Small-scale double quasars discovered in the DECam Legacy Survey
  Dual quasars are precursors of binary supermassive black holes, which are
important objects for gravitational wave study, galaxy evolution, and
cosmology. I report four double quasars, one of which is newly discovered, with
separations of 1$-$2 arcsec selected from the DECam Legacy Survey. The Gemini
optical spectra confirm that both sources are quasars at the same redshifts.
J0118$-$0104 and J0932+0722 are classified as dual quasars, whereas J0037+2058
could be either a dual quasar or a lensed quasar. I estimate the physical
properties such as black hole masses and Eddington ratios for the four double
quasars. The newly discovered system supplements the incomplete sample of dual
quasars at $\sim$10 kpc at $z>0.5$. The results demonstrate that new
high-quality imaging surveys with existing spectroscopic data could reveal
additional small-scale double quasars. Combined with the dual quasars from the
literature, I find a power-law index of 1.45$\pm$0.48 for the distribution of
dual quasars as a function of separation between 5$-$20 kpc, steeper than that
expected from dynamical friction, though it is likely due to the incomplete
sample at $<$15 kpc. I also discuss the implications for future searches with
new imaging surveys such as the Dark Energy Survey and the Legacy Survey of
Space and Time.
