Dissecting the Gaseous Halos of z~2 Damped Ly$\alpha$ Systems with Close
  Quasar Pairs
  We use spectroscopy of close pairs of quasars to study diffuse gas in the
circumgalactic medium (CGM) surrounding a sample of 40 Damped Lya systems
(DLAs). The primary sightline in each quasar pair probes an intervening DLA in
the redshift range 1.6 < z_DLA < 3.6, such that the second quasar sightline
then probes Lya, CII, SiII, and CIV absorption in the CGM transverse to the DLA
to projected distances $R_{\perp} < 300$ kpc. Analysis of the Lya profiles in
these CGM sightlines constrains the covering fraction (f_C) of optically thick
HI (having column density N_HI > 10^17.2 cm^-2) to be greater than ~30% within
$R_{\perp} < 200$ kpc of DLAs. Strong SiII 1526 absorption with equivalent
width W_1526 > 0.2 Ang occurs with an incidence f_C (W_1526 > 0.2 Ang) =
20(+12/-8)% within $R_{\perp}<100$ kpc, indicating that low-ionization metal
absorption associated with DLAs probes material at a physical distance R_3D <
30 kpc. However, we find that strong CIV 1548 absorption is ubiquitous in these
environments (f_C (W_1548 > 0.2 Ang) = 57(+12/-13)% within $R_{\perp} < 100$
kpc), and in addition exhibits a high degree of kinematic coherence on scales
up to ~175 kpc. We infer that this high-ionization material arises
predominantly in large, quiescent structures extending beyond the scale of the
DLA host dark matter halos rather than in ongoing galactic winds. The Lya
equivalent width in the DLA-CGM is anticorrelated with $R_{\perp}$ at >98%
confidence, suggesting that DLAs arise close to the centers of their host halos
rather than on their outskirts. Finally, the average Lya, CII and CIV
equivalent widths are consistent with those measured around z~2 Lyman Break
Galaxies. Assuming that DLAs trace a galaxy population with lower masses and
luminosities, this finding implies that the absorption strength of cool
circumgalactic material has a weak dependence on dark matter halo mass for M_h
< 10^12 M_sun.
