We homogeneously analyzed the Chandra X-ray observations of 10 gravitational lenses , HE 0047 - 1756 , QJ 0158 - 4325 , SDSS 0246 - 0805 , HE 0435 - 1223 , SDSS 0924 + 0219 , SDSS 1004+4112 , HE 1104 - 1805 , PG 1115+080 , Q 1355 - 2257 , and Q 2237+0305 , to measure the differential X-ray absorption between images , the metallicity , and the dust-to-gas ratio of the lens galaxies .
We detected differential absorption in all lenses except SDSS 0924 + 0219 and HE 1104 -1805 .
This doubles the sample of dust-to-gas ratio measurements in cosmologically distant lens galaxies .
We successfully measured the gas phase metallicity of three lenses , Q 2237+0305 , SDSS 1004+4112 , and B 1152 + 199 from the X-ray spectra .
Our results suggest a linear correlation between metallicity and dust-to-gas ratio ( i.e. , a constant metal-to-dust ratio ) , consistent with what is found for nearby galaxies .
We obtain an average dust-to-gas ratio E ( B - V ) / N _ { H } = 1.17 ^ { +0.41 } _ { -0.31 } \times 10 ^ { -22 } mag cm ^ { 2 } atom ^ { -1 } in the lens galaxies , with an intrinsic scatter of 0.3 dex .
Combining these results with data from GRB afterglows and quasar foreground absorbers , we found a mean dust-to-gas ratio 0.54 ^ { +0.19 } _ { -0.14 } \times 10 ^ { -22 } mag cm ^ { 2 } atom ^ { -1 } , now significantly lower than the average Galactic value , 1.7 \times 10 ^ { -22 } mag cm ^ { 2 } atoms ^ { -1 } . This suggests evolution of dust-to-gas ratios with redshift and lower average metallicities for the higher redshift galaxies , consistent with current metal and dust evolution models of interstellar medium .
The slow evolution in the metal-to-dust ratio with redshift implies very rapid dust formation in high redshift ( z > 2 ) galaxies .