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Analytic Analysis of Galaxy Projection along Line of Sight

This research presents an analytic approach to assess galaxy projection effects along a line of sight, utilizing a halo model and tuning parameters to match data from the Sloan Digital Sky Survey (SDSS). Predictions on projection effects are made via Monte Carlo simulations, with future directions focusing on high redshift, the M-N relation, and velocity dispersion corrections.

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Analytic Analysis of Galaxy Projection along Line of Sight

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  1. An Analytic Approachto Assess Galaxy ProjectionAlong A Line of Sight Anbo Chen University of Michigan

  2. In Collaboration • University of Michigan • Gus Evrard, Jiangang Hao, Tim Mckay • University of Chicago • Matt Becker

  3. Outline • Building a halo model to assess the projection effect • Tuning model parameters to SDSS • Making predictions on expected projection effect • Monte Carlo realizations and applications • Future directions

  4. Building the Analytic Model • Initial power spectrum (Eisenstein & Hu) • Halo-halo correlation (Seljak & Warren) • HOD (Brown et al.) • N(M,z,MB)~(M-Mmin)/Mscale • Color Model (Hao et al.) • G-R mean and sigma for Red and Blue galaxies • Blue fraction in central and satellite galaxies

  5. The Current Color Model

  6. The Color Model (Ctd.) • z~0.6 turn around is not currently well characterized • Crucial on background projections from Red population

  7. Mean Projection Effect Targeting on a dark matter halo (cluster) and calculate the expected projection of galaxies

  8. Projection from Different Epoch

  9. Sensitivity to Magnitude Limit

  10. Comparison to SDSS M-N200 Relationship • Johnston et al. (right panel) has slope = 1.28 +/- 0.04 • Consistent only considering projection effect

  11. Monte Carlo Simulation • Method • Calculate the probability of finding a halo within each volume in space and mass • Calculate the probability of having a galaxy in each volume in N-dim space • Application • Distribution of contamination • Velocity dispersion

  12. Realization in Color Diagram

  13. Application to Velocity Dispersion • The analytic model can help interpret the non-Gaussianity in velocity dispersion and henceforth put corrections on the velocity dispersion

  14. Conclusion • An analytic model built to address the projection effect along line of sight • Parameters tuned to the result from SDSS • Expected projection predicted with cluster size and magnitude limit • Application via Monte Carlo method • Future directions • high redshift • M-N relation • velocity dispersion

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