2012/04/30 by J. Blazek, Jonathan Blazek, Rachel Mandelbaum +3 · 85 citations
Physics and Astronomy · #Adaptive optics and wavefront sensing #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Cosmology #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy formation and evolution #Gravitational lens #Photometric redshift #Physics #Redshift #Sky #Strong gravitational lensing #Weak gravitational lensing #astro-ph.CO
paper · pdf · doi:10.1088/1475-7516/2012/05/041
published in Journal of Cosmology and Astroparticle Physics 2012(05), 041 (Institute of Physics) · 31 pages, 8 Figures. Minor changes to reflect published version
arxiv created 2012/05/31 · openalex publication_date 2012/05/31 · arxiv updated 2012/06/04 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The coherent physical alignment of galaxies is an important systematic for gravitational lensing studies as well as a probe of the physical mechanisms involved in galaxy formation and evolution. We develop a formalism for treating this intrinsic alignment (IA) in the context of galaxy-galaxy lensing and present an improved method for measuring IA contamination, which can arise when sources physically associated with the lens are placed behind the lens due to photometric redshift scatter. We apply the technique to recent Sloan Digital Sky Survey (SDSS) measurements of Luminous Red Galaxy lenses and typical ( ∼ L * ) source galaxies with photometric redshifts selected from the SDSS imaging data. Compared to previous measurements, this method has the advantage of being fully self-consistent in its treatment of the IA and lensing signals, solving for the two simultaneously. We find an IA signal consistent with zero, placing tight constraints on both the magnitude of the IA effect and its potential contamination to the lensing signal. While these constraints depend on source selection and redshift quality, the method can be applied to any measurement that uses photometric redshifts. We obtain a model-independent upper-limit of roughly 10% IA contamination for projected separations of r p ≈ 0.1–10 h −1 Mpc. With more stringent photo- z cuts and reasonable assumptions about the physics of intrinsic alignments, this upper limit is reduced to 1–2%. These limits are well below the statistical error of the current lensing measurements. Our results suggest that IA will not present intractable challenges to the next generation of galaxy-galaxy lensing experiments, and the methods presented here should continue to aid in our understanding of alignment processes and in the removal of IA from the lensing signal.