Astropart.Phys.26:351-366,2007 The coupling of photons and baryons by Thomson scattering in the early
universe imprints features in both the Cosmic Microwave Background (CMB) and
matter power ...spectra. The former have been used to constrain a host of
cosmological parameters, the latter have the potential to strongly constrain
the expansion history of the universe and dark energy. Key to this program is
the means to localize the primordial features in observations of galaxy spectra
which necessarily involve galaxy bias, non-linear evolution and redshift space
distortions. We present calculations, based on mock catalogs produced from
high-resolution N-body simulations, which show the range of behaviors we might
expect of galaxies in the real universe. We investigate physically motivated
fitting forms which include the effects of non-linearity, galaxy bias and
redshift space distortions and discuss methods for analysis of upcoming data.
In agreement with earlier work, we find that a survey of several Gpc^3 would
constrain the sound horizon at z~1 to about 1%.
The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with new instrumentation and new surveys focused on Galactic structure and chemical evolution, measurements of the baryon ...oscillation feature in the clustering of galaxies and the quasar Ly alpha forest, and a radial velocity search for planets around ~8000 stars. This paper describes the first data release of SDSS-III (and the eighth counting from the beginning of the SDSS). The release includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap, bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a third of the Celestial Sphere. All the imaging data have been reprocessed with an improved sky-subtraction algorithm and a final, self-consistent photometric recalibration and flat-field determination. This release also includes all data from the second phase of the Sloan Extension for Galactic Understanding and Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars at both high and low Galactic latitudes. All the more than half a million stellar spectra obtained with the SDSS spectrograph have been reprocessed through an improved stellar parameters pipeline, which has better determination of metallicity for high metallicity stars.
Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the ...history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5 million massive galaxies and Lya forest spectra of 150,000 quasars, using the BAO feature of large scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z<0.7 and at z~2.5. SEGUE-2, which is now completed, measured medium-resolution (R=1800) optical spectra of 118,000 stars in a variety of target categories, probing chemical evolution, stellar kinematics and substructure, and the mass profile of the dark matter halo from the solar neighborhood to distances of 100 kpc. APOGEE will obtain high-resolution (R~30,000), high signal-to-noise (S/N>100 per resolution element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars, measuring separate abundances for ~15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. (Abridged)
We present the power spectrum of the reconstructed halo density field derived from a sample of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey Seventh Data Release (DR7). The halo ...power spectrum has a direct connection to the underlying dark matter power for k <= 0.2 h/Mpc, well into the quasi-linear regime. This enables us to use a factor of ~8 more modes in the cosmological analysis than an analysis with kmax = 0.1 h/Mpc, as was adopted in the SDSS team analysis of the DR4 LRG sample (Tegmark et al. 2006). The observed halo power spectrum for 0.02 < k < 0.2 h/Mpc is well-fit by our model: chi^2 = 39.6 for 40 degrees of freedom for the best fit LCDM model. We find \Omega_m h^2 * (n_s/0.96)^0.13 = 0.141^{+0.009}_{-0.012} for a power law primordial power spectrum with spectral index n_s and \Omega_b h^2 = 0.02265 fixed, consistent with CMB measurements. The halo power spectrum also constrains the ratio of the comoving sound horizon at the baryon-drag epoch to an effective distance to z=0.35: r_s/D_V(0.35) = 0.1097^{+0.0039}_{-0.0042}. Combining the halo power spectrum measurement with the WMAP 5 year results, for the flat LCDM model we find \Omega_m = 0.289 +/- 0.019 and H_0 = 69.4 +/- 1.6 km/s/Mpc. Allowing for massive neutrinos in LCDM, we find \sum m_{\nu} < 0.62 eV at the 95% confidence level. If we instead consider the effective number of relativistic species Neff as a free parameter, we find Neff = 4.8^{+1.8}_{-1.7}. Combining also with the Kowalski et al. (2008) supernova sample, we find \Omega_{tot} = 1.011 +/- 0.009 and w = -0.99 +/- 0.11 for an open cosmology with constant dark energy equation of state w.
Using a sample of approximately 14,000 z>2.1 quasars observed in the first year of the Baryon Oscillation Spectroscopic Survey (BOSS), we measure the three-dimensional correlation function of ...absorption in the Lyman-alpha forest. The angle-averaged correlation function of transmitted flux (F = exp(-tau)) is securely detected out to comoving separations of 60 Mpc/h, the first detection of flux correlations across widely separated sightlines. A quadrupole distortion of the redshift-space correlation function by peculiar velocities, the signature of the gravitational instability origin of structure in the Lyman-alpha forest, is also detected at high significance. We obtain a good fit to the data assuming linear theory redshift-space distortion and linear bias of the transmitted flux, relative to the matter fluctuations of a standard LCDM cosmological model (inflationary cold dark matter with a cosmological constant). At 95% confidence, we find a linear bias parameter 0.16<b<0.24 and redshift-distortion parameter 0.44<beta<1.20, at central redshift z=2.25, with a well constrained combination b(1+\beta)=0.336 +/- 0.012. The errors on beta are asymmetric, with beta=0 excluded at over 5 sigma confidence level. The value of beta is somewhat low compared to theoretical predictions, and our tests on synthetic data suggest that it is depressed (relative to expectations for the Lyman-alpha forest alone) by the presence of high column density systems and metal line absorption. These results set the stage for cosmological parameter determinations from three-dimensional structure in the Lyman-alpha forest, including anticipated constraints on dark energy from baryon acoustic oscillations.
The spectroscopic Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) galaxy sample represents the final set of galaxies observed using the original SDSS target selection criteria. We analyse the ...clustering of galaxies within this sample, including both the Luminous Red Galaxy (LRG) and Main samples, and also include the 2-degree Field Galaxy Redshift Survey (2dFGRS) data. Baryon Acoustic Oscillations are observed in power spectra measured for different slices in redshift; this allows us to constrain the distance--redshift relation at multiple epochs. We achieve a distance measure at redshift z=0.275, of r_s(z_d)/D_V(0.275)=0.1390+/-0.0037 (2.7% accuracy), where r_s(z_d) is the comoving sound horizon at the baryon drag epoch, D_V(z)=(1+z)^2D_A^2cz/H(z)^(1/3), D_A(z) is the angular diameter distance and H(z) is the Hubble parameter. We find an almost independent constraint on the ratio of distances D_V(0.35)/D_V(0.2)=1.736+/-0.065, which is consistent at the 1.1sigma level with the best fit Lambda-CDM model obtained when combining our z=0.275 distance constraint with the WMAP 5-year data. The offset is similar to that found in previous analyses of the SDSS DR5 sample, but the discrepancy is now of lower significance, a change caused by a revised error analysis and a change in the methodology adopted, as well as the addition of more data. Using WMAP5 constraints on Omega_bh^2 and Omega_ch^2, and combining our BAO distance measurements with those from the Union Supernova sample, places a tight constraint on Omega_m=0.286+/-0.018 and H_0 = 68.2+/-2.2km/s/Mpc that is robust to allowing curvature and non-Lambda dark energy. This result is independent of the behaviour of dark energy at redshifts greater than those probed by the BAO and supernova measurements. (abridged)
We use a sample of 53 massive early-type strong gravitational lens galaxies with well-measured redshifts (ranging from z=0.06 to 0.36) and stellar velocity dispersions (between 175 and 400 km/s) from ...the Sloan Lens ACS (SLACS) Survey to derive numerous empirical scaling relations. The ratio between central stellar velocity dispersion and isothermal lens-model velocity dispersion is nearly unity within errors. The SLACS lenses define a fundamental plane (FP) that is consistent with the FP of the general population of early-type galaxies. We measure the relationship between strong-lensing mass M_lens within one-half effective radius (R_e/2) and the dimensional mass variable M_dim = G^-1 sigma_e2^2 R_e/2 to be log_10 M_lens/10^11 M_Sun = (1.03 +/- 0.04) log_10 M_dim/10^11 M_Sun + (0.54 +/- 0.02) (where sigma_e2 is the projected stellar velocity dispersion within R_e/2). The near-unity slope indicates that the mass-dynamical structure of massive elliptical galaxies is independent of mass, and that the "tilt" of the SLACS FP is due entirely to variation in total (luminous plus dark) mass-to-light ratio with mass. Our results imply that dynamical masses serve as a good proxies for true masses in massive elliptical galaxies. Regarding the SLACS lenses as a homologous population, we find that the average enclosed 2D mass profile goes as log_10 M(<R)/M_dim = (1.10 +/- 0.09) log_10 R/R_e + (0.85 +/- 0.03), consistent with an isothermal (flat rotation curve) model when de-projected into 3D. This measurement is inconsistent with the slope of the average projected aperture luminosity profile at a confidence level greater than 99.9%, implying a minimum dark-matter fraction of f_DM = 0.38 +/- 0.07 within one effective radius. (abridged)
We present the definitive data for the full sample of 131 strong gravitational lens candidates observed with the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope by the Sloan Lens ...ACS (SLACS) Survey. All targets were selected for higher-redshift emission lines and lower-redshift continuum in a single Sloan Digital Sky Survey (SDSS) spectrum. The foreground galaxies are primarily of early-type morphology, with redshifts from approximately 0.05 to 0.5 and velocity dispersions from 160 km/s to 400 km/s; the faint background emission-line galaxies have redshifts ranging from about 0.2 to 1.2. We confirm 70 systems showing clear evidence of multiple imaging of the background galaxy by the foreground galaxy, as well as an additional 19 systems with probable multiple imaging. For 63 clear lensing systems, we present singular isothermal ellipsoid and light-traces-mass gravitational lens models fitted to the ACS imaging data. These strong-lensing mass measurements are supplemented by magnitudes and effective radii measured from ACS surface-brightness photometry and redshifts and velocity dispersions measured from SDSS spectroscopy. These data constitute a unique resource for the quantitative study of the inter-relations between mass, light, and kinematics in massive early-type galaxies. We show that the SLACS lens sample is statistically consistent with being drawn at random from a parent sample of SDSS galaxies with comparable spectroscopic parameters and effective radii, suggesting that the results of SLACS analyses can be generalized to the massive early-type population.
Reflected-wave transient voltages that result from fast insulated gate bipolar transistor voltage-source inverters have received considerable investigation. Modeling, simulation and attenuation of ...these transients require sophisticated motor and cable models. Most drive suppliers now provide combinations of passive and active solutions to mitigate the adverse effects of overvoltage stress, however, the costs of the passive solutions often exceed the cost of the drive. Another aspect of low-risetime devices, not examined to the extent of the overvoltage problem, is the resulting current from traveling waves. Current sensor fidelity limits the ability of modern drives to detect peak current and can result in current feedback distortion. This paper presents recent research into the response, modeling and construction of Hall-effect current sensors. Models for Hall-effect current sensors are introduced and compared. Experimental and simulation results demonstrate the complexity of the common current sensors employed in modern adjustable-speed drives. A comparison of the sensor response and the model's prediction demonstrates the difficulty associated with accurate current detection. Finally, the paper presents design guidelines to reduce the corrupting influence of high-frequency differential and common-mode currents.
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