This article concerns the formation and structure of dark matter halos, including (1) their radial density profiles, (2) their abundance , and (3) their merger rates. The last topic may be relevant to the nature of the small, bright, high-redshift galaxies discovered by the Lyman break technique. (1) Study of a statistical sample of galaxy-mass dark halos in high-resolution Adaptive Refinement ...

The detection of stars in the process of being tidally removed from globular clusters and dwarf spheroidals in the Galaxy’s halo provides a strong constraint on their mass to light ratios and on the extent of their possible dark matter halos. If a significant dark matter component existed either within or beyond the observed stellar distribution, then stars would not be removed. We use numerica...

Extended 21cm absorption regions (dubbed “21cm absorption halos”) around first galaxies at z ∼ 30 are likely the first distinctive structures accessible to radio observations. Though the radio array capable of detecting and resolving them must have ∼ 200 km total collecting area, given the great impact of such detections to the understanding of the reionization process and cosmology, such radio...

The standard cold dark matter (CDM) model has recently been challenged by the claim that dwarf galaxies have dark matter halos with constant density cores, whereas CDM predicts halos with steeply cusped density distributions. Consequently, numerous alternative dark matter candidates have recently been proposed. In this paper, we scrutinize the observational evidence for the incongruity between ...

The distribution of image separations in multiply-imaged gravitational lens systems can simultaneously constrain the core structure of dark matter halos and cosmological parameters. We study lens statistics in flat, low-density universes with different equations of state w = pQ/ρQ for the dark energy component. The fact that dark energy modifies the distance-redshift relation and the mass funct...

We investigate the hypothesis that Lyα absorption lines arise in two populations of halos — minihalos of small circular velocity (Vc < ∼ 55 km s−1) in which star formation and metal production are inhibited by photoionization of the UV background radiation, and large galactic halos (55 < ∼ Vc < ∼ 250 km s−1) which possess stars and metals. Based on the model of Lyα-absorbing gas confined in bot...

Motivated by the recent direct detection of cosmological gas infall, we develop an analytical model for calculating the mean density profile around an initial overdensity that later forms a dark matter halo. We account for the problem of peaks within peaks; when considering a halo of a given mass we ensure that this halo is not a part of a larger virialized halo. For halos that represent high-s...

We study the properties of hot gaseous halos in 10 nearby ultraluminous IRAS galaxies observed with the ACIS instrument on board Chandra. For all sample galaxies, diffuse soft X-ray emissions are found within ∼ 10 kpc of the central region; their spectra are well fitted by a MEKAL model plus emission lines from α-elements and other ions. The temperature of the hot gas is about 0.7 keV and metal...