Constraining the Galactic structure parameters with the XSTPS-GAC and SDSS photometric surveys

Photometric data from the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC) and the Sloan Digital Sky Survey (SDSS) are used to derive the global structure parameters of the smooth components of the Milky Way. The data, which cover nearly 11 000 deg(2) sky area and the full range of Galactic latitude, allow us to construct a globally representative Galactic model. The number density distribution of Galactic halo stars is fitted with an oblate spheroid that decays by power law. The best fitting yields an axis ratio and a power-law index kappa = 0.65 and p = 2.79, respectively. The r-band differential star counts of three dwarf samples are then fitted with a Galactic model. The best-fitting model yielded by a Markov Chain Monte Carlo analysis has thin and thick disc scale heights and lengths of H-1 = 322 pc and L-1 = 2343 pc, H-2 = 794 pc and L-2 = 3638 pc, a local thick-to-thin disc density ratio of f(2) = 11 per cent, and a local density ratio of the oblate halo to the thin disc of f(h) = 0.16 per cent. The measured star count distribution, which is in good agreement with the above model for most of the sky area, shows a number of statistically significant large-scale overdensities, including some of the previously known substructures, such as the Virgo overdensity and the so-called 'north near structure', and a new feature between 150 degrees < l < 240 degrees and -1 degrees < b < -5 degrees, at an estimated distance between 1.0 and 1.5 kpc. The Galactic North-South asymmetry in the anticentre is even stronger than previously thought.National Key Basic Research Program of China [2014CB845700]; China Postdoctoral Science Foundation [2016M590014]; National Natural Science Foundation of China [11443006, U1531244]; National Development and Reform Commission; Alfred P. Sloan Foundation; National Science Foundation; U.S. Department of Energy Office of Science; University of Arizona; Brazilian Participation Group; Brookhaven National Laboratory; Carnegie Mellon University; University of Florida; French Participation Group; German Participation Group; Harvard University; Instituto de Astrofisica de Canarias; Michigan State/Notre Dame/JINA Participation Group; Johns Hopkins University; Lawrence Berkeley National Laboratory; Max Planck Institute for Astrophysics; Max Planck Institute for Extraterrestrial Physics; New Mexico State University; New York University; Ohio State University; Pennsylvania State University; University of Portsmouth; Princeton University; Spanish Participation Group; University of Tokyo; University of Utah; Vanderbilt University; University of Virginia; University of Washington; Yale UniversitySCI(E)ARTICLE32545-255646