The Observed Mass Profiles of Dark Halos and the Formation
Epoch of Galaxies
Sato, Shinji; Akimoto, Fumie; Furuzawa, Akihiro; Tawara, Yuzuru; Watanabe, Manabu; Kumai, Yasuki
Abstract
We have determined the mass profiles of dark halos in 83 objects
observed by ASCA. The point-spread function of the X-ray telescope was
deconvoled by the Richardson-Lucy algorithm, and the temperature
profiles were calculated to obtain the mass profiles. The derived mass
profiles are consistent with the Navarro, Frenk, & White model in
(0.01-1.0)rvirial. We found a good correlation between the
scale radius rs and the characteristic mass density
δc, which indicates the self-similarity of dark halos.
The spectrum index of primordial density fluctuation,
P(k)~kn, was determined from the slope of the
rs-δc relation. For
M200=1012-1015 Msolar, our
analysis gives n=-1.2+/-0.3 with a confidence level of 90%. The mass
density of dark halos is a good indicator of the mean mass density of
the universe at the time when the halos were assembled, z=zf.
Assuming δc~(1+zf)3, we have
determined the epoch when each dark halo was assembled. Our analysis
indicates that the field elliptical galaxies and groups of galaxies
formed approximately at 1+zf~=15 and at
1+zf~=7-10, respectively.