We present the first detection of a gravitational depletion signal at near-infrared wavelengths , based on deep panoramic images of the cluster Abell 2219 ( z =0.22 ) taken with the Cambridge Infrared Survey Instrument ( CIRSI ) at the prime focus of the 4.2m William Herschel Telescope .
Infrared studies of gravitational depletion offer a number of advantages over similar techniques applied at optical wavelengths , and can provide reliable total masses for intermediate redshift clusters .
Using the maximum likelihood technique developed by Schneider , King & Erben ( 1999 ) , we detect the gravitational depletion at the 3 \sigma confidence level .
By modeling the mass distribution as a singular isothermal sphere and ignoring the uncertainty in the unlensed number counts , we find an Einstein radius of \theta _ { E } \simeq 13.7 ^ { +3.9 } _ { -4.2 } arcsec ( 66 % confidence limit ) .
This corresponds to a projected velocity dispersion of \sigma _ { v } \sim 800 km s ^ { -1 } , in agreement with constraints from strongly-lensed features .
For a Navarro , Frenk and White mass model , the radial dependence observed indicates a best-fitting halo scale length of 125 h ^ { -1 } kpc .
We investigate the uncertainties arising from the observed fluctuations in the unlensed number counts , and show that clustering is the dominant source of error .
We extend the maximum likelihood method to include the effect of incompleteness , and discuss the prospects of further systematic studies of lensing in the near-infrared band .