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Context.Time-delay cosmography uses strong gravitational lensing of a time-variable source to infer the Hubble constant. The measurement is independent from both traditional distance ladder and CMB measurements. An accurate measurement with this technique requires considering the effects of objects along the line of sight outside the primary lens, which is quantified by the external convergence (κext). In absence of such corrections,H0will be biased towards higher values in overdense fields and lower values in underdense fields. Aims.We discuss the current state of the methods used to account for environment effects. We present a new software package built for this kind of analysis and others that can leverage large astronomical survey datasets. We apply these techniques to the SDSS J0924+0219 strong lens field. Methods.We infer the relative density of the SDSS J0924+0219 field by computing weighted number counts for all galaxies in the field, and comparing to weighted number counts computed for a large number of fields in a reference survey. We then compute weighted number counts in the Millennium Simulation and compare these results to infer the external convergence of the lens field. Results.Our results show the SDSS J0924+0219 field is a fairly typical line of sight, with medianκext = −0.012 and standard deviationσκ = 0.028.
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Testing the Strong Equivalence Principle. II. Relating the External Field Effect in Galaxy Rotation Curves to the Large-scale Structure of the Universe
Abstract Theories of modified gravity generically violate the strong equivalence principle, so that the internal dynamics of a self-gravitating system in freefall depends on the strength of the external gravitational field (the external field effect). We fit rotation curves (RCs) from the SPARC database with a model inspired by Milgromian dynamics (MOND), which relates the outer shape of an RC to the external Newtonian field from the large-scale baryonic matter distribution through a dimensionless parametereN. We obtain a > 4σstatistical detection of the external field effect (i.e.eN> 0 on average), confirming previous results. We then locate the SPARC galaxies in the cosmic web of the nearby universe and find a striking contrast in the fittedeNvalues for galaxies in underdense versus overdense regions. Galaxies in an underdense region between 22 and 45 Mpc from the celestial axis in the northern sky have RC fits consistent witheN≃ 0, while those in overdense regions adjacent to the CfA2 Great Wall and the Perseus−Pisces Supercluster returneNthat are a factor of two larger than the median for SPARC galaxies. We also calculate independent estimates ofeNfrom galaxy survey data and find that they agree with theeNinferred from the RCs within the uncertainties, the chief uncertainty being the spatial distribution of baryons not contained in galaxies or clusters.
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- Award ID(s):
- 1911909
- PAR ID:
- 10306025
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 921
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 104
- Size(s):
- Article No. 104
- Sponsoring Org:
- National Science Foundation
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