The dark matter haloes of dwarf galaxies: a challenge for the Λ cold dark matter paradigm?

Abstract

The cold dark matter halo mass function is much steeper than the galaxy stellar mass function on galactic and subgalactic scales. This difference is usually reconciled by assuming that the galaxy formation efficiency drops sharply with decreasing halo mass, so that virtually no dwarf galaxies form in haloes less massive than ∼10 10 M . In turn, this implies that, at any given radius, the dark mass enclosed by a galaxy must exceed a certain minimum. We use rotation curves of dwarf galaxies compiled from the literature to explore whether their enclosed mass is consistent with these constraints. We find that almost one-half of the dwarfs in our sample with stellar mass in the range of 10 6 < M gal /M < 10 7 are at odds with this restriction: either they live in haloes with masses substantially below 10 10 M or there is a mechanism capable of reducing the dark mass enclosed by some of the faintest dwarfs. Neither possibility is easily accommodated within the standard cold dark matter scenario. Extending galaxy formation to haloes well below 10 10 M would lead to large numbers of dwarf galaxies in excess of current estimates; at the same time, the extremely low stellar mass of the systems involved makes it unlikely that baryonic effects can reduce their dark matter content. Resolving this challenge seems to require new insights into dwarf galaxy formation, or perhaps a radical revision of the prevailing paradigm.

The VIMOS Ultra Deep Survey

“…A similar higher-than-expected stellar mass to halo mass ratio is observed for dwarf galaxies (e.g., Boylan-Kolchin et al 2012;Ferrero et al 2012;Miller et al 2014;Brook et al 2014;Read et al 2017). While the low-mass galaxy sub-samples used in this paper are not as low mass as the dwarf galaxies observed in the local group (the minimum stellar mass of VUDS galaxies used in our sample is M = 10 8.75 M while the masses of local dwarf galaxies are 10 6 − 10 9 M ), the low mass observationmodels discrepancy of SHMR we observe is consistent with these low-mass low redshift samples and it is possible that similar processes are behind it at high z for the higher mass galaxies.…”

The imprint of reionization on the star formation histories of dwarf galaxies

“…4 is indeed a signature of cosmic reionization. This tension between models and observation is not new, and a number of recent papers have presented compelling evidence that the halo mass of dwarf galaxies is much lower than expected from abundancematching (see, e.g., Boylan-Kolchin et al 2011;Parry et al 2012;Ferrero et al 2012). There is still no consensus on how to resolve this discrepancy, with some authors arguing that it might require a major revision to the ΛCDM paradigm (see, e.g., Bode et al 2001;Vogelsberger et al 2012) and others that it merely reflects the limitations of abundance-matching techniques when applied to the dwarf galaxy regime (Sawala et al 2014).…”

Cold dark matter: Controversies on small scales

“…Dwarfs that are far separated from a giant galaxy must rely on their own (modest) supernova reservoirs for energy injection. Ferrero et al (55) have studied a population of ∼ 10 6 − 10 7 M ⊙ field galaxies and argue that the central density problem persists even for relatively isolated dwarfs of this size. If this result holds up in further investigations, it will become a particularly serious challenge to CDM.…”