skip to main content

This content will become publicly available on November 9, 2017

Title: A common origin for globular clusters and ultra-faint dwarfs in simulations of the first galaxies

In this study, the first in a series on galaxy formation before reionization, we focus on understanding what determines the size and morphology of stellar objects in the first low-mass galaxies, using parsec-scale cosmological simulations performed with an adaptive mesh hydrodynamics code. Although the dense gas in which stars are formed tends to have a disk structure, stars are found in spheroids with little rotation. Halos with masses between $${10}^{6}\,{M}_{\odot }$$ and $$5\times {10}^{8}\,{M}_{\odot }$$ form stars stochastically, with stellar masses in the range $${10}^{4}\,{M}_{\odot }$$ to $$2\times {10}^{6}\,{M}_{\odot }$$. We observe, nearly independent of stellar mass, a large range of half-light radii for the stars, from a few parsecs to a few hundred parsecs and surface brightnesses and mass-to-light ratios ranging from those typical of globular clusters to ultra-faint dwarfs. In our simulations, stars form in dense stellar clusters with high gas-to-star conversion efficiencies and rather uniform metallicities. A fraction of these clusters remain bound after the gas is removed by feedback, but others are destroyed, and their stars, which typically have velocity dispersions of 20–40 km s–1, expand until they become bound by the dark matter halo. We thus speculate that the stars in ultra-faint dwarf galaxies may show kinematic and chemical signatures consistent with their origin in a few distinct stellar clusters. On the other hand, some globular clusters may form at the center of primordial dwarf galaxies and may contain dark matter, perhaps detectable in the outer parts.
Authors:
ORCiD logo [1] ;  [1] ;  [2]
  1. Univ. of Maryland, College Park, MD (United States)
  2. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); The Univ. of Chicago, Chicago, IL (United States)
Publication Date:
OSTI Identifier:
1331773
Report Number(s):
FERMILAB-PUB-16-286-A; arXiv:1607.04291
Journal ID: ISSN 1538-4357; 1476324
Grant/Contract Number:
AC02-07CH11359
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 831; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; theory; galaxies: evolution; galaxies: formation; methods: numerical