THE SURPRISINGLY STEEP MASS PROFILE OF A1689, FROM A LENSING ANALYSIS OF SUBARU IMAGES

摘要

Subaru observations of A1689 (z = 0.183) are used to derive an accurate, model-independent mass profile for the entire cluster, r approx< 2 Mpc h~(-1), by combining magnification bias and distortion measurements. The projected mass profile steepens quickly with increasing radius, falling away to zero at r ～ 1.0 Mpc h~(-1), well short of the anticipated virial radius. Our profile accurately matches the inner profile, r approx< 200 kpc h~(-1), derived from deep Hubble Space Telescope Advanced Camera for Surveys (ACS) images. The combined ACS and Subaru information is well fitted by a Navarro-Frenk-White profile with virial mass, (1.93 ± 0.20) x 10~(15) solar mass, and surprisingly high concentration, c_(vir) = 13.7_(-1.1)~(+1.4), significantly larger than theoretically expected (c_(vir) approx= 4), corresponding to a relatively steep overall profile. A slightly better fit is achieved with a steep power-law model, d log ∑(θ)/d log θ approx= -3, with a core θ_c approx= 1.7′ (r_c approx= 210 kpc h~(-1)), whereas an isothermal profile is strongly rejected. These results are based on a reliable sample of background galaxies selected to be redder than the cluster E/SO sequence. By including the faint blue galaxy population, a much smaller distortion signal is found, demonstrating that blue cluster members significantly dilute the true signal for r approx< 400 kpc h~(-1). This contamination is likely to affect most weak lensing results to date.