Blending and obscuration in weak-lensing magnification

E. Gaztanaga, S. J. Schmidt, M. D. Schneider, J. A. Tyson

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We test the impact of some systematic errors in weak-lensing (WL) magnification measurements with the COSMOS 30-band photo-z Survey flux limited to Iauto < 25.0 using correlations of both source galaxy counts and magnitudes. Systematic obscuration effects are measured by comparing counts and magnification correlations. We use the Advanced Camera for Survey-Hubble Space Telescope catalogues to identify potential blending objects (close pairs) and perform the magnification analyses with and without blended objects. We find that blending effects start to be important (∼0.04-mag obscuration) at angular scales smaller than 0.1 arcmin. Extinction and other systematic obscuration effects can be as large as 0.10 mag (U band) but are typically smaller than 0.02 mag depending on the band. After applying these corrections, we measure a 3.9σ magnification signal that is consistent for both counts and magnitudes. The corresponding projected mass profiles of galaxies at redshift z R 0.6 (MI R -21) is ς = 25 ± 6 Mpdbl h3 pc-2 at 0.1 Mpc h-1, consistent with NFW type profile with M200 R 2 × 1012 Mpdblh pc-2. Tangential shear and flux-size magnification over the same lenses show similar mass profiles. We conclude that magnification from counts and fluxes using photometric redshifts has the potential to provide complementary WL information in future wide-field surveys once we carefully take into account systematic effects, such as obscuration and blending.

Original languageEnglish
Pages (from-to)4964-4975
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date25 Feb 2021
Publication statusPublished - 1 May 2021


  • gravitational lensing: weak
  • large-scale structure of Universe
  • methods: observational

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