The 2Mass Redshift Survey

Abstract

With the current convergence of determinations of the Hubble Constant (e.g. The Extragalactic Distance Scale, 1997, Livio, Donahue and Panagia, eds.) to values within ±25% rather than a factor of two, and the clear possibility of determining q0 using high redshift supernovae (Garnavich et al. 1998), the major remaining problem in observational cosmology is the determination of Ω — what is the dark matter, how much is there, and how is it distributed? The most direct approach to the last two parts of the question has been to study galaxy dynamics, first through the motions of galaxies in binaries, groups and clusters, and in the last decade and a half, driven by the observation of our motion w.r.t. the Cosmic Microwave Background (CMB) and thenotion that DM must be clumped on larger scales than galaxy clusters if (Ω is to be unity, through the study of large scale galaxy flows. The ratio of the mass density to the closure mass density, Ω, is thought by most observers to be ~0.1-0.3, primarily based on the results of dynamical measurements of galaxy clusters and, more recently, gravitational lensing studies of clusters. In contrast, most theoretical cosmologists opt for a high density universe, Ω = 1.0, based on the precepts of the inflation scenario, the difficulty of forming galaxies in low density models given the observed smoothness of the microwave background radiation, and the observational evidence from the matching of the available large scale flow measurements (and the absolute microwave background dipole velocity) to the local density field. However this last result is extremely controversial—matching the velocity field to the density field derived from IRAS (60μ) selected galaxy samples yields high Ω values (e.g., Dekel et al. 1993) but matching to optically selected samples yields low values (Hudson 1994; Lahav et al. 1994; Santiago et al. 1995). On small scales, the high Ω camp argues that the true matter distribution is much more extended than the distribution of galaxies, so the dynamical mass estimates are biased low.

Dark Matter

“…Huchra initiated a near-infrared survey of nearby galaxies, the Two Micron All-Sky Survey (2MASS) (Huchra, 2000;Skrutskie et al, 2006). Photometry in 3 near-infrared spectral bands is completed, it includes about half a million galaxies up to the limiting K magnitude 13.5.…”

Global anisotropy of arrival directions of ultra-high-energy cosmic rays: capabilities of space-based detectors

“…Most of the previous studies [1] used the PSCz catalog [26] to reconstruct the source density. However, due to the limited angular resolution of the IRAS instrument used to compile the catalog it might not resolve all galaxies in the regions of high density (clusters) [27] and thus may systematically diminish the expected anisotropy due to underestimation of high number densities of galaxies. For now, the most complete full-sky catalog of galaxies is the 2MASS XSC [28].…”

“…Global anisotropy of cosmic rays with space-based detectors When the XSCz catalog [46] (see also [27]) containing distances to many 2MASS galaxies becomes available, the use of the separate database for nearby galaxies will be not necessary, and it will be possible to include the region 5 • ≤ |b| < 15 • in the study.…”

Note on galaxy catalogues in UHECR flux modelling

“…Cuoco et al 2006;Kashti & Waxman 2008;Takami et al 2009;Kashti 2009) have used the PSCz catalogue (Saunders et al 2000) for this purpose. This catalogue, however, has its drawbacks: it suffers from incomplete sky coverage, it may underestimate galaxy counts in high-density regions (Huchra et al 2007), and it has limited statistics. The 2MASS galaxy catalogue (Jarrett et al 2000;Skrutskie, M. F. et al 2006), offering complete sky coverage (except for the galactic plane) and excellent statistics, improves on these issues.…”