[Paper Review] Lensing results from the Red-sequence Cluster Survey

Henk Hoekstra, H. K. C. Yee+1 more|arXiv (Cornell University)|Jan 31, 2002

Astronomy and Astrophysical Research1 references3 citations

TL;DR

This paper presents weak gravitational lensing measurements from the Red-Sequence Cluster Survey, using galaxies with 19.5 < R_C < 21 as lenses to probe dark matter halo properties. It reports the first robust upper limit on halo truncation scale, s < 470h⁻¹ kpc (99.7% confidence), and finds scale-dependent galaxy biasing with r = 0.57⁺⁰.⁰⁸₋₀.⁰⁷ at ~0.5h⁻¹ Mpc, indicating significant stochastic or non-linear biasing at intermediate scales.

ABSTRACT

We present a variety of weak lensing results based on the ongoing analysis of R_C-band imaging data from the Red-Sequence Cluster Survey (RCS). We briefly discuss the weak lensing signal induced by intervening large scale structure (cosmic shear), and study the properties of the dark matter halos surrounding galaxies with 19.5

Motivation & Objective

• To measure the dark matter halo extent around L* galaxies using weak lensing, addressing the lack of direct constraints on halo truncation.
• To investigate galaxy biasing on small to intermediate scales (0.1–6 h⁻¹ Mpc), where non-linear and stochastic effects may dominate.
• To combine RCS and VIRMOS-DESCART data to separate linear bias (b) and galaxy-mass cross-correlation (r) for the first time in this scale regime.
• To test cosmological models by measuring cosmic shear and comparing with CDM predictions using photometric redshifts.

Proposed method

• Galaxy-galaxy weak lensing is applied to 16.4 deg² of CFHT R_C-band imaging, using R_C = 19.5–21 galaxies as lenses and R_C = 21.5–24 galaxies as sources.
• A parametrized, smoothly truncated halo mass model is used to fit the ensemble-averaged shear signal, enabling constraints on the truncation parameter s.
• Photometric redshift distributions from the Hubble Deep Field North and South are used for source galaxies, while spectroscopic redshifts from CNOC2 constrain lens galaxy redshifts (median z = 0.35).
• Cosmic shear is measured and compared to ΛCDM predictions using σ₈ and Ωₘ parameters, with σ₈ = 0.81⁺⁰.¹⁴₋₀.¹⁹ (95% CL) for Ωₘ = 0.3.
• The bias parameters b and r are measured as functions of scale using a combination of RCS and VIRMOS-DESCART data, with error bars accounting for correlated measurements.
• Likelihood contours are constructed for σ and s to derive joint confidence limits, with the upper limit on s derived under the assumption of a common truncation scale.

Experimental results

Research questions

• RQ1 What is the maximum extent of dark matter halos around L* galaxies, as constrained by weak lensing?
• RQ2 How does the galaxy-mass cross-correlation coefficient r vary with scale, and what does this imply about biasing mechanisms?
• RQ3 To what extent is the bias parameter b scale-dependent for galaxies of luminosity near L*?
• RQ4 How well do cosmic shear measurements from RCS agree with ΛCDM predictions using photometric redshifts?
• RQ5 Can weak lensing distinguish between linear, non-linear, and stochastic biasing at scales of 0.1–6 h⁻¹ Mpc?

Key findings

• The 99.7% confidence upper limit on the truncation parameter is s < 470h⁻¹ kpc, representing the first robust constraint on halo extent from weak lensing.
• The galaxy-mass cross-correlation coefficient r is measured to be r = 0.57⁺⁰.⁰⁸₋₀.⁰⁷ at a scale of ~0.5h⁻¹ Mpc, indicating significant stochastic or non-linear biasing at intermediate scales.
• The bias parameter b increases with scale, rising from b = 0.71⁺⁰.⁰⁶₋₀.⁰⁵ at 0.5–1h⁻¹ Mpc to ~1 on larger scales, suggesting scale-dependent biasing.
• The cosmic shear measurement yields σ₈ = 0.81⁺⁰.¹⁴₋₀.¹⁹ (95% confidence) for a flat Ωₘ = 0.3 model, consistent with prior studies.
• The velocity dispersion of the halos is ⟨σ²⟩¹ᐟ² = 111 ± 5 km/s, consistent with that of L* galaxies.
• The results imply that halos are not fully extended, and the measured r < 1 at ~0.5h⁻¹ Mpc suggests that not all mass is correlated with galaxies at this scale.