The surprisingly steep mass profile of A1689, from a lensing analysis of Subaru images

Subaru observations of A1689 (z = 0.183) are used to derive an accurate, model-independent mass profile for the entire cluster, r less than or similar to 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 similar to 1.0 Mpc h(-1), well short of the anticipated virial radius. Our profile accurately matches the inner profile, r less than or similar to 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) M-. and surprisingly high concentration c(vir) = 13.7(-1.1)(+1.4), significantly larger than theoretically expected (c(vir) similar or equal to 4), corresponding to a relatively steep overall profile. A slightly better fit is achieved with a steep power-law model, d log Sigma(theta)/d log theta similar or equal to -3, with a core theta(c) similar or equal to 1.'7 (r(c) similar or equal to 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/S0 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 less than or similar to 400 kpc h(-1). This contamination is likely to affect most weak lensing results to date.