In this paper, we look at how the appearance of dark halos that have failed to form galaxies changes the relation between galaxies and dark matter halos.
Abundance matching is a very neat method of statistically linking (simulated) dark matter halos to (observed). It requires no detailed knowledge about galaxy formation physics and just assumes that each halo contains exactly one galaxy, with brighter galaxies living in more massive halos. From these simple assumptions, one can derive average the stellar mass – halo mass relation for all galaxies.
It had been argued (including by myself) that the average relation inferred from abundance matching does not match the values measured for individual dwarf galaxies, whether by observations or direct simulations. This has been interpreted as a problem for the LCDM model, which seemed to produce too many halos. However, what we show in our new paper is that the simple assumption of one galaxy per halo breaks down for low mass halos, because many of them do not host a galaxy at all. We find that once these “dark” halos and other baryonic effects are taken into account, the stellar-halo mass relation bends upwards and matches the observations.
From Fig. 4: The classic abundance matching relation (black line) does not match the data (squares and triangles) at the low mass end. However, after the relation gets bent by baryons (red line), the disagreement is resolved.
If you’d like to read more, please take a look at our paper.
Collaborators: Carlos S. Frenk, Azadeh Fattahi, Julio F. Navarro, Richard G. Bower, Robert A. Crain, Claudio Dalla Vecchia, Michelle Furlong, Adrian Jenkins, Ian G. McCarthy, Yan Qu, Matthieu Schaller, Joop Schaye, Tom Theuns