Detections of the 2175 A Dust Feature at 1.4 ≲ z ≲ 1.5 from the Sloan Digital Sky Survey

The strongest spectroscopic dust extinction feature in the Milky Way, thebroad absorption bump at 2175 \AA, is generally believed to be caused byaromatic carbonaceous materials -- very likely a mixture of Polycyclic AromaticHydrocarbon (PAH) molecules, the most abundant and widespread organic moleculesin the Milky Way galaxy. In this paper we report identifications of thisabsorption feature in three galaxies at $1.4 \lesssim z \lesssim 1.5$ whichproduce intervening MgII absorption toward quasars discovered by the SloanDigital Sky Survey (SDSS). The observed spectra can be fit using Galactic-typeextinction laws, characterized by parameters [R_V, E(B-V)] ~ [0.7, 0.14], [1.9,0.13], and [5.5, 0.23], respectively, where R_V=A_V/E(B-V) is thetotal-to-selective extinction ratio, E(B-V) = A_B-A_V is the color-excess.These discoveries imply that the dust in these distant quasar absorptionsystems is similar in composition to that of Milky Way, but with a range ofdifferent grain size distributions. The presence of complex aromatichydrocarbon molecules in such distant galaxies is important for bothastrophysical and astrobiological investigations.Comment: 20 pages, 4 figures, accepted for publication in ApJ July 10 issu