The Metal-poor Metallicity Distribution of the Ancient Milky Way

Abstract

We present a low-metallicity map of the Milky Way consisting of ∼110,000 metal-poor giants with −3.5 −2.0), we recover a clear spatial dependence of decreasing mean metallicity as a function of scale height that maps onto the thick disk component of the Milky Way. When only considering the very metal-poor stars in our sample ([Fe/H] < −2), we recover no such spatial dependence in their mean metallicity out to a scale height of ∣ Z ∣ ∼ 7 kpc. We find that the metallicity distribution function (MDF) of the most metal-poor stars in our sample (−3.0 < −2.3, the MDF is largely insensitive to scale height ∣ Z ∣ out to ∼5 kpc, showing that very and extremely metal-poor stars are in every galactic component.