4.7 Article

Too big to fail in the Local Group

Journal

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 444, Issue 1, Pages 222-236

Publisher

OXFORD UNIV PRESS
DOI: 10.1093/mnras/stu1477

Keywords

galaxies: haloes; Local Group; cosmology: theory; dark matter

Funding

  1. NASA through a Hubble Space Telescope theory grant from the Space Telescope Science Institute (STScI) [AR-12836]
  2. NASA [NAS5-26555]
  3. matching equipment grant from UC-HiPACC, a multi-campus research programme - University of California Office of Research
  4. Division Of Astronomical Sciences
  5. Direct For Mathematical & Physical Scien [1009973] Funding Source: National Science Foundation

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We compare the dynamical masses of dwarf galaxies in the Local Group (LG) to those of haloes in the ELVIS (Exploring the Local Volume in Simulations) suite of Lambda cold dark matter simulations. We enumerate unaccounted-for, dense haloes (V-max greater than or similar to 25 km s(-1)) that became massive enough to have formed stars in the presence of an ionizing background (V-peak > 30 km s(-1)). Within 300 kpc of the Milky Way, the number of these objects ranges from 2 to 25 over our full sample. Moreover, this 'too big to fail' count grows when extended to the outer regions of the LG: there are 12-40 unaccounted-for massive haloes in the outskirts of the LG, a region that should be largely unaffected by any environmental processes. According to models that reproduce the LG stellar mass function, all of these missing massive systems should have M-star > 10(6) M-circle dot. We find, unexpectedly, that there is no obvious trend in the M-star-V-max relation for LG field galaxies with stellar masses in the range of similar to 10(5) - 10(8) M-circle dot. Solutions to the too big to fail problem that rely on ram pressure stripping, tidal effects, or statistical flukes appear less likely in the face of these results.

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