The correlations between optical/UV broad lines and X-ray emission for a
  large sample of quasars
  We present Chandra observations of 2106 radio-quiet quasars in the redshift
range 1.7<z<2.7 from the Sloan Digital Sky Survey (SDSS), through data release
fourteen (DR14), that do not contain broad absorption lines (BAL) in their
rest-frame UV spectra. This sample adds over a decade worth of SDSS and Chandra
observations to our previously published sample of 139 quasars from SDSS DR5
which is still used to correlate X-ray and optical/UV emission in typical
quasars. We fit the SDSS spectra for 753 of the quasars in our sample that have
high-quality (exposure time $\gtrapprox$10 ks and off-axis observation angle
<10 arcmin) X-ray observations, and analyze their X-ray-to-optical SED
properties ($\alpha_{ox}$ and $\Delta\alpha_{ox}$) with respect to the measured
CIV and MgII emission-line rest-frame equivalent width (EW) and the CIV
emission-line blueshift. We find significant correlations (at the >99.99%
level) between $\alpha_{ox}$ and these emission-line parameters, as well as
between $\Delta\alpha_{ox}$ and CIV EW. Slight correlations are found between
$\Delta\alpha_{ox}$ and CIV blueshift, MgII EW, and the CIV EW to MgII EW
ratio. The best-fit trend in each parameter space is used to compare the X-ray
weakness ($\Delta\alpha_{ox}$) and optical/UV emission properties of typical
quasars and weak-line quasars (WLQs). The WLQs typically exhibit weaker X-ray
emission than predicted by the typical quasar relationships. The best-fit
relationships for our typical quasars are consistent with predictions from the
disk-wind quasar model. The behavior of the WLQs compared to our typical
quasars can be explained by an X-ray "shielding" model.
