  We analyze the near-infrared to UV data of 16 quasars with redshifts ranging
from 0.71 $<$ $z$ $<$ 2.13 to investigate dust extinction properties. The
sample presented in this work is obtained from the High $A_V$ Quasar (HAQ)
survey. The quasar candidates were selected from the Sloan Digital Sky Survey
(SDSS) and the UKIRT Infrared Deep Sky Survey (UKIDSS), and follow-up
spectroscopy was carried out at the Nordic Optical Telescope (NOT) and the New
Technology Telescope (NTT). To study dust extinction curves intrinsic to the
quasars, from the HAQ survey we selected 16 cases where the Small Magellanic
Cloud (SMC) law could not provide a good solution to the spectral energy
distributions (SEDs). We derived the extinction curves using Fitzpatrick &
Massa 1986 (FM) law by comparing the observed SEDs to the combined quasar
template from Vanden Berk et al. 2001 and Glikman et al. 2006. The derived
extinction, $A_V$, ranges from 0.2-1.0 mag. All the individual extinction
curves of our quasars are steeper ($R_V=2.2$-2.7) than that of the SMC, with a
weighted mean value of $R_V=2.4$. We derive an `average quasar extinction
curve' for our sample by fitting SEDs simultaneously by using the weighted mean
values of the FM law parameters and a varying $R_V$. The entire sample is well
fit with a single best-fit value of $R_V=2.2\pm0.2$. The `average quasar
extinction curve' deviates from the steepest Milky Way and SMC extinction
curves at a confidence level $\gtrsim95\%$. Such steep extinction curves
suggest a significant population of silicates to produce small dust grains.
Moreover, another possibility could be that the large dust grains may have been
destroyed by the activity of the nearby active galactic nuclei (AGN), resulting
in steep extinction curves.

Astrophysics of Galaxies;Cosmology and Nongalactic Astrophysics