$H_0$ Measurements from Time-Delay Strong Lensing
7th lensed system: [1910.06306] STRIDES: A 3.9 per cent measurement of the Hubble constant from the strong lens system DES J0408-5354 | Slide graphic from 7th lens | Poster by Anwar Shajib on 7th lens paper |
Results from 6 lensed systems [1907.04869] H0LiCOW XIII. A 2.4% measurement of $H_{0}$ from lensed quasars: $5.3σ$ tension between early and late-Universe probes “Gravitational lensing offers an independent method of determining H0. When a background object (the “sourceâ€) is gravitationally lensed into multiple images by an intervening mass (the “lensâ€), light rays emitted from the source will take different paths through space-time at the different image positions. Because these paths have different lengths and pass through different gravitational potentials, light rays emitted from the source at the same time will arrive at the observer at different times depending on which image it arrives at. If the source is variable, this “time delay†between multiple images can be measured by monitoring the lens and looking for flux variations corresponding to the same source event. The time delay is related to a quantity referred to as the “time-delay distanceâ€, D∆t, and depends on the mass distribution in the lensing object, the mass distribution along the line of sight (LOS), and cosmological parameters. D∆t is primarily sensitive to H0, although there is a weak dependence on other parameters (e.g., Coe & Moustakas 2009; Linder 2011; Treu & Marshall 2016). This one-step method is completely independent of and complementary to the CMB and the distance ladder. The distances probed by time-delay cosmography are also larger than those from the distance ladder, making this method immune to a monopole in the bulk velocity field of the local Universe (i.e., a 'Hubble bubble')” (excerpt from pg2)
Bonvin et al. (2017) noted that the first three H0LiCOW systems showed a trend of lower lens redshift systems having a larger inferred value of H0, but could not conclude anything due to the small sample size. With a sample of six lenses, we see that this general trend still remains, as well as a trend of decreasing H0 with increasing D∆t. Even with six lenses, these correlations are not significant enough to conclude whether this is a real effect arising from some unknown systematic, a real physical effect related to cosmology, or just a statistical fluke (see Appendix A).
Bonvin 2017 pg12: “Intriguingly, we note that the H0 values yielded by each system individually get larger for lower lens redshifts. So far, we cannot state if this comes from a simple statistical fluke, an unknown systematic error or hints towards an unaccounted physical property. The addition of two more lenses from the H0LiCOW sample will certainly help us in that regard.”
Collaborations: H0LiCOW1 | SHARP2 | STRIDES3 | COSMOGRAIL4 |
“The blind analysis of a seventh lens system using methods very similar to those adopted by H0LiCOW has recently been published by the STRIDES collaboration (Shajib et al. 2019, an independent analysis adopting a different modeling software is currently under way), finding 74.2+2.7−3.0km s−1Mpc−1, in agreement with the H0LiCOW result. This most recent system is particularly interesting since it has two sets of multiple images at different redshifts, which help break some of the degeneracies, and results in the most precise individual measurement so far. In order to make further progress in this important arena, members of the COSMOGRAIL, H0LiCOW, SHARP and STRIDES collaborations interested in time-delay cosmography of lensed quasars have decided to join forces with other scientists and form a new “umbrella” collaboration named TDCOSMO (Time-Delay COSMOgraphy).” [source, pg 2]
[1506.07524] COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses XV. Assessing the achievability and precision of time-delay measurements [1607.00017] H0LiCOW I. $H_0$ Lenses in COSMOGRAIL's Wellspring: Program Overview [1904.07237] Next generation cosmography with strong lensing and stellar dynamics
Other Articles: H0ly Cow! A New Measurement of the Hubble Constant | astrobites Cosmologists Debate How Fast the Universe Is Expanding, Quanta Magazine, by Natalie Wolchover Cosmic Magnifying Glasses Yield Independent Measure of Universe's Expansion Astronomically Rare 'Double Lens' Yields Best Single System Measurement Of Cosmic Expansion A Crisis in Cosmology – W. M. Keck Observatory
Researchers: Sherry Suyu, (MPA, De) Simon Birrer, (Stanford) | github projects | Chris Fassnacht, (UCD) | UC Davis articles | Tomasso Treu (UCLA): presentation at July 2019 KITP conference Lucas Macri, (TAMU) Anowar Shajib, (UCLA) Geoff Chih-Fan Chen, (UCD)
Terms: 1 H0LiCOW: H0 lenses in COSMOGRAIL’s Wellspring 2 SHARP: Strong lensing at High Angular Resolution Program 3 STRIDES: STRong-lensing Insights into Dark Energy Survey 4 COSMOGRAIL: COSmological MOnitoring of GRAvItational Lenses