A comparison of cosmological models using strong gravitational lensing galaxies

Fulvio Melia, Jun Jie Wei, Xue Feng Wu

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


Strongly gravitationally lensed quasar-galaxy systems allow us to compare competing cosmologies as long as one can be reasonably sure of the mass distribution within the intervening lens. In this paper, we assemble a catalog of 69 such systems from the Sloan Lens ACS and Lens Structure and Dynamics surveys suitable for this analysis, and carry out a one-on-one comparison between the standard model, λCDM, and the Rh = ct universe, which has thus far been favored by the application of model selection tools to other kinds of data. We find that both models account for the lens observations quite well, though the precision of these measurements does not appear to be good enough to favor one model over the other. Part of the reason is the so-called bulge-halo conspiracy that, on average, results in a baryonic velocity dispersion within a fraction of the optical effective radius virtually identical to that expected for the whole luminous-dark matter distribution modeled as a singular isothermal ellipsoid, though with some scatter among individual sources. Future work can greatly improve the precision of these measurements by focusing on lensing systems with galaxies as close as possible to the background sources. Given the limitations of doing precision cosmological testing using the current sample, we also carry out Monte Carlo simulations based on the current lens measurements to estimate how large the source catalog would have to be in order to rule out either model at a ∼99.7% confidence level. We find that if the real cosmology is ?CDM, a sample of ∼200 strong gravitational lenses would be sufficient to rule out Rh = ct at this level of accuracy, while ∼300 strong gravitational lenses would be required to rule out ?CDM if the real universe were instead Rh = ct. The difference in required sample size reflects the greater number of free parameters available to fit the data with ?CDM. We point out that, should the Rh = ct universe eventually emerge as the correct cosmology, its lack of any free parameters for this kind of work will provide a remarkably powerful probe of the mass structure in lensing galaxies, and a means of better understanding the origin of the bulge-halo conspiracy.

Original languageEnglish (US)
Article number2
JournalAstronomical Journal
Issue number1
StatePublished - Jan 1 2015


  • cosmology: observations
  • cosmology: theory
  • galaxies: halos
  • galaxies: structure
  • gravitational lensing: strong
  • quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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