We analyzed Chandra observations of three gravitational lenses , SBS 0909+523 , FBQS 0951+2635 , and B 1152+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 SBS 0909+523 and B 1152+199 , and failed to detect it in FBQS 0951+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 ) / { N } _ { H } = ( 1.5 \pm 0.5 ) \times 10 ^ { -22 } mag cm ^ { 2 } atoms ^ { -1 } 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 1.7 \times 10 ^ { -22 } mag cm ^ { 2 } atoms ^ { -1 } 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 SBS 0909+523 and significant X-ray variability in FBQS 0951+2635 .