion rate, H_0, independently from other methods. While the latest TDCOSMO results relied mainly on quadruply lensed quasars, doubly lensed systems are far more common and offer precise time delays, potentially enlarging the usable sample by a factor of five and enabling percent-level constraints on H_0. We present the first TDCOSMO analysis of a doubly imaged source, HE1104-1805, including the measurement of the four necessary ingredients. First, by combining 17 years of data from the SMARTS, Euler and WFI telescopes, we measure a time delay of 176.3\pm 10.8 days. Second, using MUSE data, we extract stellar velocity dispersion measurements in three radial bins with up to 5% precision. Third, employing F160W HST imaging for lens modelling and marginalising over various modelling choices, we measure the Fermat potential difference between the images. Fourth, using wide-field imaging, we measure the convergence added by objects not included in the lens modelling. Hence, we measure the time delay distance and the angular diameter distance to the deflector, favouring a power-law mass model over a baryonic and dark matter composite model. The measurement was performed blindly and yielded H_0 = 64.2^{+5.8}_{-5.0} x $λ_{int} km s^{-1} Mpc^{-1}, where λ_{int} is the internal mass sheet degeneracy parameter. This is in agreement with the TDCOSMO-2025 milestone and its precision for λ_{int}=1 is comparable to that obtained with the best-observed quadruply lensed quasars (4-6%). This work is a stepping stone towards a precise measurement of H_0 using a large sample of doubly lensed quasars, supplementing the current sample. The next TDCOSMO milestone paper will include this system in its hierarchical analysis, constraining λ_{int} and H_0 jointly with multiple lenses.

Figures (21)

• Figure 1: Left panel: Stack of 280 WFI exposures of the field of view used for light curve extraction. Stars nominated PSF1 to PSF5 are used to model the PSF of each exposure and stars designated as N1 to N5 are used to normalise the flux between each exposure. Right panel: HE 1104$-$1805 imaging in the filter F160W band using HST WFC3. The main lensing galaxy is denoted as G, whereas the main perturbers within 5$^{\prime \prime}$ of the lens are numbered from P1 to P9.
• Figure 2: Top panel: HE 1104$-$1805 R-band light curve obtained by joining three datasets: SMARTS (yellow and blue squares), ECAM (purple and green circles) and WFI (brown and pink triangles). For clarity, the light curve of B was shifted by -1.05 mag. The inset zooms on the WFI dataset span, showcasing its superior sampling to the ECAM dataset. Bottom panel: Example of a simultaneous fit of an intrinsic lightcurve with $\eta = 45$ days and $n_{\rm ml} = 15$. The time shift obtained by this fit gives a point estimate of the system's time delay. By repeating such measurements with randomised starting points 800 times, we obtain the time-delay measurement of this ($\eta$, $n_{\rm ml}$) configuration.
• Figure 3: Left panel: Measurements of the time delay for different configurations of ($\eta$, $n_{\rm ml}$) with the merged ECAM+SMART+WFI dataset. Right panel: Measurement of $\Delta t_{\rm AB}$ for the different datasets. Since the datasets overlap, they cannot be considered fully independent. We therefore use our estimate on the joint dataset ECAM+SMARTS+WFI (green data point) as our final estimate. In both panels, the "combined $\tau = 0.5$" value was obtained by marginalising over the measurements listed above it.
• Figure 4: MUSE data cube summed over all wavelengths. The inset displays the point-source subtracted cube revealing the lens galaxy light. The apertures used to extract individual spectra of the quasar images, lens center and perturbers shown in Fig. \ref{['fig:spectra']} are represented by orange circles.
• Figure 5: Velocity dispersion point-estimate in the 3 radial bins of HE 1104$-$1805's lens galaxy. Left panel: Mean of the MUSE data cube after PSF subtraction and masking with overlaid bin numbers and contours. Right panel: Example of a pPXF fit of the integrated spectra of each bin, where data masked for the fit are marked in grey.