Lens Environments as Laboratories for Galaxy Evolution

Publication Title

NOAO Proposal ID 2006B-0553

Document Type



Poor groups are the most common environments for galaxies, and thus are important laboratories for studying galaxy evolution. Unfortunately, little is known about groups at redshifts 〉 0.1, because of the difficulty in identifying them in the first place. Our survey of the environments of strong gravitational lenses is yielding surprising results: more than 50% of lenses lie in groups or clusters of galaxies and at least 10-50% of lenses have massive structures superposed along the line-of-sight that alter the cosmological constraints derived from lens models in excess of the published errors. The resulting large, homogeneous sample of intermediate redshift groups is unparalleled to date and provides a means to constrain the evolution of groups and their members from z ~ 0.5 to the present epoch. Our previous spectroscopic work targeted mostly the red sequences identified via our photometry of lens fields. While this approach was a efficient way to find dense lens environments, it excluded the bluest and reddest galaxies by definition, as well as undersampling interloping structures. Given these biases, it is difficult to fully characterize the evolution of groups in our sample and the lensing contributions from structures fore and aft of the lens. Here we propose to fix this incompleteness and finalize our survey by obtaining 90 % complete, color-unbiased spectroscopy for I_*+1.2 and brighter galaxies within 1.5 virial radii of six previously observed lenses.


Physics and Astronomy



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