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-fit 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-fit model yielded by a Markov Chain Monte Carlo analysis has thin and thick disk 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 disk density ratio of f _ { 2 } = 11 per cent , and a local density ratio of the oblate halo to the thin disk 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° < l < 240° and -1 5° < b < - 5° , 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 .