Turbocharging constraints on dark matter substructure through a synthesis of strong lensing flux ratios and extended lensed arcs
arxiv(2024)
Abstract
Strong gravitational lensing provides a purely gravitational means to infer
properties of dark matter halos and thereby constrain the particle nature of
dark matter. Strong lenses sometimes appear as four lensed images of a
background quasar accompanied by spatially-resolved emission from the quasar
host galaxy encircling the main deflector (lensed arcs). We present methodology
to simultaneously reconstruct lensed arcs and relative image magnifications
(flux ratios) in the presence of full populations of dark matter subhalos and
line-of-sight halos. To this end, we develop a new approach for multi-plane ray
tracing that accelerates lens mass and source light reconstruction by factors
of ∼ 100-1000. Using simulated data with a cold dark matter (CDM) ground
truth, we show that simultaneous reconstruction of lensed arcs and flux ratios
isolates small-scale perturbations to flux ratios by dark matter substructure
from uncertainties associated with the main deflector mass profile on larger
angular scales. Relative to analyses that use only image positions and flux
ratios to constrain the lens model, incorporating arcs strengthens likelihood
ratios penalizing warm dark matter (WDM) with a characteristic suppression
scale m_hm / M_⊙ in the range [10^7 - 10^7.5],
[10^7.5 - 10^8], [10^8 - 10^8.5],
[10^8.5 - 10^9] by factors of 1.3, 2.5, 5.6, and 13.1,
respectively, and the 95% exclusion limit improves by 0.5 dex in log_10
m_hm. The enhanced sensitivity to low-mass halos enabled by these
methods pushes the observational frontier of substructure lensing to the
threshold of galaxy formation, enabling stringent tests of any theory that
alters the properties of dark matter halos.
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