arXiv subjects

Dragan Huterer

Publications and source records attributed to Dragan Huterer.

153 records · Page 9Linked to original sources

arXiv2001

Measuring Angular Diameter Distances through Halo Clustering

Current and upcoming wide-field surveys for weak gravitational lensing and the Sunyaev-Zel'dovich effect will generate mass-selected catalogues of dark matter halos with internal or followup photometric redshift information. The angular power spectrum of these halos provides additional information that complements the previously-studied number counts. In particular, using the shape of the linear power spectrum as a standard ruler that is calibrated by cosmic microwave background measurements, we find that a survey of 4000 sqr. deg. and a mass threshold of 10^14 M_sun can be used to determine the comoving angular diameter distance as a function of redshift. In principle, this test also allows an absolute calibration of the distance scale and measurement of the Hubble constant. This test is largely insensitive to the details of halo mass measurements, mass function, and halo bias. Determination of these quantities would further allow a measurement of the linear growth rate of fluctuations.

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arXiv2001

Constraining the Properties of Dark Energy

The presence of dark energy in the Universe is inferred directly from the accelerated expansion of the Universe, and indirectly, from measurements of cosmic microwave background (CMB) anisotropy. Dark energy contributes about 2/3 of the critical density, is very smoothly distributed, and has large negative pressure. Its nature is very much unknown. Most of its discernible consequences follow from its effect on evolution of the expansion rate of the Universe, which in turn affects the growth of density perturbations and the age of the Universe, and can be probed by the classical kinematic cosmological tests. Absent a compelling theoretical model (or even a class of models), we describe dark energy by an effective equation of state w=p_X/rho_X which is allowed to vary with time. We describe and compare different approaches for determining w(t), including magnitude-redshift (Hubble) diagram, number counts of galaxies and clusters, and CMB anisotropy, focusing particular attention on the use of a sample of several thousand type Ia supernova with redshifts z < 1.7, as might be gathered by the proposed SNAP satellite. Among other things, we derive optimal strategies for constraining cosmological parameters using type Ia supernovae. While in the near term CMB anisotropy will provide the first measurements of w, supernovae and number counts appear to have the most potential to probe dark energy.

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arXiv2001

The Angular Power Spectrum of EDSGC Galaxies

We determine the angular power spectrum, C_l, of the Edinburgh/Durham Southern Galaxy Catalog (EDSGC) and use this statistic to constrain cosmological parameters. Our methods for determining C_l, and the parameters that affect it are based on those developed for the analysis of cosmic microwave background maps. We expect them to be useful for future surveys. Assuming flat cold dark matter models with a cosmological constant (constrained by COBE/DMR and local cluster abundances), and a scale--independent bias, b, we find good fits to the EDSGC angular power spectrum with 1.11 < b < 2.35 and 0.2 < Omega_m < 0.55 at 95% confidence. These results are not significantly affected by the ``integral constraint'' or extinction by interstellar dust, but may be by our assumption of Gaussianity.

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arXiv2000

Probing the dark energy: methods and strategies

The presence of dark energy in the Universe is inferred directly from the accelerated expansion of the Universe, and indirectly, from measurements of cosmic microwave background (CMB) anisotropy. Dark energy contributes about 2/3 of the critical density, is very smoothly distributed, and has large negative pressure. Its nature is very much unknown. Most of its discernible consequences follow from its effect on evolution of the expansion rate of the Universe, which in turn affects the growth of density perturbations and the age of the Universe, and can be probed by the classical kinematic cosmological tests. Absent a compelling theoretical model (or even a class of models), we describe the dark energy by an effective equation-of-state w=p_X/ρ_X which is allowed to vary with time. We describe and compare different approaches for determining w(t), including magnitude-redshift (Hubble) diagram, number counts of galaxies and clusters, and CMB anisotropy, focusing particular attention on the use of a sample of several thousand type Ia supernova with redshifts z\lesssim 1.7, as might be gathered by the proposed SNAP satellite. Among other things, we derive optimal strategies for constraining cosmological parameters using type Ia supernovae. While in the near term CMB anisotropy will provide the first measurements of w, supernovae and number counts appear to have the most potential to probe dark energy.

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arXiv2000

Probing the Cosmic Dark Age in X-rays

Empirical studies of the first generation of stars and quasars will likely become feasible within the next decade in several different wavelength bands. Microwave anisotropy experiments, such as MAP or Planck, will set constraints on the ionization history of the intergalactic medium due to these sources. In the infrared, the Next Generation Space Telescope (NGST) will be able to directly detect sub-galactic objects at redshifts z>10. In the optical, data from the Hubble Deep Field already places a constraint on the abundance of high-redshift quasars. However, the epoch of the first quasars might be first probed in X-ray bands, by instruments such as the Chandra X-ray Observatory (CXO) and the X-ray Multi-mirror Mission (XMM). In a 500 Ksec integration, CXO reaches a sensitivity of 2x10-16 erg/s cm^2. Based on simple hierarchical CDM models, we find that at this flux threshold approx. 100 quasars might be detectable from redshifts z>5, and approx. 1 quasar at z=10, in each 17x17 arcmin field. Measurement of the power spectrum of the unresolved soft X-ray background will further constrain models of faint, high-redshift quasars.

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arXiv1999

On the degree of scale invariance of inflationary perturbations

Many, if not most, inflationary models predict the power-law index of the spectrum of density perturbations is close to one, though not precisely equal to one, |n-1| \sim O(0.1), implying that the spectrum of density perturbations is nearly, but not exactly, scale invariant. Some models allow n to be significantly less than one (n \sim 0.7); a spectral index significantly greater than one is more difficult to achieve. We show that n \approx 1 is a consequence of the slow-roll conditions for inflation and ``naturalness,'' and thus is a generic prediction of inflation. We discuss what is required to deviate significantly from scale invariance, and then show, by explicit construction, the existence of smooth potentials that satisfy all the conditions for successful inflation and give $n$ as large as 2.

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arXiv1999

Prospects for probing the dark energy via supernova distance measurements

Distance measurements to Type Ia supernovae (SNe Ia) indicate that the Universe is accelerating and that two-thirds of the critical energy density exists in a dark-energy component with negative pressure. Distance measurements to SNe Ia can be used to distinguish between different possibilities for the dark energy, and if it is an evolving scalar field, to reconstruct the scalar-field potential. We derive the reconstruction equations and address the feasibility of this approach by Monte-Carlo simulation.

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arXiv1999

Gravitational Lensing as a Probe of Quintessence

A large number of cosmological studies now suggest that roughly two-thirds of the critical energy density of the Universe exists in a component with negative pressure. If the equation of state of such an energy component varies with time, it should in principle be possible to identify such a variation using cosmological probes over a wide range in redshift. Proper detection of any time variation, however, requires cosmological probes beyond the currently studied range in redshift of $\sim$ 0.1 to 1. We extend our analysis to gravitational lensing statistics at high redshift and suggest that a reliable sample of lensed sources, out to a redshift of $\sim$ 5, can be used to constrain the variation of the equation of state, provided that both the redshift distribution of lensed sources and the selection function involved with the lensed source discovery process are known. An exciting opportunity to catalog an adequate sample of lensed sources (quasars) to probe quintessence is now available with the ongoing Sloan Digital Sky Survey. Writing $w(z)\approx w_0 + z (dw/dz)_0$, we study the expected accuracy to which the equation of state today $w_0$ and its rate of change $(dw/dz)_0$ can simultaneously be constrained. Such a determination can rule out some missing-energy candidates, such as classes of quintessence models or a cosmological constant.

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arXiv1995

Distances to Nearby Galaxies: Combining Fragmentary Data Using Four Different Methods

The primary distance indicators are established in our Galaxy and the Local Group. There are at least four different methods which give good distances: methods using proper motions, RR Lyraes, Cepheid variables, and Type II supernovae. However the data on independent distances is very fragmentary, due partly to nature and partly to technological limits. As a result the data are rarely put together in a consistent way; instead, the discussion of distance scales is often focused on one or two methods or on individual objects. Hence the question: what is the current situation with our overall knowledge of distances to the nearby galaxies? We try to answer this question by combining the fragmentary data from all four methods for fifteen objects: the galactic center, the globular clusters M2, M3, M4, M13, M22, M92, and 47 Tuc, the galaxies IC1613, M31, M33, M81, M100, and M101, and the Large Magellanic Cloud. We pay special attention to covariances among the different distance estimates. This most complete combination to date shows that all four methods are consistent within their random and systematic uncertainties.

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