Differential X-ray Absorption and Dust-To-Gas Ratios of the Lens   Galaxies SBS0909+523, FBQS0951+2635, and B1152+199
  We analyzed Chandra observations of three gravitational lenses, SBS0909+523, FBQS0951+2635, and B1152+199, to measure the differential X-ray absorption and the dust-to-gas ratio of the lens galaxies. We successfully detected the differential X-ray absorption in SBS0909+523 and B1152+199, and failed to detect it in FBQS0951+2635 due to the dramatic drop in its flux from the ROSAT epoch. These measurements significantly increase the sample of dust-to-gas ratio measurements in cosmologically-distant, normal galaxies. Using the larger sample, we obtain an average dust-to-gas ratio of E(B-V)/NH = (1.5\pm0.5)e-22 mag cm^2/atoms with an estimated intrinsic dispersion in the ratio of \simeq 40%. This average dust-to-gas ratio is consistent with our previous measurement, and the average Galactic value of 1.7e-22 mag cm^2/atoms and the estimated intrinsic dispersion is also consistent with the 30% observed in the Galaxy. A larger sample size is still needed to improve the measurements and to begin studying the evolution in the ratio with cosmic time. We also detected X-ray microlensing in SBS0909+523 and significant X-ray variability in FBQS0951+2635. 
Xinyu Dai and Christopher S. Kochanek (Ohio State University)