Apparent Clustering of Intermediate-Redshift Galaxies as a Probe of Dark Energy

Abstract

We show the apparent redshift-space clustering of galaxies in redshift range of 0.2-0.4 provides surprisingly useful constraints on dark energy component in the universe, because of the right balance between the density of objects and the survey depth. We apply Fisher matrix analysis to the the Luminous Red Galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS), as a concrete example. Possible degeneracies in the evolution of the equation of state (EOS) and the other cosmological parameters are clarified.PACS numbers: 98.80. Es, 95.35.+d, 98.62.Py The dark energy, such as the cosmological constant, has now turned out to be a necessary element to understand our universe. There are many indirect suggestions for the dark energy, including the age of the universe, the formation of the large-scale structure, the number count of the galaxies, and so on [1]. More striking evidences stem from the combination of acoustic peaks of temperature fluctuations in cosmic microwave background radiation (CMB) [2] and the Hubble diagram of the type Ia supernova [3]. Natural expectation for the dark energy is arisen from the vacuum fluctuations of quantum fields, although the smallness of its observed value is extremely unnatural [4].Since the energy density of the cosmological constant is constant in time by definition, one needs an extremely suspicious fine-tuning of 120 digits to set a correct value at an initial stage (probably Planck time) so that the energy density of the cosmological constant should be comparable with the matter density today. Alternatively, such stringent fine-tuning should be moderated if the dark energy component consists of some dynamical field such as "quintessence" [5,6]. In general, such dynamical dark energy affects cosmological observations through a time-dependent EOS, which is characterized by a parameter w(t) = p/ρ. If w is found to be different from −1, the dark energy is proven to be different from the simple cosmological constant. Current observational data are consistent with the cosmological constant [7,8], although they are still not enough to impose sufficient constraints on the EOS.Since the dark energy has profound implications on the nature of the universe, it is of great importance to explore the origin of dark energy. Near-future observations will enable us to clarify whether the dark energy is a mere cosmological constant or something else. Cosmological observations, such as the Type Ia supernovae [9], CMB fluctuations [6,8,10], cluster mass function [11], weak lensing field [12], and so on, are useful tools to probe the nature of the dark energy.It is shown [13] that an application of the AlcockPaczynski (AP) test [14] to the redshift-space correlation function of the high-redshift objects can be a useful probe of the cosmological constant. In literatures, this method is mainly applied to the Lyman-α forest [15], the Lyman-break galaxies [16], and the quasars [17], etc.A drawback of the high-redshift objects is their sparseness. Relatively high shot noise prevents to accurately d...

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