Galaxies dark matter halo

Reconciliation (or perhaps clearer contradictions ) of the details of structures made by x-CDM simulations with those in the real world. The standard problems are generally described as missing satellites (the expectation of more substructure in dark matter halos than we see in the luminous stuff) and core/cusp (the steeper rise in central density of the simulations than we see in centers of galaxies and clusters). There are perhaps some other issues, like the pair-wise velocity dispersion. All occur on length scales where feedback from what the baryons are doing must be important and has not yet been fully included in the calculations. 

A. Burkert (1995). The structure of dark matter halos in dwarf galaxies , Astrophysical Journal, v.447, pp.25-28. 

Galaxies always occur as clusters like shown in Fig. 7.13. The luminous galaxies we see sit within larger, more massive dark matter halos. This can be deduced from... 

We present preliminary results on the intrinsic shapes of s[nral galaxy disks, based on a K -band imaging surrey. The sample galaxies were selected to be face-on on the basis of their HI linewidths and their luminosities. We fit two-dimensional bulge-disk modds that minimize the impact of spiral structure on the apparent shape. We find that for the majority of galaxies the intrinsic disk ellipticity at a few scale lengths is 0.35 and briefly discuss implications for the diape of the dark matter halos and for the intrinsic scatter in the TuUy-Fisher relation. 

The existence of dark matter (either baryonic or non-baryonic) is inferred from its gravitational effects on galactic rotation curves, the velocity dispersions and hydrostatic equilibrium of hot (X-ray) gas in clusters and groups of galaxies, gravitational lensing and departures from the smooth Hubble flow described by Eq. (4.1). This dark matter resides at least partly in the halos of galaxies such as our... 

Fig. A 1.1. Orbital speed as a function of distance from the centre of the galaxy NGC 3198. The flat part of the curve can only be explained under the assumption that there is a massive halo of dark matter. Points correspond to observations. Curves show contributions from the disk and the halo, calculated using a suitable model.

It is thus assumed that the (rotational) speeding offences committed in the galactic periphery are due to the existence of a massive halo of invisible matter. In our own Galaxy, there must be ten times as much dark matter as visible matter, amounting to some 1000 biUion solar masses. We may deduce that the same is true of aU... 

Gravitahonal (micro) lensing is now recognised as a way of revealing otherwise hidden matter. It is universally used to estimate the distribution and quantity of dark matter on a variety of distance scales. The study of dark matter in the halo of our own Galaxy is not the least significant amongst these. 

First, it is useful to know that a model spiral galaxy can be considered to consist of a central spherical bulge component, embedded in a rotating disk of stellar and gaseous material with the whole embedded in a spherical halo of very diffuse gas and halo stars. It is conventionally believed that this latter component is much more massive than it appears, with the deficit made up of dark matter. ... 

Neutrinos can be cold dark matter if their masses are around few GeV or a TeV. However, fourth-generation heavy neutrinos lighter than 45 GeV are excluded by the measurement of the Z-boson decay width at the Large Electron-Positron collider at CERN. Moreover, direct searches for WIMP dark matter in our galaxy exclude Dirac neutrinos heavier than 0.5 GeV as the dominant component of the galactic dark halo (see Figure 3). Thus although heavy Dirac neutrinos could still be a tiny part of the halo dark matter, they cannot solve the cold dark matter problem. 

The idea here is that neutralino dark matter is to be found not only in the halo of our galaxy and in our solar system, but also here on Earth and in the room we are in. Thus if we could set up a detector that records the passage of dark matter neutralinos, we could hope of detecting neutralino dark matter. 

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