Where Is the Dark Matter?

Abstract

How much dark matter is there in the universe and where is it located? These are two of the most fundamental questions in cosmology. We use in this paper optical and X-ray mass determinations of galaxies, groups, and clusters of galaxies to suggest that most of the dark matter may reside in very large halos around galaxies, typically extending to 1200 kpc for bright galaxies. We show that the mass-to-light ratio of galaxy systems does not increase significantly with linear scale beyond the very large halos suggested for individual galaxies. Rather, the total mass of large-scale systems such as groups and rich clusters of galaxies, even superclusters, can on average be accounted for by the total mass of their member galaxies, including their large halos (which may be stripped off in the dense cluster environment but still remain in the clusters) plus the mass of the hot intracluster gas. This conclusion also suggests that we may live in a low-density universe with ⍀ 1 0.2-0.3.

A comparison of different cluster mass estimates: consistency or discrepancy?

“…As a result, we have to accept a low mass density universe of Ωm ≈ 0.1-0.4, as suggested by the two independent measurements of the cluster matter compositions, the ratio M/L [(dark+luminous)/luminous] (e.g. Bahcall, Lubin, & Dorman, 1995) and the baryon fraction f b [baryon/(baryon+nonbaryon)] (e.g. White et al 1993).…”

“…In particular, their matter composition, the mass-to-light ratio M/L (e.g. Bahcall, Lubin, & Dorman 1995) and the baryon fraction f b (e.g. White et al, 1993) play a potentially important role in the direct measurement of mean mass density of the universe, Ωm.…”

“…It appears that the observational and theoretical results are likely to merge nowadays, in favor of a low mass density universe of Ωm ∼ 0.3 (e.g. Bahcall et al 1995;Ostriker & Steinhardt 1995). Yet, the key issue in such a "direct" measurement of the cosmological density parameter is closely connected to the question of how accurately one can determine the total gravitating masses of galaxy clusters.…”

A Review on the Scalar Field/Bose-Einstein Condensate Dark Matter Model

“…This widely accepted monotonic increase of M/L with scale determines to a large extent the prevalent views about the location of the dark matter and the total mass density of the Universe. Recent studies of the dependence of the mass-to-light ratio on scale indicate that M/L is nearly constant on large scales ranging up to supercluster size (10Mpc), suggesting no additional dark matter is tucked away on large scales [10]. More recently, a clear separation between the center of baryonic matter and the total center of mass was observed in the Bullet cluster ( [27]) and later in other galaxy cluster collisions ( [20]).…”

Cluster detection from surface-brightness fluctuations in SDSS data

“…Bahcall et al 1995;Carlberg et al 1996;Carlberg et al 1997a;Gonzalez et al 2000), however with a scatter of ∼20%. We normalise the combined cluster spectrum such that the B-band mass-to-light ratio at redshift zero is 250 in solar units.…”