Where are the Fossils of the First Galaxies? I. Local Volume Maps and Properties of the Undetected Dwarfs

Details Where are the Fossils of the First Galaxies? I. Local Volume Maps and Properties of the Undetected Dwarfs Where are the Fossils of the First Galaxies? I. Local Volume Maps and Properties of the Undetected Dwarfs

2010-10-11

arxiv.org/abs/1010.2231v2

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

published in ApJ October 2011 with minor revisions V. 741 article ID. 18

Scientific paper

We present a new method for generating initial conditions for LCDM N-body simulations which provides the dynamical range necessary to follow the evolution and distribution of the fossils of the first galaxies on Local Volume, 5-10 Mpc, scales. The initial distribution of particles represents the position, velocity and mass distribution of the dark and luminous halos extracted from pre-reionization simulations. We confirm previous results that ultra-faint dwarfs have properties compatible with being well preserved fossils of the first galaxies. However, because the brightest pre-reionization dwarfs form preferentially in biased regions, they most likely merge into non-fossil halos with circular velocities >20-30 km/s. Hence, we find that the maximum luminosity of true-fossils in the Milky Way is L_V<10^5 L_solar, casting doubts on the interpretation that some classical dSphs are true-fossils. In addition, we argue that most ultra-faints at small galactocentric distance, R<50 kpc, had their stellar properties modified by tides, while a large population of fossils is still undetected due to their extremely low surface brightness log(Sigma_V) < -1.4. We estimate that the region outside R_50 (~ 400 kpc) up to 1 Mpc from the Milky Way contains about a hundred true fossils of the first galaxies with V-band luminosities 10^3 - 10^5 L_solar and half-light radii, r_hl ~ 100-1000 pc.

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