Dark Matter Subhalos and the Dwarf Satellites of the Milky Way

• Published in: The Astrophysical journal Vol. 679; no. 2; pp. 1260 - 1271
• Main Authors: Madau, Piero, Diemand, Jürg, Kuhlen, Michael
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 01.06.2008; University of Chicago Press
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Galaxy halo; Dark matter; Galaxy formation; Dwarf galaxies; galaxies: dwarf ¯ galaxies: formation; Cosmology; Numerical method; Milky Way; methods: numerical; galaxies: halos; cosmology: theory
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/587545

The Via Lactea simulation of the cold dark matter halo of the Milky Way predicts the existence of many thousands of bound subhalos with masses above 10 super(6) M sub([image]), distributed approximately with equal mass per decade of mass. Here we show that (1) a similar steeply rising subhalo mass function is also present at redshift [image] in an elliptical-sized halo simulated with comparable resolution in a different cosmology. Compared to Via Lactea, this run produces nearly a factor of 2 more subhalos with large circular velocities; (2) the fraction of Via Lactea mass brought in by subhalos that have a surviving bound remnant today reaches 45%. Most of the Via Lactea mass is acquired in resolved discrete clumps, with no evidence for a significant smooth infall; (3) because of tidal mass loss, the number of subhalos surviving today that reached a peak circular velocity of >10 km s super(-1) throughout their lifetime exceeds half a thousand, 5 times larger than their present-day abundance; (4) unless the circular velocity profiles of Galactic satellites peak at values significantly higher that expected from the stellar line-of-sight velocity dispersion, only about one in five subhalos with [image] km s super(-1) today must be housing a luminous dwarf; (5) nearly 600 halos with masses greater than 10 super(7)M sub([image]) are found today in the ``field'' between r sub(200) and 1.5r sub(200), i.e. small dark matter clumps appear to be relatively inefficient at forming stars even well beyond the virial radius; 6) the observed Milky Way satellites appear to follow the overall dark matter distribution of Via Lactea, while the largest simulated subhalos today are found preferentially at larger radii; (7) subhalos have central densities that increase with [image] and reach [image] M sub([image]) pc super(-3), comparable to the central densities inferred in dwarf spheroidals with core radii >250 pc.