2018/04/30 by Liang Dai, Tejaswi Venumadhav, Alexander A. Kaurov +1 · 1 citation
Physics and Astronomy · #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/aae478
15 pages and 8 figures including references. Version 3: matching manuscript accepted by ApJ; Figure 8 corrected; conclusions unchanged
arxiv created 2018/10/13 · arxiv updated 2018/11/07
Luminous stars in background galaxies straddling the lensing caustic of a foreground galaxy cluster can be individually detected due to extreme magnification factors of ∼ 102--103, as recently observed in deep HST images. We propose a direct method to probe the presence of dark matter subhalos in galaxy clusters by measuring the astrometric perturbation they induce on the image positions of magnified stars or bright clumps: lensing by subhalos breaks the symmetry of a smooth critical curve, traced by the midpoints of close image pairs. For the giant arc at z = 0.725 behind the lensing cluster Abell 370 at z = 0.375, a promising target for detecting image pairs of stars, we find that subhalos of masses in the range 106--108 M_\odot with the abundance predicted in the cold dark matter theory should typically imprint astrometric distortions at the level of 20--80 \rm mas. We estimate that ∼ 10 hr integrations with JWST at ∼ 1--3 μ\rm m may uncover several magnified stars whose image doublets will reveal the subhalo-induced structures of the critical curve. This method can probe a dynamic range in the subhalo to cluster halo mass ratio m/M ∼ 10-7--10-9, thereby placing new constraints on the nature of dark matter.