At the turn of the last century, measurements of H 0 started converging around H 0 = 70 km s −1 Mpc −1. The Hubble parameter H 0, which describes the current expansion rate of the Universe, has been sought since the discovery in the 1920s that the Universe is expanding (Lemaître 1927 Hubble 1929). Improving the lens modeling uncertainties by a factor of two and a half may reduce the needed sample size to 100 time delays, potentially reachable in the next decade. To reach 1% uncertainty in H 0, we estimate that a sample size of order of 620 time delay measurements of similar quality as those from SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745 would be needed. Combining the six time delays measured in the three cluster-lensed quasars gives H 0 = 74.1 ± 8.0 km s −1 Mpc −1. While a single time delay measurement does not yield a well-constrained H 0 value, analyzing the systems together tightens the constraint. Using the three quasars strongly lensed by galaxy clusters (SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745) that have both multiband Hubble Space Telescope data and published time delay measurements, we derive H 0, accounting for the systematic and statistical sources of uncertainty. To date, Refsdal's method has mostly been applied to quasars lensed by individual galaxies rather than by galaxy clusters. A promising alternative, proposed by Refsdal in 1964, relies on the inverse scaling of H 0 with the delay between the arrival times of at least two images of a strongly lensed variable source such as a quasar. Tension between cosmic microwave background–based and distance ladder–based determinations of the Hubble constant H 0 motivates the pursuit of independent methods that are not subject to the same systematic effects.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |