The observed mass profiles of dark halos and the formation epoch of galaxies

Shinji Sato, Fumie Akimoto, Akihiro Furuzawa, Yuzuru Tawara, Manabu Watanabe, Yasuki Kumai

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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 rsc relation. For M200 = 1012-1015 M, 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.

Original languageEnglish
Pages (from-to)L73-L76
JournalAstrophysical Journal
Issue number2 PART 2
Publication statusPublished - 10-07-2000


All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Sato, S., Akimoto, F., Furuzawa, A., Tawara, Y., Watanabe, M., & Kumai, Y. (2000). The observed mass profiles of dark halos and the formation epoch of galaxies. Astrophysical Journal, 537(2 PART 2), L73-L76.