With the increasing numbers of large stellar survey projects , the quality and quantity of excellent tracers to study the Milky Way is rapidly growing , one of which is the classical Cepheids .
Classical Cepheids are high precision standard candles with very low typical uncertainties ( < 3 % ) available via the mid-infrared period-luminosity relation .
About 3500 classical Cepheids identified from OGLE , ASAS-SN , Gaia , WISE and ZTF survey data have been analyzed in this work , and their spatial distributions show a clear signature of Galactic warp .
Two kinematical methods are adopted to measure the Galactic rotation curve in the Galactocentric distance range of 4 \lesssim R _ { GC } \lesssim 19 kpc .
Gently declining rotation curves are derived by both the proper motion ( PM ) method and 3-dimensional velocity vector ( 3DV ) method .
The largest sample of classical Cepheids with most accurate 6D phase-space coordinates available to date are modeled in the 3DV method , and the resulting rotation curve is found to decline at the relatively smaller gradient of ( -1.33 \pm 0.1 ) { km s ^ { -1 } kpc ^ { -1 } } .
Comparing to results from the PM method , a higher rotation velocity ( ( 232.5 \pm 0.83 ) { km s ^ { -1 } } ) is derived at the position of Sun in the 3DV method .
The virial mass and local dark matter density are estimated from the 3DV method which is the more reliable method , M _ { vir } = ( 0.822 \pm 0.052 ) \times 10 ^ { 12 } M _ { \odot } and \rho _ { DM, \odot } = 0.33 \pm 0.03 GeV Units of GeV { cm ^ { -3 } } may be more seen in the particale physics ; For astronomers , there is a useful conversion : 0.008 M _ { \odot } { pc ^ { -3 } } = 0.3 GeV { cm ^ { -3 } } . { cm ^ { -3 } } , respectively .