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Spergel, David N.

Publications and source records attributed to Spergel, David N..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Two-Season Atacama Cosmology Telescope Polarimeter Lensing Power Spectrum

We report a measurement of the power spectrum of cosmic microwave background (CMB) lensing from two seasons of Atacama Cosmology Telescope polarimeter (ACTPol) CMB data. The CMB lensing power spectrum is extracted from both temperature and polarization data using quadratic estimators. We obtain results that are consistent with the expectation from the best-fit Planck CDM model over a range of multipoles L 80-2100, with an amplitude of lensing A(sub lens) = 1.06 +/- 0.15 stat +/- 0.06 sys relative to Planck. Our measurement of the CMB lensing power spectrum gives sigma 8 omega m(sup 0.25) = 0.643 +/- 0.054; including baryon acoustic oscillation scale data, we constrain the amplitude of density fluctuations to be sigma 8 = 0.831 +/- 0.053. We also update constraints on the neutrino mass sum. We verify our lensing measurement with a number of null tests and systematic checks, finding no evidence of significant systematic errors. This measurement relies on a small fraction of the ACTPol data already taken; more precise lensing results can therefore be expected from the full ACTPol data set.

Shewin, Blake D.↗
NASA NTRS2017

The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters

We present the temperature and polarization angular power spectra measuredby the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time datacollected during 2013-14 using two detector arrays at 149 GHz, from 548 deg(exp. 2) of sky onthe celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with Planck and WMAP data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the CDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters than the ACTPol temperature spectrum, including the baryon density, the acoustic peak angular scale, and the derived Hubble constant. The new ACTPol dataprovide information on damping tail parameters. The joint uncertainty on the number of neutrino species and the primordial helium fraction is reduced by 20% when adding ACTPol to Planck temperature data alone.

Louis, Thibaut↗
NASA NTRS2017

Cosmological Parameters From Pre-Planck CMB Measurements: A 2017 Update

We present cosmological constraints from the combination of the full mission nine-year WMAP release and small-scale temperature data from the pre-Planck Atacama Cosmology Telescope (ACT) and South Pole Telescope (SPT) generation of instruments. This is an update of the analysis presented in Calabrese et al. [Phys. Rev. D 87, 103012 (2013)], and highlights the impact on CDM cosmology of a 0.06 eV massive neutrino which was assumed in the Planck analysis but not in the ACTSPT analyses and a Planck-cleaned measurement of the optical depth to reionization. We show that cosmological constraints are now strong enough that small differences in assumptions about reionization and neutrino mass give systematic differences which are clearly detectable in the data. We recommend that these updated results be used when comparing cosmological constraints from WMAP, ACT and SPT with other surveys or with current and future full-mission Planck cosmology. Cosmological parameter chains are publicly available on the NASAs LAMBDA data archive.

Calabrese, Erminia↗
NASA NTRS2015

First Measurement of the Cross-Correlation of CMB Lensing and Galaxy Lensing

We measure the cross-correlation of cosmic microwave background (CMB) lensing convergence maps derived from Atacama Cosmology Telescope data with galaxy lensing convergence maps as measured by the Canada-France-Hawaii Telescope Stripe 82 Survey. The CMB-galaxy lensing cross power spectrum is measured for the first time with a significance of 4.2σ, which corresponds to a 12% constraint on the amplitude of density fluctuations at redshifts ∼0.9. With upcoming improved lensing data, this novel type of measurement will become a powerful cosmological probe, providing a precise measurement of the mass distribution at intermediate redshifts and serving as a calibrator for systematic biases in weak lensing measurements.

CMB-galzxy lensing cross power spectrum↗
NASA NTRS2014

The Primordial Inflation Explorer (PIXIE)

The Primordial Inflation Explorer is an Explorer-class mission to measure the gravity-wave signature of primordial inflation through its distinctive imprint on the linear polarization of the cosmic microwave background. PIXIE uses an innovative optical design to achieve background-limited sensitivity in 400 spectral channels spanning 2.5 decades in frequency from 30 GHz to 6 THz (1 cm to 50 micron wavelength). Multi-moded non-imaging optics feed a polarizing Fourier Transform Spectrometer to produce a set of interference fringes, proportional to the difference spectrum between orthogonal linear polarizations from the two input beams. Multiple levels of symmetry and signal modulation combine to reduce the instrumental signature and confusion from unpolarized sources to negligible levels. PIXIE will map the full sky in Stokes I, Q, and U parameters with angular resolution 2.6 deg and sensitivity 0.2 μK per 1 deg square pixel. The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r less than 10(exp −3) at 5 standard deviations. In addition, PIXIE will measure the absolute frequency spectrum to constrain physical processes ranging from inflation to the nature of the first stars to the physical conditions within the interstellar medium of the Galaxy. We describe the PIXIE instrument and mission architecture with an emphasis on the expected level of systematic error suppression.

Primordial Inflation Explorer is an Explorer-class↗
NASA NTRS2013

First Measurement of the Cross-Correlation of CMB Lensing and Galaxy Lensing

We measure the cross-correlation of cosmic microwave background lensing convergence maps derived from Atacama Cosmology Telescope data with galaxy lensing convergence maps as measured by the Canada-France-Hawaii Telescope Stripe 82 Survey. The CMB-galaxy lensing cross power spectrum is measured for the first time with a significance of 3.2σ, which corresponds to a 16% constraint on the amplitude of density fluctuations at redshifts ~ 0.9. With upcoming improved lensing data, this novel type of measurement will become a powerful cosmological probe, providing a precise measurement of the mass distribution at intermediate redshifts and serving as a calibrator for systematic biases in weak lensing measurements.

Hand, Nick↗
NASA NTRS2012

The Atacama Cosmology Telescope: Cross-Correlation of Cosmic Microwave Background Lensing and Quasars

We measure the cross-correlation of Atacama cosmology telescope cosmic microwave background (CMB) lensing convergence maps with quasar maps made from the Sloan Digital Sky Survey DR8 SDSS-XDQSO photometric catalog. The CMB lensing quasar cross-power spectrum is detected for the first time at a significance of 3.8 sigma, which directly confirms that the quasar distribution traces the mass distribution at high redshifts z > 1. Our detection passes a number of null tests and systematic checks. Using this cross-power spectrum, we measure the amplitude of the linear quasar bias assuming a template for its redshift dependence, and find the amplitude to be consistent with an earlier measurement from clustering; at redshift z ap 1.4, the peak of the distribution of quasars in our maps, our measurement corresponds to a bias of b = 2.5 +/- 0.6. With the signal-to-noise ratio on CMB lensing measurements likely to improve by an order of magnitude over the next few years, our results demonstrate the potential of CMB lensing crosscorrelations to probe astrophysics at high redshifts.

CMB lensing quasar cross-power spectrum↗
NASA NTRS2012

Power-Law Template for Infrared Point-Source Clustering

We perform a combined fit to angular power spectra of unresolved infrared (IR) point sources from the Planck satellite (at 217, 353, 545, and 857 GHz, over angular scales 100 approx < l approx < 2200), the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST; 250, 350, and 500 micron; 1000 approx < l approx < 9000), and from correlating BLAST and Atacama Cosmology Telescope (ACT; 148 and 218 GHz) maps. We find that the clustered power over the range of angular scales and frequencies considered is well fitted by a simple power law of the form C(sup clust)(sub l) varies as l (sub −n) with n = 1.25 +/- 0.06. While the IR sources are understood to lie at a range of redshifts, with a variety of dust properties, we find that the frequency dependence of the clustering power can be described by the square of a modified blackbody, ν(sup Beta)B(ν, T(sub eff) ), with a single emissivity index Beta = 2.20 +/- 0.07 and effective temperature T(sub eff) = 9.7 K. Our predictions for the clustering amplitude are consistent with existing ACT and South Pole Telescope results at around 150 and 220 GHz, as is our prediction for the effective dust spectral index, which we find to be alpha(sub 150-220) = 3.68 +/- 0.07 between 150 and 220 GHz. Our constraints on the clustering shape and frequency dependence can be used to model the IR clustering as a contaminant in cosmic microwave background anisotropy measurements. The combined Planck and BLAST data also rule out a linear bias clustering model.

cosmic background radiation↗
NASA NTRS2012

The Atacama Cosmology Telescope: ACT-CL J0102-4915 'EL GORDO', A Massive Merging Cluster at Redshift 0.87

We present a detailed analysis from new multi-wavelength observations of the exceptional galaxy cluster ACT-CL J0102−4915, likely the most massive, hottest, most X-ray luminous and brightest Sunyaev-Zel'dovich (SZ) effect cluster known at redshifts greater than 0.6. The Atacama Cosmology Telescope (ACT) collaboration discovered ACT-CL J0102−4915 as the most significant Sunyaev-Zeldovich (SZ) decrement in a sky survey area of 755 square degrees. Our VLT/FORS2 spectra of 89 member galaxies yield a cluster redshift, z = 0.870, and velocity dispersion, sigma(sub gal) = 1321+/-106 km s−1. Our Chandra observations reveal a hot and X-ray luminous system with an integrated temperature of T(sub X) = 14.5+/-1.0 keV and 0.5-2.0 keV band luminosity of L(sub X) = (2.19+/-0.11)×10(sup 45) h(sup −2)(sub 70) erg s−1. We obtain several statistically consistent cluster mass estimates; using empirical mass scaling relations with velocity dispersion, X-ray Y(sub X), and integrated SZ distortion, we estimate a cluster mass of M(sub 200a) = (2.16+/-0.32)×1015 h(sup −1)(sub 70) solar mass. We constrain the stellar content of the cluster to be less than 1% of the total mass, using Spitzer IRAC and optical imaging. The Chandra and VLT/FORS2 optical data also reveal that ACT-CL J0102−4915 is undergoing a major merger between components with a mass ratio of approximately 2 to 1. The X-ray data show significant temperature variations from a low of 6.6+/-0.7 keV at the merging low-entropy, high-metallicity, cool core to a high of 22+/-6 keV. We also see a wake in the X-ray surface brightness and deprojected gas density caused by the passage of one cluster through the other. Archival radio data at 843 MHz reveal diffuse radio emission that, if associated with the cluster, indicates the presence of an intense double radio relic, hosted by the highest redshift cluster yet. ACT-CL J0102−4915 is possibly a high-redshift analog of the famous Bullet Cluster. Such a massive cluster at this redshift is rare, although consistent with the standard ΛCDM cosmology in the lower part of its allowed mass range. Massive, highredshift mergers like ACT-CL J0102−4915 are unlikely to be reproduced in the current generation of numerical N-body cosmological simulations.

cosmology observations↗
NASA NTRS2011

The Atacama Cosmology Telescope: ACT-CL J0102-4215 "El Gordo," a Massive Merging Cluster at Redshift 0.87

We present a detailed analysis from new multi-wavelength observations of the exceptional galaxy cluster ACT-CL J0102-4915, likely the most massive, hottest, most X-ray luminous and brightest Sunyaev-Zel'dovich (SZ) effect cluster known at redshifts greater than 0.6. The Atacama Cosmology Telescope (ACT) collaboration discovered ACT-CL J0102-4915 as the most significant Sunyaev-Zeldovich (SZ) decrement in a sky survey area of 755 square degrees. Our VLT/FORS2 spectra of 89 member galaxies yield a cluster redshift, z = 0.870, and velocity dispersion, sigma(gal) +/- 1321 106 km s-1. Our Chandra observations reveal a hot and X-ray luminous system with an integrated temperature of T(X) = 14:5 +/- 0:1 keV and 0.5 2.0 keV band luminosity of L(X) = (2:19 0:11) 1045 h(exp -2)70erg s-1. We obtain several statistically consistent cluster mass estimates; using empirical mass scaling relations with velocity dispersion, X-ray Y(X) , and integrated SZ distortion, we estimate a cluster mass of M(200) = (2:16 +/- 0:32) 10(exp 15) h(exp-1) 70M compared to the Sun. We constrain the stellar content of the cluster to be less than 1% of the total mass, using Spitzer IRAC and optical imaging. The Chandra and VLT/FORS2 optical data also reveal that ACT-CL J0102-4915 is undergoing a major merger between components with a mass ratio of approximately 2 to 1. The X-ray data show significant temperature variations from a low of 6:6 +/- 0:7 keV at the merging low-entropy, high-metallicity, cool core to a high of 22 +/- 6 keV. We also see a wake in the X-ray surface brightness and deprojected gas density caused by the passage of one cluster through the other from which we estimate a merger speed of around 1300 km s(exp -1) for an assumed merger timescale of 1 Gyr. ACTCL J0102-4915 is possibly a high-redshift analog of the famous Bullet Cluster. Such a massive cluster at this redshift is rare, although consistent with the standard CDM cosmology in the lower part of its allowed mass range. Massive, high-redshift mergers like ACT-CL J0102-4915 are unlikely to be reproduced in the current generation of numerical N-body cosmological simulations.

Menanteau, Felipe↗
NASA NTRS2011

Power-Law Template for IR Point Source Clustering

We perform a combined fit to angular power spectra of unresolved infrared (IR) point sources from the Planck satellite (at 217,353,545 and 857 GHz, over angular scales 100 < I < 2200), the Balloonborne Large-Aperture Submillimeter Telescope (BLAST; 250, 350 and 500 microns; 1000 < I < 9000), and from correlating BLAST and Atacama Cosmology Telescope (ACT; 148 and 218 GHz) maps. We find that the clustered power over the range of angular scales and frequencies considered is well fit by a simple power law of the form C_l\propto I(sup -n) with n = 1.25 +/- 0.06. While the IR sources are understood to lie at a range of redshifts, with a variety of dust properties, we find that the frequency dependence of the clustering power can be described by the square of a modified blackbody, nu(sup beta) B(nu,T_eff), with a single emissivity index beta = 2.20 +/- 0.07 and effective temperature T_eff= 9.7 K. Our predictions for the clustering amplitude are consistent with existing ACT and South Pole Telescope results at around 150 and 220 GHz, as is our prediction for the effective dust spectral index, which we find to be alpha_150-220 = 3.68 +/- 0.07 between 150 and 220 GHz. Our constraints on the clustering shape and frequency dependence can be used to model the IR clustering as a contaminant in Cosmic Microwave Background anisotropy measurements. The combined Planck and BLAST data also rule out a linear bias clustering model.

Addison, Graeme E.↗
NASA NTRS2011

The Primordial Inflation Explorer (PIXIE) Mission

The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission to map the absolute intensity and linear polarization of the cosmic microwave background and diffuse astrophysical foregrounds over the full sky from frequencies 30 GHz to 6 THz (I cm to 50 I-tm wavelength). PIXIE uses a polarizing Michelson interferometer with 2.7 K optics to measure the difference spectrum between two orthogonal linear polarizations from two co-aligned beams. Either input can view either the sky or a temperature-controlled absolute reference blackbody calibrator. The multimoded optics and high etendu provide sensitivity comparable to kilo-pixel focal plane arrays, but with greatly expanded frequency coverage while using only 4 detectors total. PIXIE builds on the highly successful COBEIFIRAS design by adding large-area polarization-sensitive detectors whose fully symmetric optics are maintained in thermal equilibrium with the CMB. The highly symmetric nulled design provides redundant rejection of major sources of systematic uncertainty. The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r much less than 10(exp -3). PIXIE will also return a rich data set constraining physical processes ranging from Big Bang cosmology, reionization, and large-scale structure to the local interstellar medium. Keywords: cosmic microwave background, polarization, FTS, bolometer

Kogut, Alan J.↗
NASA NTRS1996

The Non-Axisymmetric Milky Way

The Dwek et al. model represents the current state-of-the-art model for the stellar structure of our Galaxy. The improvements we have made to this model take a number of forms: (1) the construction of a more detailed dust model so that we can extend our modeling to the galactic plane; (2) simultaneous fits to the bulge and the disk; (3) the construction of the first self-consistent model for a galactic bar; and (4) the development and application of algorithms for constructing nonparametric bar models. The improved Galaxy model has enabled a number of exciting science projects. In Zhao et al., we show that the number and duration of microlensing events seen by the OGLE and MACHO collaborations towards the bulge were consistent with the predictions of our bar model. In Malhotra et al., we constructed an infrared Tully-Fisher (TF) relation for the local group. We found the tightest TF relation ever seen in any band and in any group of galaxies. The tightness of the correlation places strong constraints on galaxy formation models and provides a independent check of the Cepheid distance scale.

Spergel, David N.↗
NASA NTRS1995

Hot gas in superclusters and microwave background distortions

Variations in the electron pressure can produce significant distortions of the cosmic microwave background radiation (CMBR) spectrum through the Sunyaev-Zel'dovich effect. In this paper, we compute the amplitude of these distortions in various cosmological scenarios using the results of hydrodynamical simulations combined with analytic theory. For reionized cold dark matter (CDM) with h = 0.5 probed with the OVRO experiment (Theta approximately = 0.1 deg), we find that the amplitude of these fluctuations is (Delta T/T)(sub rms) = 1 x 10(exp -5) (Omega(sub i)/0.06) if the experiment looks at a random part of the sky and 6 x 10(exp -6)(Omega(sub i)/(0.06) if bright areas are avoided. Here Omega is the density of ionized baryons in units of the critical density, rho(sub c) = 2.78 x 10(exp 11)h(exp 2)/cu Mpc. Primary fluctuations would generate (Delta T/T)(sub rms) approximately = 2 x 10(exp -6) for this model. These distortions could be a dominant source of CMBR anisotropics on small and intermediate angular scales. It is important to note that these signals are generated relatively recently, when nonlinear effects are improtant, and do not require early reionization. We also examine the contribution to anisotropies from the Doppler effect, in both the linear and nonlinear regimes. In this case, the bulk of the signal is generated before a redshift of 10, provided that the intercluster medium is ionized back to the surface of last scattering. On the smallest scales thermal effects are bigger, while, on larger scales the Doppler-induced fluctuations are greater with the exact boundary determined by the scenario. However, over a wide range of scales, the two signals are equal to within a factor of a few.

Persi, Fred M.↗
NASA NTRS1995

Microlensing by the galactic bar

We compute the optical depth and duration distribution of microlensing events towrd Baade's window in a model composed of a Galactic disk and a bar. The bar model is a self-consistent dynamical model built out of individual orbits that has been populated to be consistent with the COBE maps of the Galaxy and kinematic observations of the Galactic bulge. We find that most of the lenses are in the bulge with a line-of-sight distance 6.25 kpc (adopting R(sub 0) = 8 kpc). The microlensing optical depth of a 2 x 10(exp 10) solar mass bar plus a truncated disk is (2.2 +/- 0.45) x 10(exp -6), consistent with the large optical depth (3.2 +/- 1.2) x 10(exp -6) found by Udalski et al. (1994). This model optical depth is enhanced over the predictions of axisymmetric models by Kiraga & Paczynski (1994) by slightly more than a factor of 2, since the bar is elongated along the line of sight. The large Einstein radius and small transverse velocity dispersion also predict a longer event duration in the self-consistent bar model than in the Kiraga-Paczynski model. The event rate and duration distribution also depend on the lower mass cutoff of the lens mass function. With a 0.1 solar mass cutoff, five to seven events (depending on the contribution of disk lenses) with a logarithmic mean duration of 20 days are expected for the Optical Gravitational Lensing Experiment (OGLE) according to our model, while Udalski et al. (1994) observed nine events with durations from 8 to 62 days. On the other hand, if most of the lenses are brown dwarfs, our model predicts too many short-duration events. A Kolmogorov-Smirnov test finds only 7% probability for the model with 0.01 solar mass cutoff to be consistent with current data.

Zhao, Hongsheng↗
NASA NTRS1994

Signatures of bulge triaxiality from kinematics in Baade's window

We study a sample of 62 Baade's Window, (l,b) = (1, -4)deg, K giants that have published proper motions, radial velocity, and metallicity. Using R(sub 0) = 8 kpc, we construct the velocity ellipsoids, namely the 3x3 velocity dispersion tensors, for the metal rich stars ((Fe/H) greater than or equal to 0) and metal poor stars ((Fe/H) less than or equal to -0.2). After diagonalizing the tensor, we find a vertex deviation characteristic of a nonaxisymmetric system. Eigenvalues for the two velocity ellipsoids (sigma(sub 1), sigma(sub 2), sigma(sub 3)) are (126, 89, 65) +/- 13 km/s for the metal rich sample and (154, 77, 83) +/- 25 km/s for the metal poor sample with their long axes pointing to two nearly perpendicular directions (l(sub v), b(sub v)) = (-65 +/- 9 deg, +14 +/- 9 deg) and (l(sub v), b(sub v)) = (25 +/- 14 deg, -11 +/- 14 deg), respectively. The vertex deviations of the velocity ellipsoids cannot be consistently explained by any oblate model. We are able to reject the hypothesis that the metal poor and metal rich populations are drawn from the same distribution at better than the 97% confidence level. We populate orbits in a realistic bar potential with a Gaussian velocity distribution, allowing us to simulate and interpret observations. We conclude that the data are consistent with a triaxial bulge pointing towards (l,b) with l less than 0 deg and b = 0 deg as suggested by earlier work on gas dynamics and the observed light distribution. We also predict that low latitude (absolute value of b less than or equal to 4 deg) bulge fields should show the vertex deviation more strongly and would therefore be the best locations for future proper motion studies. In the classification scheme of Athanassoula et al. (1983) the metal rich stars appear to occupy the B-family orbits which rotate in the prograde sense in the rest frame and have boxy shapes that are aligned with and supporting the bar. The metal poor stars in the sample lag behind the metal rich bulge and appear to occupy R-family orbits which rotate in the retrograde sense in the rest frame. They have nearly round loop shapes and are aligned perpendicularly to the bar, hence limit the triaxiality of the bar potential. The correlations between the metallicity and the orbit families can develop if the bulge forms dissipatively on a sufficiently long time scale. However, it is difficult to explain such correlations if most stars in the inner Galaxy form during the violent relaxation phase.

Zhao, Hongsheng↗
NASA NTRS1994

Cosmic background radiation anisotropy in an open inflation, cold dark matter cosmogony

We compute the cosmic background radiation anisotropy, produced by energy-density fluctuations generated during an early epoch of inflation, in an open cosmological model based on the cold dark matter scenario. At Omega(sub 0) is approximately 0.3-0.4, the Cosmic Background Explorer (COBE) normalized open model appears to be consistent with most observations.

Kamionkowski, Marc↗