Identifying RR Lyrae Variable Stars in Six Years of the Dark Energy Survey

We present a search for RR Lyrae stars using the full six-year data set from Dark Energy Survey (DES) covering ~5,000 sq. deg. of southern sky. Using multi-stage multi-variate classification and light curve template-fitting scheme, we identify candidates with median 35 observations per candidate. detect 6,971 out to ~335 kpc, estimate that our sample is >70% complete at ~150 kpc. find excellent agreement other wide-area catalogs studies targeting Magellanic Clouds Milky Way satellite galaxies. fit smooth stellar halo density profile broken-power-law model fixed flattening (q = 0.7), strong evidence break $R_0 32.1^{+1.1}_{-0.9}$ kpc an inner slope $n_1 -2.54^{+0.09}_{-0.09}$ outer $n_2 -5.42^{+0.13}_{-0.14}$. use catalog perform galaxies large sizes low luminosities. simulated galaxies, Lyrae-based more sensitive than those resolved populations in regime ($r_h > 500$ pc), low-surface-brightness dwarf A blind large, diffuse satellites yields three candidate substructures. The first can be confidently associated galaxy Eridanus II. second has similar distance proper motion ultra-faint Tucana II but separated by ~5 third close projection globular cluster NGC 1851 ~10 distant appears differ motion.