Quasar Microlensing at High Magnification and the Role of Dark Matter: Enhanced Fluctuations and Suppressed Saddle Points

By P. Schechter, J. Wambsganss. 2002

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Contrary to naive expectation, diluting the stellar component of the lensing galaxy in a highly magnified system with smoothly distributed "dark" matter increases rather than decreases the microlensing fluctuations caused by the remaining stars. For a bright pair of images straddling a critical curve, the saddle point (of the arrival time surface) is much more strongly affected than the associated minimum. With a mass ratio of smooth matter to microlensing matter of 4 : 1, a saddle point with a macromagnification of μ = 9.5 will spend half of its time more than a magnitude fainter than predicted. The anomalous flux ratio observed for the close pair of images in MG 0414+0534 is a factor of 5 more likely than computed by Witt, Mao, & Schechter, if the smooth matter fraction is as high as 93%. The magnification probability histograms for macroimages exhibit a distinctly different structure that varies with the smooth matter content, providing a handle on the smooth matter fraction. Enhanced fluctuations can manifest themselves either in the temporal variations of a light curve or as flux ratio anomalies in a single epoch snapshot of a multiply imaged system. While the millilensing simulations of Metcalf & Madau also give larger anomalies for saddle points than for minima, the effect appears to be less dramatic for extended subhalos than for point masses. Moreover, microlensing is distinguishable from millilensing because it will produce noticeable changes in the magnification on a timescale of a decade or less.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/cc746f3f8816ba81c005be3743a31bbe73cb9e08

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Citations in the corpus

Quantitative Interpretation of Quasar Microlensing Light Curves (2003, methodology): “…for Q2237+0305 using microlensing data, indicates that we should also be able to estimate the stellar surface density fractions in other lenses where we expect dark matter to dominate the surface density with κ∗/κ ∼ 0.1 to 0.2 (see Schechter & Wambsganss 2002, Rusin, Kochanek & Keeton 2003).”
Tests for Substructure in Gravitational Lenses (2003, background): “Most importantly, the magnification perturbations created by low optical depth substructure have a very strong dependence on the image parity, because the perturbations to the fluxes of the saddle points are skewed in the direction of demagnification (Schechter & Wambsganss 2002; Keeton 2003).”
SIZES AND TEMPERATURE PROFILES OF QUASAR ACCRETION DISKS FROM CHROMATIC MICROLENSING (2010, background): “The amplitude of microlensing perturbations decreases for very small stellar fractions, and also decreases, perhaps counterintuitively, for large stellar fractions (Schechter & Wambsganss 2002).”
Gravitational lensing (2010, background): “From a somewhat different perspective, in [418] it was discussed that decomposing lensing galaxies into microlenses has the most prominent effect when part of the lensing mass remains smooth.”
The Time Delays of Gravitational Lens HE 0435–1223: An Early-Type Galaxy with a Rising Rotation Curve (2005, background): “This provides evidence that the stars represent no more than about 20% of the total surface density of the lens galaxies at the positions of the quasar images (Schechter & Wambsganss 2002; Kochanek & Dalal 2004).”
THE SIZES OF THE X-RAY AND OPTICAL EMISSION REGIONS OF RXJ 1131–1231 (2009, background): “Note, however, that we are not in the “lagoon and caldera” regime for the microlensing patterns noted by Schechter & Wambsganss (2002) because of the very high magnifications (µ ∼ 50 for image A at lowκ∗/κ rather thanµ ∼ 10).”