72 results on '"Spergel, David"'
Search Results
2. Ultra-light dark matter in ultra-faint dwarf galaxies.
- Author
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Calabrese, Erminia and Spergel, David N.
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DARK matter , *DWARF galaxies , *BARYONS , *SCALAR field theory , *STELLAR populations - Abstract
Cold Dark Matter (CDM) models struggle to match the observations at galactic scales. The tension can be reduced either by dramatic baryonic feedback effects or by modifying the particle physics of CDM. Here, we consider an ultra-light scalar field DM particle manifesting a wave nature below a DM particle mass-dependent Jeans scale. For DM mass m ~ 10-22 eV, this scenario delays galaxy formation and avoids cusps in the centre of the dark matter haloes. We use new measurements of half-light mass in ultra-faint dwarf galaxies Draco II and Triangulum II to estimate the mass of the DM particle in this model. We find that if the stellar populations are within the core of the density profile then the data are in agreement with a Wave Dark Matter model having a DM particle with m ~ 3.7-5.6 ? 10-22 eV. The presence of this extremely light particle will contribute to the formation of a central solitonic core replacing the cusp of a Navarro-Frenk-White profile and bringing predictions closer to observations of cored central density in dwarf galaxies. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
3. Cosmology Today.
- Author
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Spergel, David N.
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ASTRONOMICAL models , *METAPHYSICAL cosmology , *COSMIC background radiation , *PHYSICAL cosmology , *DARK matter , *DARK energy , *GALAXY clusters , *NEBULAE - Abstract
We seem to live in a simple but strange universe. Our basic cosmological model fits a host of astronomical observations with only five basic parameters: the age of the universe, the density of atoms, the density of matter, the initial "lumpiness" of the universe, and a parameter that describes whether this lumpiness is more pronounced on smaller physical scales. Our observations of the cosmic microwave background fluctuations determine these parameters with uncertainties of only 1 to 2 percent. The same model also provides an excellent fit to the large-scale clustering of galaxies and gas, the properties of galaxy clusters, observations of gravitational lensing, and supernova-based measurements of the Hubble relation. This model implies that we live in a strange universe: atoms make up only 4 percent of the visible universe, dark matter makes up 24 percent, and dark energy - energy associated with empty space - makes up 72 percent. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
4. Joint analysis of cluster number counts and weak lensing power spectrum to correct for the super-sample covariance.
- Author
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Takada, Masahiro and Spergel, David N.
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METAPHYSICAL cosmology , *ANALYSIS of covariance , *GAUSSIAN processes , *GRAVITATIONAL lenses , *STAR clusters - Abstract
A coherent over- or under-density contrast across a finite survey volume causes an upward- or downward fluctuation in the observed number of haloes. This fluctuation in halo number adds a significant co-variant scatter in the observed amplitudes of weak lensing power spectrum at non-linear, small scales – the so-called super-sample variance or the halo sample variance. In this paper, we show that by measuring both the number counts of clusters and the power spectrum in the same survey region, we can mitigate this loss of information and significantly enhance the scientific return from the upcoming surveys. First, using the halo model approach, we derive the cross-correlation between the halo number counts and the weak lensing power spectrum, taking into account the super-sample covariance effect, which well matches the distributions measured from 1000 realizations for a Λ-dominated cold dark matter model. Then we show that adding the observed number counts of massive haloes with M ≳ 1014 M⊙/h can significantly improve the information content of weak lensing power spectrum, almost recovering the Gaussian information up to lmax ≃ 1000, if the average mass profiles of the massive haloes are known, which can be estimated from stacked lensing. When combined with the halo number counts for M > 3 or 1 × 1014 M⊙ h−1, the improvement is up to a factor of 1.4 or 2 at lmax ≃ 1000–2000, equivalent to a factor of 2 or 4 times larger survey volume, compared to the power spectrum measurement alone. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
5. The cosmic microwave background a gravity wave detector.
- Author
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Spergel, David N.
- Subjects
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GRAVITY waves , *COSMIC background radiation , *ASTROPHYSICS - Abstract
Long wavelength gravity waves produce a distinctive signature of polarization fluctuations in the cosmic microwave background. With very sensitive experiments with minimal systematics, this signal is potentially detectable. Since the universe was transparent to gravity waves back to the Planck time, gravity wave observations are a probe of physics in the early universe and physics at very high energy scales. In this talk, I review the current status of microwave background experiments. I then discuss the coming generation of experiments that should be of detecting polarization fluctuations produce by scalar fluctuations. A future satellite experiment (beyond MAP and Planck) will likey be needed to detect tensor fluctuations. [ABSTRACT FROM AUTHOR]
- Published
- 2001
6. Planck data reconsidered.
- Author
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Spergel, David N., Flauger, Raphael, and Hložek, Renée
- Subjects
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PLANCK (Artificial satellite) , *DATA analysis , *COSMIC background radiation , *NEUTRINOS , *ASTRONOMICAL observations - Abstract
The tension between the best fit parameters derived by the Planck team and a number of other astronomical measurements suggests either systematics in the astronomical measurements, systematics in the Planck data, the need for new physics, or a combination thereof. We reanalyze the Planck data and find that the 217 GHz × 217 GHz detector set spectrum used in the Planck analysis is responsible for some of this tension. We use a map-based foreground cleaning procedure, relying on a combination of 353 GHz and 545 GHz maps to reduce residual foregrounds in the intermediate frequency maps used for cosmological inference. For our baseline data analysis, which uses 47% of the sky and makes use of both 353 and 545 GHz data for foreground cleaning, we find the ΛCDM cosmological parameters Ωch2 = 0.1170 ± 0.0025, ns = 0.9686 ± 0.0069, H0 = 68.0 ± 1.1 kms-1?Mpc-1, Ωbh² = 0.02197 ± 0.00026, ln1010As = 3.082 ± 0.025, and τ = 0.090 ± 0.013. While in broad agreement with the results reported by the Planck team, these revised parameters imply a universe with a lower matter density of Ωm = 0.302 ± 0.015, and parameter values generally more consistent with pre-Planck CMB analyses and astronomical observations. We compare our cleaning procedure with the foreground modeling used by the Planck team and find good agreement. The difference in parameters between our analysis and that of the Planck team is mostly due to our use of cross-spectra from the publicly available survey maps instead of their use of the detector set cross-spectra which include pixels only observed in one of the surveys. We show evidence suggesting residual systematics in the detector set spectra used in the Planck likelihood code, which is substantially reduced for our spectra. Using our cleaned survey cross-spectra, we recompute the limit on neutrino species and find Neff = 3.34 ± 0.35. We also recompute limits on the ns-r plane, and neutrino mass constraints. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
7. THRESHOLD PROBABILITY FUNCTIONS AND THERMAL INHOMOGENEITIES IN THE Lyα FOREST.
- Author
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KHEE-GAN LEE and SPERGEL, DAVID N.
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PROBABILITY theory , *DISTRIBUTION (Probability theory) , *DENSITY of stars , *TEMPERATURE of stars , *STELLAR spectra , *PDF (Computer file format) - Abstract
We introduce to astrophysics the threshold probability functions S2, C2, and D2 first derived by Torquato et al., which effectively samples the flux probability distribution function (PDF) of the Lyα forest at different spatial scales. These statistics are tested on mock Lyα forest spectra based on various toy models for He II reionization, with homogeneous models with various temperature-density relations as well as models with temperature inhomogeneities. These mock samples have systematics and noise added to simulate the latest Sloan Digital Sky Survey Data Release 7 (SDSS DR7) data. We find that the flux PDF from SDSS DR7 can be used to constrain the temperature-density relation γ (where T ∝ (1 + Δ)γ-1) of the intergalactic medium (1GM) at z = 2.5 to a precision of Δγ = 0.2 at ~4ι confidence. The flux PDF is degenerate to temperature inhomogeneities in the 1GM arising from He ii reionization, but we find S2 can detect these inhomogeneities at ~3ι, with the assumption that the flux continuum of the Lyα forest can be determined to 9% accuracy, approximately the error from current fitting methods, if the flux continuum can be determined to 3% accuracy, then S2 is capable of constraining the characteristic scale of temperature inhomogeneities, with ~4ι differentiation between toy models with hot bubble radii of 50 h-1 Mpc and 25 h-1 Mpc. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
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8. The dark side of cosmology: Dark matter and dark energy.
- Author
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Spergel, David N.
- Subjects
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METAPHYSICAL cosmology , *DARK matter , *DARK energy , *STELLAR evolution , *GENERAL relativity (Physics) , *MILKY Way - Abstract
A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of "dark matter," a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of "dark energy," energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
9. COSMIC STRINGS: TOPOLOGICAL FOSSILS OF THE HOT BIG BANG.
- Author
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Press, William H. and Spergel, David N.
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COSMIC background radiation , *METAPHYSICAL cosmology , *GALAXIES , *ASTRONOMY , *INTERSTELLAR medium - Abstract
This article focuses on cosmic strings, the stable remains of an ultradense state of matter, completely different from any state that exists in bulk, and the idea of topological conservation. Modern field theories represent matter by a set of quantum fields or operators. In the semiclassical limit, these operators can be considered to be ordinary numbers, representing the wave-amplitude or probability density of each field at every space-time point. Cosmic strings occur when there is a slightly more complicated symmetry. A description of the basic mechanical behavior of a string is described in this article. The evolution of cosmic strings in the early universe is also described in this article. Observations of the cosmic background radiation reveal that the early universe was highly homogeneous at a redshift z of about 1300. The existence of galaxies and the clustering of galaxies on large scales suggest that the universe has become rather inhomogeneous on scales as large as 1 percent of the horizon size, and perhaps on even larger scales. Cosmic strings provide an alternative scenario for the formation of large-scale structure. According this picture, the surviving cosmic-string loops serve as nonlinear seeds and accrete both dark matter and baryons. Future observations may reveal the existence of cosmic strings directly. Cosmic strings curve space: While a straight string does not attract matter, it does curve space-time. In effect, it cuts wedge out of space-time and produces a conical universe.
- Published
- 1989
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10. The age of the universe.
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Spergel, David N. and Bolte, Michael
- Subjects
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BIG bang theory - Abstract
Summarizes a symposium on the big bang theory that was one of the Frontiers of Science symposia, held November 2-4, 1995, at the Arnold and Mabel Beckman Center of the National Academy of Sciences and Engineering in Irvine, California. What is the big bang theory; Number of successes which the theory had; Potential crisis faced by the model; Description of efforts to measure the stars.
- Published
- 1997
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11. What Is the Price of Abandoning Dark Matter? Cosmological Constraints on Alternative Gravity Theories.
- Author
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Pardo, Kris and Spergel, David N.
- Subjects
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DARK matter , *GREEN'S functions , *GRAVITY , *GALACTIC redshift , *COSMIC background radiation , *MICROWAVE measurements , *BARYONS - Abstract
Any successful alternative gravity theory that obviates the need for dark matter must fit our cosmological observations. Measurements of microwave background polarization trace the large-scale baryon velocity field at recombination and show very strong O(1) baryon acoustic oscillations. Measurements of the large-scale structure of galaxies at low redshift show much weaker features in the spectrum. If the alternative gravity theory's dynamical equations for the growth rate of structure are linear, then the density field growth can be described by a Green's function: δ(→x,t)=δ(→x,t')G(x,t,t'). We show that the Green's function G(x,t,t') must have dramatic features that erase the initial baryon oscillations. This implies an acceleration law that changes sign on the ∼150 Mpc scale. On the other hand, if the alternative gravity theory has a large nonlinear term that couples modes on different scales, then the theory would predict large-scale non-Gaussian features in large-scale structure. These are not seen in the distribution of galaxies nor in the distribution of quasars. No proposed alternative gravity theory for dark matter seems to satisfy these constraints. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
12. Extreme gas pressures in the galactic bulge.
- Author
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Spergel, David N. and Blitz, Leo
- Subjects
- *
ASTRONOMY - Abstract
States that molecular gas at the innermost regions of the Galactic Center must be in a very different state from the interstellar medium in the solar neighbor hood. Evidence for the existence of high gas pressure in the inner 500 parsecs of the Galaxy; Diffuse CS emission at the Galactic Center; Details.
- Published
- 1992
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13. Measuring the topology of the universe.
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Cornish, Neil J., Spergel, David N., and Starkman, Glenn D.
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ASTRONOMICAL observations - Abstract
Observes microwave background fluctuations with reference to the geometry of the universe and the topology of the universe. Description of the topology of the universe; Effects of topology on the universe; Methodology used in these observations.
- Published
- 1998
- Full Text
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14. Effective halo model: Creating a physical and accurate model of the matter power spectrum and cluster counts.
- Author
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Philcox, Oliver H. E., Spergel, David N., and Villaescusa-Navarro, Francisco
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POWER spectra , *SPEED of sound , *GRAVITATIONAL lenses , *PERTURBATION theory , *COVARIANCE matrices , *COSMIC background radiation - Abstract
We introduce a physically motivated model of the matter power spectrum, based on the halo model and perturbation theory. This model achieves 1% accuracy on all k -scales between k = 0.02 h Mpc-1 to k = 1h Mpc-1. Our key ansatz is that the number density of halos depends on the nonlinear density contrast filtered on some unknown scale R. Using the effective field theory of large scale structure to evaluate the two-halo term, we obtain a model for the power spectrum with only two fitting parameters: R and the effective "sound speed," which encapsulates small-scale physics. This is tested with two suites of cosmological simulations across a broad range of cosmologies and found to be highly accurate. Due to its physical motivation, the statistics can be easily extended beyond the power spectrum; we additionally derive the one-loop covariance matrices of cluster counts and their combination with the matter power spectrum. This yields a significantly better fit to simulations than previous models, and includes a new model for supersample effects, which is rigorously tested with separate universe simulations. At low redshift, we find a significant (~10%) exclusion covariance from accounting for the finite size of halos which has not previously been modeled. Such power spectrum and covariance models will enable joint analysis of upcoming large-scale structure surveys, gravitational lensing surveys, and cosmic microwave background maps on scales down to the nonlinear scale. We provide a publicly released python code. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
15. Teaching Neural Networks to Generate Fast Sunyaev–Zel'dovich Maps.
- Author
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Thiele, Leander, Villaescusa-Navarro, Francisco, Spergel, David N., Nelson, Dylan, and Pillepich, Annalisa
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GALAXY formation , *CONVOLUTIONAL neural networks , *ELECTRON distribution , *ELECTRON density , *DISTRIBUTION (Probability theory) , *DARK matter - Abstract
The thermal Sunyaev–Zel'dovich (tSZ) and the kinematic Sunyaev–Zel'dovich (kSZ) effects trace the distribution of electron pressure and momentum in the hot universe. These observables depend on rich multiscale physics, thus, simulated maps should ideally be based on calculations that capture baryonic feedback effects such as cooling, star formation, and other complex processes. In this paper, we train deep convolutional neural networks with a U-Net architecture to map from the three-dimensional distribution of dark matter to electron density, momentum, and pressure at ∼100 kpc resolution. These networks are trained on a combination of the TNG300 volume and a set of cluster zoom-in simulations from the IllustrisTNG project. The neural nets are able to reproduce the power spectrum, one-point probability distribution function, bispectrum, and cross-correlation coefficients of the simulations more accurately than the state-of-the-art semianalytical models. Our approach offers a route to capture the richness of a full cosmological hydrodynamical simulation of galaxy formation with the speed of an analytical calculation. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
16. Measuring the duration of last scattering.
- Author
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Hadzhiyska, Boryana and Spergel, David
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PHYSICAL cosmology - Abstract
The cosmic microwave background (CMB) fluctuations effectively measure the basic properties of the Universe during the recombination epoch. CMB measurements fix the distance to the surface of last scatter, the sound horizon of the baryon-photon fluid, and the fraction of the energy density in relativistic species. We show that the microwave background observations can also very effectively constrain the thickness of the last scattering surface, which is directly related to the ratio of the small-scale E-mode polarization signal to the small-scale temperature signal. The current cosmological data enable a ∼0.1% measurement of the thickness of the surface of last scatter: 19±0.065 Mpc. This constraint is relatively model independent, so it can provide a new metric for systematic errors and an independent test of the ΛCDM model. On the other hand, it is a sensitive tool for testing models which affect the reionization history of the Universe such as models with annihilating dark matter and varying fundamental constants (e.g., the fine-structure constant, αEM, and electron rest mass, me) and as such can provide a viable method to constrain them. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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17. How Do Galaxy Properties Affect Void Statistics?
- Author
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Panchal, Rushy R., Pisani, Alice, and Spergel, David N.
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GALAXY formation , *INTEREST rates , *GALAXIES , *STAR formation , *DARK matter - Abstract
Using mapping from dark matter halos to galaxy properties based on hydrodynamical simulations, we explore the impact of galaxy properties on the void size function and the void–galaxy correlation function. We replicate the properties of galaxies from Illustris on MassiveNus halos, to perform both luminosity and star formation rate cuts on MassiveNus halos. We compare the impact of such cuts on void properties with respect to cuts on halo mass (as usually performed on halo catalogs driven from N-body simulations). We find that void catalogs built from luminosity-selected galaxies and halos are consistent within errors, while void catalogs built from star formation rate-selected galaxies differ from void catalogs built on halos. We investigate the reason for this difference. Our work suggests that voids built on galaxy catalogs (selected through luminosity cuts) can be reliably studied using halos in dark matter simulations. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
18. Cosmology: The oldest cosmic light.
- Author
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Spergel, David and Keating, Brian
- Subjects
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COSMIC background radiation , *LIGHT , *BIG bang theory , *PHOTONS ,UNIVERSE - Abstract
The article provides information on the cosmic microwave background (CMB), a faint glow of light left over from the Big Bang. It is noted that the phenomenon fills the entire sky and records the early history of the Universe. Topics covered include the cosmic background radiation, ancient CMB photons and gravitational waves.
- Published
- 2015
- Full Text
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19. Small-scale modification to the lensing kernel.
- Author
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Hadzhiyska, Boryana, Spergel, David, and Dunkley, Joanna
- Subjects
- *
COSMIC background radiation , *GRAVITATIONAL lenses , *QUANTUM fluctuations - Abstract
Calculations of the cosmic microwave background (CMB) lensing power implemented into the standard cosmological codes such as camb and class usually treat the surface of last scatter as an infinitely thin screen. However, since the CMB anisotropies are smoothed out on scales smaller than the diffusion length due to the effect of Silk damping, the photons which carry information about the small-scale density distribution come from slightly earlier times than the standard recombination time. The dominant effect is the scale dependence of the mean redshift associated with the fluctuations during recombination. We find that fluctuations at k = 0.01 Mpc-1 come from a characteristic redshift of z ≈ 1090, while fluctuations at k = 0.3 Mpc-1 come from a characteristic redshift of z ≈ 1130. We then estimate the corrections to the lensing kernel and the related power spectra due to this effect. We conclude that neglecting it would result in a deviation from the true value of the lensing kernel at the half percent level at small CMB scales. For an all-sky, noise-free experiment, this corresponds to a ~ 0.1σ shift in the observed temperature power spectrum on small scales (2500 ≲ l ≲ 4000). [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
20. The SZ flux-mass (Y–M) relation at low-halo masses: improvements with symbolic regression and strong constraints on baryonic feedback.
- Author
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Wadekar, Digvijay, Thiele, Leander, Hill, J Colin, Pandey, Shivam, Villaescusa-Navarro, Francisco, Spergel, David N, Cranmer, Miles, Nagai, Daisuke, Anglés-Alcázar, Daniel, Ho, Shirley, and Hernquist, Lars
- Subjects
- *
COSMIC background radiation , *VIRIAL theorem , *ACTIVE galactic nuclei , *GALAXY clusters , *LARGE scale structure (Astronomy) - Abstract
Feedback from active galactic nuclei (AGNs) and supernovae can affect measurements of integrated Sunyaev–Zeldovich (SZ) flux of haloes (Y SZ) from cosmic microwave background (CMB) surveys, and cause its relation with the halo mass (Y SZ– M) to deviate from the self-similar power-law prediction of the virial theorem. We perform a comprehensive study of such deviations using CAMELS, a suite of hydrodynamic simulations with extensive variations in feedback prescriptions. We use a combination of two machine learning tools (random forest and symbolic regression) to search for analogues of the Y – M relation which are more robust to feedback processes for low masses (|$M\lesssim 10^{14}\, \mathrm{ h}^{-1} \, \mathrm{ M}_\odot$|); we find that simply replacing Y → Y (1 + M */ M gas) in the relation makes it remarkably self-similar. This could serve as a robust multiwavelength mass proxy for low-mass clusters and galaxy groups. Our methodology can also be generally useful to improve the domain of validity of other astrophysical scaling relations. We also forecast that measurements of the Y – M relation could provide per cent level constraints on certain combinations of feedback parameters and/or rule out a major part of the parameter space of supernova and AGN feedback models used in current state-of-the-art hydrodynamic simulations. Our results can be useful for using upcoming SZ surveys (e.g. SO, CMB-S4) and galaxy surveys (e.g. DESI and Rubin) to constrain the nature of baryonic feedback. Finally, we find that the alternative relation, Y – M *, provides complementary information on feedback than Y – M. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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21. EXTREME SPIN.
- Author
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Kruesi, Liz, Spergel, David, Weaver, Hal, and Brenneman, Laura
- Subjects
- *
BLACK holes , *HIGH temperatures - Abstract
The article offers answers to astronomy questions on topics including measurement of black hole spin, the highest possible temperature, and the New Horizons spacecraft's mission.
- Published
- 2014
22. THE GAIA INERTIAL REFERENCE FRAME AND THE TILTING OF THE MILKY WAY DISK.
- Author
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Perryman, Michael, Spergel, David N., and Lindegren, Lennart
- Subjects
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MILKY Way , *ASTROMETRY , *GALAXY formation , *STAR catalogs , *CELESTIAL reference systems - Abstract
While the precise relationship between the Milky Way disk and the symmetry planes of the dark matter halo remains somewhat uncertain, a time-varying disk orientation with respect to an inertial reference frame seems probable. Hierarchical structure formation models predict that the dark matter halo is triaxial and tumbles with a characteristic rate of ∼2 rad (∼30 μas yr–1). These models also predict a time-dependent accretion of gas, such that the angular momentum vector of the disk should be misaligned with that of the halo. These effects, as well as tidal effects of the LMC, will result in the rotation of the angular momentum vector of the disk population with respect to the quasar reference frame. We assess the accuracy with which the positions and proper motions from Gaia can be referred to a kinematically non-rotating system, and show that the spin vector of the transformation from any rigid self-consistent catalog frame to the quasi-inertial system defined by quasars should be defined to better than 1 μas yr–1. Determination of this inertial frame by Gaia will reveal any signature of the disk orientation varying with time, improve models of the potential and dynamics of the Milky Way, test theories of gravity, and provide new insights into the orbital evolution of the Sagittarius dwarf galaxy and the Magellanic Clouds. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
23. A direct measure of free electron gas via the kinematic Sunyaev-Zel'dovich effect in Fourier-space analysis.
- Author
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Sugiyama, Naonori S., Okumura, Teppei, and Spergel, David N.
- Subjects
- *
SUNYAEV-Zel'dovich effect , *POWER spectra , *KINEMATICS , *ELECTRON gas , *OPTICAL depth (Astrophysics) , *ASTRONOMICAL photometry - Abstract
We present the measurement of the kinematic Sunyaev-Zel'dovich (kSZ) effect in Fourier space, rather than in real space. We measure the density-weighted pairwise kSZ power spectrum, the first use of this promising approach, by cross-correlating a cleaned cosmicmicrowave background (CMB) temperature map, which jointly uses both Planck Release 2 and Wilkinson Microwave Anisotropy Probe nine-year data, with the two galaxy samples, CMASS and LOWZ, derived from the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12. To estimate the CMB temperature distortion associated with each galaxy, we apply an aperture photometry filter. With the current data, we constrain the average optical depth τ multiplied by the ratio of the Hubble parameter at redshift z and the present day, E = H/H0; we find τE = (3.95 ± 1.62) × 10-5 for LOWZ, which corresponds to the statistical significance of S/N = 2.44, and τE = (1.25 ± 1.06) × 10-5 for CMASS, which is consistent with a null hypothesis of no signal. While this analysis results in the kSZ signals with only evidence for a detection, the combination of future CMB and spectroscopic galaxy surveys should enable precision measurements. We estimate that the combination of CMB-S4 and data from Dark Energy Spectroscopic Instrument should yield detections of the kSZ signal with S/N = 70- 100, depending on the resolution of CMB-S4. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
24. A direct measure of free electron gas via the kinematic Sunyaev-Zel'dovich effect in Fourier-space analysis.
- Author
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Sugiyama, Naonori S., Teppei Okumura, and Spergel, David N.
- Subjects
- *
GALAXY spectra , *SUNYAEV-Zel'dovich effect , *ELECTRON gas , *HUBBLE constant , *COSMIC background radiation , *ASTRONOMICAL photometry - Abstract
We present the measurement of the kinematic Sunyaev-Zel'dovich (kSZ) effect in Fourier space, rather than in real space. We measure the density-weighted pairwise kSZ power spectrum, the first use of this promising approach, by cross-correlating a cleaned cosmicmicrowave background (CMB) temperature map, which jointly uses both Planck Release 2 and Wilkinson Microwave Anisotropy Probe nine-year data, with the two galaxy samples, CMASS and LOWZ, derived from the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12. To estimate the CMB temperature distortion associated with each galaxy, we apply an aperture photometry filter. With the current data, we constrain the average optical depth τ multiplied by the ratio of the Hubble parameter at redshift z and the present day, E = H/H0; we find τE = (3.95 ± 1.62) x 10-5 for LOWZ, which corresponds to the statistical significance of S/N = 2.44 and τE = (1.25 ± 1.06) x 10-5 for CMASS, which is consistent with a null hypothesis of no signal. While this analysis results in the kSZ signals with only evidence for a detection, the combination of future CMB and spectroscopic galaxy surveys should enable precision measurements. We estimate that the combination of CMB-S4 and data from Dark Energy Spectroscopic Instrument should yield detections of the kSZ signal with S/N = 70- 100, depending on the resolution of CMB-S4. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
25. The epoch of galaxy formation.
- Author
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Spergel, David N., Lilly, Simon J., and Steidel, Charles
- Subjects
- *
GALAXY formation - Abstract
Presents the summary of a symposium session on the formation of galaxies as part of the 1996 Frontiers in Science series. Technological advances that enable astronomers to study galaxy formation and evolution; Star formation rate; Redshift of the spectral lines; Lack of evidence for evolution in the red components of galaxies, spheroids and ellipticals.
- Published
- 1997
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26. Inferring Halo Masses with Graph Neural Networks.
- Author
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Villanueva-Domingo, Pablo, Villaescusa-Navarro, Francisco, Anglés-Alcázar, Daniel, Genel, Shy, Marinacci, Federico, Spergel, David N., Hernquist, Lars, Vogelsberger, Mark, Dave, Romeel, and Narayanan, Desika
- Subjects
- *
PROPERTIES of matter , *STELLAR mass , *PHASE space , *ASTROPHYSICS - Abstract
Understanding the haloâ€"galaxy connection is fundamental in order to improve our knowledge on the nature and properties of dark matter. In this work, we build a model that infers the mass of a halo given the positions, velocities, stellar masses, and radii of the galaxies it hosts. In order to capture information from correlations among galaxy properties and their phase space, we use Graph Neural Networks (GNNs), which are designed to work with irregular and sparse data. We train our models on galaxies from more than 2000 state-of-the-art simulations from the Cosmology and Astrophysics with MachinE Learning Simulations project. Our model, which accounts for cosmological and astrophysical uncertainties, is able to constrain the masses of the halos with a âĽ0.2 dex accuracy. Furthermore, a GNN trained on a suite of simulations is able to preserve part of its accuracy when tested on simulations run with a different code that utilizes a distinct subgrid physics model, showing the robustness of our method. The PyTorch Geometric implementation of the GNN is publicly available on GitHub (https://github.com/PabloVD/HaloGraphNet). [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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27. Nation needs recovery plan for science faculty jobs.
- Author
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Spergel, David
- Subjects
- *
UNIVERSITY faculty , *FINANCIAL crises , *GOVERNMENT aid to education , *SCIENCE education (Higher) , *ECONOMICS - Abstract
The article discusses the decline in open, college-science faculty positions associated with the economic crisis. Mentioned factors include declining endowments, institutional unwillingness to raise tuition costs, and decisions by older professors to postpone retirement. It calls on the U.S. Congress to allocate part of its science spending to the creation of open positions for junior faculty.
- Published
- 2009
- Full Text
- View/download PDF
28. THE GEOMETRY OF THE UNIVERSE.
- Author
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Bucher, Martin A. and Spergel, David N.
- Subjects
- *
COSMOGRAPHY , *DIMENSIONS , *METAPHYSICAL cosmology , *SPACE sciences , *ASTRONOMY , *ASTROPHYSICS , *GEOMETRY , *MATHEMATICAL geography - Abstract
If the universe had an "outside" and people could view it from that perspective, cosmology would be much easier. Lacking these gifts, astronomers must infer the basic shape of the universe from its geometric properties. Everyday experience indicates that space is Euclidean. Parallel lines never meet, triangles span 180 degrees and so on. But it would be wrong to assume that the universe is Euclidean on large scales, just as it would be wrong to conclude that the earth is flat just because a small patch of it looks flat. In a spherical universe, as on the earth's surface, parallel lines eventually meet, triangles can span up to 540 degrees, and the circumference of a circle is smaller than 2πr. Because the space curves back on itself, the spherical universe is finite. In a hyperbolic universe, parallel lines diverge, triangles have less than 180 degrees, and the circumference of a circle is larger than 2πr.
- Published
- 2002
29. The High Latitude Spectroscopic Survey on the Nancy Grace Roman Space Telescope.
- Author
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Wang, Yun, Zhai, Zhongxu, Alavi, Anahita, Massara, Elena, Pisani, Alice, Benson, Andrew, Hirata, Christopher M., Samushia, Lado, Weinberg, David H., Colbert, James, Doré, Olivier, Eifler, Tim, Heinrich, Chen, Ho, Shirley, Krause, Elisabeth, Padmanabhan, Nikhil, Spergel, David, and Teplitz, Harry I.
- Subjects
- *
GALAXY formation , *SPACE telescopes , *LATITUDE , *DARK energy , *ROMANS , *REDSHIFT - Abstract
The Nancy Grace Roman Space Telescope will conduct a High Latitude Spectroscopic Survey (HLSS) over a large volume at high redshift, using the near-IR grism (1.0â€"1.93 ÎĽ m, R = 435â€"865) and the 0.28 deg2 wide-field camera. We present a reference HLSS that maps 2000 deg2 and achieves an emission-line flux limit of 10â'16 erg sâ'1 cmâ'2 at 6.5 Ď, requiring âĽ0.6 yr of observing time. We summarize the flowdown of the Roman science objectives to the science and technical requirements of the HLSS. We construct a mock redshift survey over the full HLSS volume by applying a semianalytic galaxy formation model to a cosmological N -body simulation and use this mock survey to create pixel-level simulations of 4 deg2 of HLSS grism spectroscopy. We find that the reference HLSS would measure âĽ10 million H α galaxy redshifts that densely map large-scale structure at z = 1â€"2 and 2 million [O iii ] galaxy redshifts that sparsely map structures at z = 2â€"3. We forecast the performance of this survey for measurements of the cosmic expansion history with baryon acoustic oscillations and the growth of large-scale structure with redshift-space distortions. We also study possible deviations from the reference design and find that a deep HLSS at f line > 7 Ă— 10â'17 erg sâ'1 cmâ'2 over 4000 deg2 (requiring âĽ1.5 yr of observing time) provides the most compelling stand-alone constraints on dark energy from Roman alone. This provides a useful reference for future optimizations. The reference survey, simulated data sets, and forecasts presented here will inform community decisions on the final scope and design of the Roman HLSS. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
30. PROBING PATCHY REIONIZATION THROUGH τ-21 cm CORRELATION STATISTICS.
- Author
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Meerburg, P. Daniel, Dvorkin, Cora, and Spergel, David N.
- Subjects
- *
COSMIC background radiation , *METAPHYSICAL cosmology , *STARS , *PHOTON emission , *SIGNAL-to-noise ratio - Abstract
We consider the cross-correlation between free electrons and neutral hydrogen during the epoch of reionization (EoR). The free electrons are traced by the optical depth to reionization τ, while the neutral hydrogen can be observed through 21 cm photon emission. As expected, this correlation is sensitive to the detailed physics of reionization. Foremost, if reionization occurs through the merger of relatively large halos hosting an ionizing source, the free electrons and neutral hydrogen are anticorrelated for most of the reionization history. A positive contribution to the correlation can occur when the halos that can form an ionizing source are small. A measurement of this sign change in the cross-correlation could help disentangle the bias and the ionization history. We estimate the signal-to-noise ratio of the cross-correlation using the estimator for inhomogeneous reionization proposed by Dvorkin and Smith. We find that with upcoming radio interferometers and cosmic microwave background (CMB) experiments, the cross-correlation is measurable going up to multipoles ℓ ∼ 1000. We also derive parameter constraints and conclude that, despite the foregrounds, the cross-correlation provides a complementary measurement of the EoR parameters to the 21 cm and CMB polarization autocorrelations expected to be observed in the coming decade. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
31. Strongly-interacting ultralight millicharged particles.
- Author
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Alexander, Stephon, McDonough, Evan, and Spergel, David N.
- Subjects
- *
BARYONS , *BARYON number , *QUARK matter , *NONABELIAN groups , *DARK matter , *ANDREEV reflection , *COOPER pair - Abstract
We consider the implications of an ultra-light fermionic dark matter candidate that carries baryon number. This naturally arises if dark matter has a small charge under standard model baryon number whilst having an asymmetry equal and opposite to that in the visible universe. A prototypical model is a theory of dark baryons of a non-Abelian gauge group, i.e., a dark Quantum Chromo-Dynamics (QCD). For sub-eV dark baryon masses, the inner region of dark matter halos is naturally at 'nuclear density', allowing for the formation of exotic states of matter, akin to neutron stars. The Tremaine-Gunn lower bound on the mass of fermionic dark matter, i.e., the dark baryons, is violated by the strong short-range self-interactions, cooling via emission of light dark pions, and the Cooper pairing of dark quarks that occurs at densities that are high relative to the (ultra-low) dark QCD scale. We develop the astrophysics of these STrongly-interacting Ultra-light Millicharged Particles (STUMPs) utilizing the equation of state of dense quark matter, and find halo cores consistent with observations of dwarf galaxies. These cores are prevented from core-collapse by pressure of the 'neutron star', which suggests ultra-light dark QCD as a resolution to core-cusp problem of collisionless cold dark matter. The model is distinguished from ultra-light bosonic dark matter through direct detection and collider signatures, as well as by phenomena associated with superconductivity, such as Andreev reflection and superconducting vortices. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
32. WISE measurement of the integrated Sachs-Wolfe effect.
- Author
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Ferrara, Simone, Sherwin, Blake D., and Spergel, David N.
- Subjects
- *
DARK energy , *COSMIC background radiation , *GRAVITATIONAL potential , *DARK matter , *PLANCK'S constant , *FLUCTUATIONS (Physics) - Abstract
The integrated Sachs-Wolfe (ISW) effect measures the decay of the gravitational potential due to cosmic acceleration and is thus a direct probe of dark energy. In some of the earlier studies, the amplitude of the ISW effect was found to be in tension with the predictions of the standard Lambda cold dark matter (ΛCDM) model. We measure the cross power of galaxies and active galactic nuclei (AGN) from the Wide-field Infrared Survey Explorer mission with cosmic microwave background temperature data from WMAP9 in order to provide an independent measurement of the ISW amplitude. Cross-correlations with the recently released Planck lensing potential maps are used to calibrate the bias and contamination fraction of the sources, thus avoiding systematic effects that could be present when using autospectra to measure bias. We find an amplitude of the cross power of A = 1.24±0.47 from the galaxies and A = 0.88±0.74 from the AGN, fully consistent with the ΛCDM prediction of A = 1. The ISW measurement signal-to-noise ratio is 2.7 and 1.2 respectively. Comparing the amplitudes of the Galaxy and AGN cross-correlations, which arise from different redshifts, we find no evidence for redshift evolution in dark energy properties, consistent with a cosmological constant. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
33. A Bayesian neural network predicts the dissolution of compact planetary systems.
- Author
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Cranmer, Miles, Tamayo, Daniel, Rein, Hanno, Battaglia, Peter, Hadden, Samuel, Armitage, Philip J., Ho, Shirley, and Spergel, David N.
- Subjects
- *
PLANETARY systems , *ARTIFICIAL neural networks , *DEEP learning , *MACHINE learning , *MAGNITUDE (Mathematics) - Abstract
We introduce a Bayesian neural network model that can accurately predict not only if, but also when a compact planetary system with three or more planets will go unstable. Our model, trained directly from short N-body time series of raw orbital elements, is more than two orders of magnitude more accurate at predicting instability times than analytical estimators, while also reducing the bias of existing machine learning algorithms by nearly a factor of three. Despite being trained on compact resonant and near-resonant three-planet configurations, the model demonstrates robust generalization to both non resonant and higher multiplicity configurations, in the latter case outperforming models fit to that specific set of integrations. The model computes instability estimates up to 105 times faster than a numerical integrator, and unlike previous efforts provides confidence intervals on its predictions. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
34. Joint likelihood function of cluster counts and n-point correlation functions: Improving their power through including halo sample variance.
- Author
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Schaan, Emmanuel, Masahiro Takada, and Spergel, David N.
- Subjects
- *
SAMPLE variance , *DENSITY , *DARK matter , *PARTICLES (Nuclear physics) , *PARTICLE physics - Abstract
Naive estimates of the statistics of large-scale structure and weak lensing power spectrum measurements that include only Gaussian errors exaggerate their scientific impact. Nonlinear evolution and finite-volume effects are both significant sources of non-Gaussian covariance that reduce the ability of power spectrum measurements to constrain cosmological parameters. Using a halo model formalism, we derive an intuitive understanding of the various contributions to the covariance and show that our analytical treatment agrees with simulations. This approach enables an approximate derivation of a joint likelihood for the cluster number counts, the weak lensing power spectrum and the bispectrum. We show that this likelihood is a good description of the ray-tracing simulation. Since all of these observables are sensitive to the same finite-volume effects and contain information about the nonlinear evolution, a combined analysis recovers much of the "lost" information. For upcoming weak lensing surveys, we estimate that a joint analysis of power spectrum, number counts and bispectrum will produce an improvement of about 30-40% in determinations of the matter density and the scalar amplitude. This improvement is equivalent to doubling the survey area. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
35. The kinetic Sunyaev-Zel'dovich signal from inhomogeneous reionization: a parameter space study.
- Author
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Mesinger, Andrei, McQuinn, Matthew, and Spergel, David N.
- Subjects
- *
COSMIC background radiation , *ANISOTROPY , *INFRARED astronomy , *THERMAL analysis , *ASTRONOMICAL models , *ASTRONOMICAL observations , *SUPERGIANT stars , *ATMOSPHERIC radiation , *PHOTONS - Abstract
ABSTRACT Inhomogeneous reionization acts as a source of arcminute-scale anisotropies in the cosmic microwave background (CMB), the most important of which is the kinetic Sunyaev-Zel'dovich (kSZ) effect. Observational efforts with the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) are poised to detect this signal for the first time, with projected 1 μ K2-level sensitivity to the dimensionless kSZ power spectrum around a multipole of l= 3000, [Δ l3000]2. Indeed, recent SPT measurements place a bound of [Δ l3000 ]2 < 2.8 μ K2 at 95 per cent confidence level, which degrades to [Δ l3000 ]2 < 6 μ K2 if a significant correlation between the thermal Sunyaev-Zel'dovich (tSZ) effect and the cosmic infrared background (CIB) is allowed. To interpret these and upcoming observations, we compute the kSZ signal from a suite of ≈100 reionization models using the publicly available code 21cmfast. Our physically motivated reionization models are parametrized by the ionizing efficiency of high-redshift galaxies, the minimum virial temperature of haloes capable of hosting stars, and the ionizing photon mean free path - a parametrization motivated by previous theoretical studies of reionization. We predict the contribution of patchy reionization to the l= 3000 kSZ power to be 1.5-3.5 μ K2. Therefore, even when adopting the lowest estimate in the literature for the post-reionization signal of , none of our models are consistent with the aggressive 2σ SPT bound that does not include correlations. This implies the following: (i) the early stages of reionization occurred in a much more homogeneous manner than suggested by the stellar-driven scenarios we explore, such as would be the case if, e.g. very high energy X-rays or exotic particles contributed significantly and/or (ii) that there is a significant correlation between the CIB and the tSZ. The later is perhaps not surprising, as massive haloes should host both hot gas and star-forming galaxies. On the other hand, the conservative SPT bound of [Δ l3000 ]2≲ 6 μ K2 is compatible with all of our models and is on the threshold of constraining physically motivated reionization models. The largest patchy kSZ signals correspond to an extended reionization process, in which the sources of ionizing photons are abundant and there are many recombinations (absorptions in sinks). We point out that insights into the astrophysics of the early Universe are encoded in both the amplitude and shape of the kSZ power spectrum. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
36. Using galaxy-galaxy weak lensing measurements to correct the finger of God.
- Author
-
Hikage, Chiaki, Takada, Masahiro, and Spergel, David N.
- Subjects
- *
GALAXIES , *MEASUREMENT , *DISTRIBUTION (Probability theory) , *METAPHYSICAL cosmology , *REDSHIFT , *DARK matter , *IMAGING systems in astronomy , *CALIBRATION - Abstract
ABSTRACT For decades, cosmologists have been using galaxies to trace the large-scale distribution of matter. At present, the largest source of systematic uncertainty in this analysis is the challenge of modelling the complex relationship between galaxy redshift and the distribution of dark matter. If all galaxies sat in the centres of haloes, there would be minimal finger-of-God (FoG) effects and a simple relationship between the galaxy and matter distributions. However, many galaxies, even some of the luminous red galaxies (LRGs), do not lie in the centres of haloes. Because the galaxy-galaxy lensing is also sensitive to the off-centred galaxies, we show that we can use the lensing measurements to determine the amplitude of this effect and to determine the expected amplitude of FoG effects. We develop an approach for using the lensing data to model how the FoG suppresses the power spectrum amplitudes and show that the current data imply a 30 per cent suppression at wavenumber k = 0.2 h Mpc−1. Our analysis implies that it is important to complement a spectroscopic survey with an imaging survey with sufficient depth and wide field coverage. Joint imaging and spectroscopic surveys allow a robust, unbiased use of the power spectrum amplitude information: it improves the marginalized error of growth rate fg≡ d ln D/d ln a by up to a factor of 2 over a wide range of redshifts z < 1.4. We also find that the dark energy equation-of-state parameter, w0, and the neutrino mass, fν, can be unbiasedly constrained by combining the lensing information, with an improvement of 10-25 per cent compared to a spectroscopic survey without lensing calibration. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
37. EVIDENCE AGAINST DARK MATTER HALOS SURROUNDING THE GLOBULAR CLUSTERS MGC1 AND NGC 2419.
- Author
-
CONROY, CHARLIE, LOEB, ABRAHAM, and SPERGEL, DAVID N.
- Subjects
- *
DARK matter , *HALOS (Meteorology) , *STAR clusters , *DENSITY of stars , *STELLAR mass - Abstract
The conjecture that the ancient globular clusters (GCs) formed at the center of their own dark matter (DM) halos was first proposed by Peebles in 1984 and has recently been revived to explain the puzzling abundance patterns observed within many GCs. In this paper, we demonstrate that the outer stellar density profile of isolated GCs is very sensitive to the presence of an extended dark halo. The GCs NGC 2419, located at 90 kpc from the center of our Galaxy, and MGC1, located at ~200 kpc from the center of M31, are ideal laboratories for testing the scenario that GCs formed at the centers of massive dark halos. Comparing analytic models to observations of these GCs, we conclude that these GCs cannot be embedded within dark halos with a virial mass greater than 106 M⊙, or, equivalently, the DM halo-mass-to-stellar mass ratio must be MDM/M* < 1. If these GCs have indeed orbited within weak tidal fields throughout their lifetimes, then these limits imply that these GCs did not form within their own dark halos. Recent observations of an extended stellar halo in the GC NGC 1851 are also interpreted in the context of our analytic models. Implications of these results for the formation of GCs are briefly discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
38. Detecting Neutrino Mass by Combining Matter Clustering, Halos, and Voids.
- Author
-
Bayer, Adrian E., Villaescusa-Navarro, Francisco, Massara, Elena, Liu, Jia, Spergel, David N., Verde, Licia, Wandelt, Benjamin D., Viel, Matteo, and Ho, Shirley
- Subjects
- *
NEUTRINOS , *NEUTRINO mass , *COSMIC background radiation , *N-body simulations (Astronomy) , *CROSS correlation , *POWER spectra , *COVARIANCE matrices - Abstract
We quantify the information content of the nonlinear matter power spectrum, the halo mass function, and the void size function, using the Quijote N-body simulations. We find that these three statistics exhibit very different degeneracies among the cosmological parameters, and thus the combination of all three probes enables the breaking of degeneracies, in turn yielding remarkably tight constraints. We perform a Fisher analysis using the full covariance matrix, including all auto- and cross correlations, finding that this increases the information content for neutrino mass compared to a correlation-free analysis. The multiplicative improvement of the constraints on the cosmological parameters obtained by combining all three probes compared to using the power spectrum alone are: 137, 5, 8, 20, 10, and 43, for Ωm, Ωb, h, ns, σ8, and Mν, respectively. The marginalized error on the sum of the neutrino masses is σ(Mν) = 0.018 eV for a cosmological volume of , using , and without cosmic microwave background (CMB) priors. We note that this error is an underestimate insomuch as we do not consider super-sample covariance, baryonic effects, and realistic survey noises and systematics. On the other hand, it is an overestimate insomuch as our cuts and binning are suboptimal due to restrictions imposed by the simulation resolution. Given upcoming galaxy surveys will observe volumes spanning , this presents a promising new avenue to measure neutrino mass without being restricted by the need for accurate knowledge of the optical depth, which is required for CMB-based measurements. Furthermore, the improved constraints on other cosmological parameters, notably Ωm, may also be competitive with CMB-based measurements. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
39. The CAMELS Project: Cosmology and Astrophysics with Machine-learning Simulations.
- Author
-
Villaescusa-Navarro, Francisco, Anglés-Alcázar, Daniel, Genel, Shy, Spergel, David N., Somerville, Rachel S., Dave, Romeel, Pillepich, Annalisa, Hernquist, Lars, Nelson, Dylan, Torrey, Paul, Narayanan, Desika, Li, Yin, Philcox, Oliver, Torre, Valentina La, Delgado, Ana Maria, Ho, Shirley, Hassan, Sultan, Burkhart, Blakesley, Wadekar, Digvijay, and Battaglia, Nicholas
- Subjects
- *
PHYSICAL cosmology , *GENERATIVE adversarial networks , *ASTROPHYSICS , *CAMELS , *N-body simulations (Astronomy) , *GALACTIC halos - Abstract
We present the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) project. CAMELS is a suite of 4233 cosmological simulations of volume each: 2184 state-of-the-art (magneto)hydrodynamic simulations run with the AREPO and GIZMO codes, employing the same baryonic subgrid physics as the IllustrisTNG and SIMBA simulations, and 2049 N-body simulations. The goal of the CAMELS project is to provide theory predictions for different observables as a function of cosmology and astrophysics, and it is the largest suite of cosmological (magneto)hydrodynamic simulations designed to train machine-learning algorithms. CAMELS contains thousands of different cosmological and astrophysical models by way of varying Ωm, σ8, and four parameters controlling stellar and active galactic nucleus feedback, following the evolution of more than 100 billion particles and fluid elements over a combined volume of. We describe the simulations in detail and characterize the large range of conditions represented in terms of the matter power spectrum, cosmic star formation rate density, galaxy stellar mass function, halo baryon fractions, and several galaxy scaling relations. We show that the IllustrisTNG and SIMBA suites produce roughly similar distributions of galaxy properties over the full parameter space but significantly different halo baryon fractions and baryonic effects on the matter power spectrum. This emphasizes the need for marginalizing over baryonic effects to extract the maximum amount of information from cosmological surveys. We illustrate the unique potential of CAMELS using several machine-learning applications, including nonlinear interpolation, parameter estimation, symbolic regression, data generation with Generative Adversarial Networks, dimensionality reduction, and anomaly detection. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
40. Direct detection of dark matter debris flows.
- Author
-
Kuhlen, Michael, Lisanti, Mariangela, and Spergel, David N.
- Subjects
- *
DARK matter , *PHASE transitions , *PLUMES (Fluid dynamics) , *GALACTIC halos , *COMPUTER simulation , *SPECTRUM analysis - Abstract
Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended "debris flows" in the form of shells, sheets, and plumes. Here we focus on the debris flow in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high velocity behavior. Unlike tidal streams, which may not necessarily intersect the Earth's location, debris flow is spatially uniform at 8 kpc and thus guaranteed to be present in the dark matter flux incident on direct detection experiments. At Earth-frame speeds greater than 450 km/s, debris flow comprises more than half of the dark matter at the Sun's location, and up to 80% at even higher speeds. Therefore, debris flow is most important for experiments that are particularly sensitive to the high speed tail of the dark matter distribution, such as searches for light or inelastic dark matter or experiments with directional sensitivity. We show that debris flow yields a distinctive recoil energy spectrum and a broadening of the distribution of incidence direction. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
41. Predicting the long-term stability of compact multiplanet systems.
- Author
-
Tamayo, Daniel, Cranmer, Miles, Hadden, Samuel, Rein, Hanno, Battaglia, Peter, Obertas, Alysa, Armitage, Philip J., Ho, Shirley, Spergel, David N., Gilbertson, Christian, Hussain, Naireen, Silburt, Ari, Jontof-Hutter, Daniel, and Menou, Kristen
- Subjects
- *
ANGULAR momentum (Mechanics) , *NUMERICAL integration , *VELOCITY measurements , *DISCRETE systems , *DYNAMICAL systems - Abstract
We combine analytical understanding of resonant dynamics in two-planet systems with machine-learning techniques to train a model capable of robustly classifying stability in compact multiplanet systems over long timescales of 109109 orbits. Our Stability of Planetary Orbital Configurations Klassifier (SPOCK) predicts stability using physically motivated summary statistics measured in integrations of the first 104104 orbits, thus achieving speed-ups of up to 105105 over full simulations. This computationally opens up the stability-constrained characterization of multiplanet systems. Our model, trained on ~100,000 three-planet systems sampled at discrete resonances, generalizes both to a sample spanning a continuous period-ratio range, as well as to a large five-planet sample with qualitatively different configurations to our training dataset. Our approach significantly outperforms previous methods based on systems' angular momentum deficit, chaos indicators, and parametrized fits to numerical integrations. We use SPOCK to constrain the free eccentricities between the inner and outer pairs of planets in the Kepler-431 system of three approximately Earth-sized planets to both be below 0.05. Our stability analysis provides significantly stronger eccentricity constraints than currently achievable through either radial velocity or transit-duration measurements for small planets and within a factor of a few of systems that exhibit transit-timing variations (TTVs). Given that current exoplanet-detection strategies now rarely allow for strong TTV constraints [S. Hadden, T. Barclay, M. J. Payne, M. J. Holman, Astrophys. J. 158, 146 (2019)], SPOCK enables a powerful complementary method for precisely characterizing compact multiplanet systems. We publicly release SPOCK for community use. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
42. Limitations to the 'basic' HOD model and beyond.
- Author
-
Hadzhiyska, Boryana, Bose, Sownak, Eisenstein, Daniel, Hernquist, Lars, and Spergel, David N
- Subjects
- *
GALAXY clusters , *GALAXIES - Abstract
We use the IllustrisTNG cosmological, hydrodynamical simulations to test fundamental assumptions of the mass-based halo occupation distribution (HOD) approach to modelling the galaxy–halo connection. By comparing the clustering of galaxies measured in the 300 Mpc TNG box (TNG300) with that predicted by the standard (basic) HOD model, we find that, on average, the 'basic' HOD model underpredicts the real-space correlation function in the TNG300 box by ∼15 per cent on scales of |$1 \,\,\lt\,\, r \,\,\lt\,\, 20 \ {\rm Mpc}\, h^{-1}$| , which is well beyond the target precision demanded of next-generation galaxy redshift surveys. We perform several tests to establish the robustness of our findings to systematic effects, including the effect of finite box size and the choice of halo finder. In our exploration of 'secondary' parameters with which to augment the 'basic' HOD, we find that the local environment of the halo, the velocity dispersion anisotropy, β, and the product of the half-mass radius and the velocity dispersion, σ2 R halfmass, are the three most effective measures of assembly bias that help reconcile the 'basic' HOD-predicted clustering with that in TNG300. In addition, we test other halo properties such as halo spin, formation epoch, and halo concentration. We also find that at fixed halo mass, galaxies in one type of environment cluster differently from galaxies in another. We demonstrate that a more complete model of the galaxy–halo connection can be constructed if we combine both mass and local environment information about the halo. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
43. Massive neutrinos leave fingerprints on cosmic voids.
- Author
-
Kreisch, Christina D, Pisani, Alice, Carbone, Carmelita, Liu, Jia, Hawken, Adam J, Massara, Elena, Spergel, David N, and Wandelt, Benjamin D
- Subjects
- *
NEUTRINOS , *NEUTRINO mass , *DARK matter , *AXIONS , *NEUTRINO interactions - Abstract
Do void statistics contain information beyond the tracer 2-point correlation function? Yes! As we vary the sum of the neutrino masses, we find void statistics contain information absent when using just tracer 2-point statistics. Massive neutrinos uniquely affect cosmic voids. We explore their impact on void clustering using both the DEMNUni and MassiveNuS simulations. For voids, neutrino effects depend on the observed void tracers. As the neutrino mass increases, the number of small voids traced by cold dark matter particles increases and the number of large voids decreases. Surprisingly, when massive, highly biased, haloes are used as tracers, we find the opposite effect. The scale at which voids cluster, as well as the void correlation, is similarly sensitive to the sum of neutrino masses and the tracers. This scale-dependent trend is not due to simulation volume or halo density. The interplay of these signatures in the void abundance and clustering leaves a distinct fingerprint that could be detected with observations and potentially help break degeneracies between different cosmological parameters. This paper paves the way to exploit cosmic voids in future surveys to constrain the mass of neutrinos. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
44. Joint cosmology and mass calibration from thermal Sunyaev-Zel'dovich cluster counts and cosmic shear.
- Author
-
Nicola, Andrina, Dunkley, Jo, and Spergel, David N.
- Subjects
- *
GALAXY clusters , *PHYSICAL cosmology , *DARK energy , *POWER spectra , *CALIBRATION , *COUNTING , *LARGE scale systems - Abstract
We present a new method for joint cosmological parameter inference and cluster mass calibration from a combination of weak lensing measurements and the abundance of thermal Sunyaev-Zel'dovich (tSZ) selected galaxy clusters. We combine cluster counts with the spherical harmonic cosmic shear power spectrum and the cross-correlation between cluster overdensity and cosmic shear. These correlations constrain the cluster mass-observable relation. We model the observables using a halo model framework, including their full non-Gaussian covariance. Forecasting constraints on cosmological and mass calibration parameters for a combination of LSST cosmic shear and Simons Observatory tSZ cluster counts, we find competitive constraints for cluster cosmology, with a factor of 2 improvement in the dark energy figure of merit compared to LSST cosmic shear alone. We find most of the mass calibration information will be in the large and intermediate scales of the cross-correlation between cluster overdensity and cosmic shear. Finally, we find broadly comparable constraints to traditional analyses based on calibrating masses using stacked cluster lensing measurements, with the benefit of consistently accounting for the correlations with cosmic shear. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
45. What does the marked power spectrum measure? Insights from perturbation theory.
- Author
-
Philcox, Oliver H. E., Massara, Elena, and Spergel, David N.
- Subjects
- *
PERTURBATION theory , *POWER spectra , *GRAVITATIONAL effects , *NEUTRINO mass , *POWER tools , *NEUTRINOS - Abstract
The marked power spectrum is capable of placing far tighter constraints on cosmological parameters (particularly the neutrino mass) than the conventional power spectrum. What new information does it contain beyond conventional statistics? Through the development of a perturbative model, we find that the mark induces a significant coupling between non-Gaussianities, which are usually found on small scales, and large scales, leading to the additional information content. The model is derived in the context of one-loop perturbation theory and validated by comparison to N-body simulations across a variety of mark parameters. At moderate redshifts, including for massive neutrino cosmologies, the theory is in good agreement with the simulations. The importance of nonlinear gravitational effects on the large-scale spectra complicates the modeling as there is no well-defined convergence radius of the theory at low z. Extension to higher perturbative order and biased tracers is possible via a similar approach, and a simple model of the latter is shown to yield promising results. The theory becomes nonperturbative at redshift zero for small smoothing scales, with important contributions from higher-order terms: these will need to be studied before the full power of this tool can be realized. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
46. Inner Space/Outer Space (Book).
- Author
-
Spergel, David
- Subjects
- *
METAPHYSICAL cosmology , *NONFICTION - Abstract
Reviews the book 'Inner Space/Outer Space: The Interface Between Cosmology and Particle Physics,' edited by Edward W. Kolb, Michael S. Turner, David Lindley, Keith Olive, David Seckel.
- Published
- 1987
47. Weak lensing of intensity mapping: The cosmic infrared background.
- Author
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Schaan, Emmanuel, Ferraro, Simone, and Spergel, David N.
- Subjects
- *
COSMIC background radiation , *GRAVITATIONAL lenses , *PHOTONS - Abstract
Gravitational lensing deflects the paths of cosmic infrared background (CIB) photons, leaving a measurable imprint on CIB maps. The resulting statistical anisotropy can be used to reconstruct the matter distribution out to the redshifts of CIB sources. To this end, we generalize the cosmic microwave background (CMB) lensing quadratic estimator to any weakly non-Gaussian source field, by deriving the optimal lensing weights. We point out the additional noise and bias caused by the non-Gaussianity and the "self-lensing" of the source field. We propose methods to reduce, subtract, or model these non-Gaussianities. We show that CIB lensing should be detectable with Planck data and detectable at high significance for future CMB experiments like CCAT-Prime. The CIB thus constitutes a new source image for lensing studies, providing constraints on the amplitude of structure at intermediate redshifts between galaxies and the CMB. CIB lensing measurements will also give valuable information on the star-formation history in the Universe, constraining CIB halo models beyond the CIB power spectrum. By laying out a detailed treatment of lens reconstruction from a weakly non-Gaussian source field, this work constitutes a stepping stone toward lens reconstruction from continuum or line intensity mapping data, such as the Lyman-alpha emission, absorption, and the 21 cm radiation. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
48. Taking the Universe's Temperature with Spectral Distortions of the Cosmic Microwave Background.
- Author
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Hill, J. Colin, Battaglia, Nick, Chluba, Jens, Ferraro, Simone, Schaan, Emmanuel, and Spergel, David N.
- Subjects
- *
COSMIC background radiation , *COMPTON scattering , *SUNYAEV-Zel'dovich effect , *ATMOSPHERIC temperature , *SIGNAL-to-noise ratio , *ASTROPHYSICAL radiation - Abstract
The cosmic microwave background (CMB) energy spectrum is a near-perfect blackbody. The standard model of cosmology predicts small spectral distortions to this form, but no such distortion of the skyaveraged CMB spectrum has yet been measured. We calculate the largest expected distortion, which arises from the inverse Compton scattering of CMB photons off hot, free electrons, known as the thermal Sunyaev-Zel'dovich (TSZ) effect. We show that the predicted signal is roughly one order of magnitude below the current bound from the COBE-FIRAS experiment, but it can be detected at enormous significance (> 1 OOOcr) by the proposed Primordial Inflation Explorer (PIXIE). Although cosmic variance reduces the effective signal-to-noise ratio to 230er, this measurement will still yield a subpercent constraint on the total thermal energy of electrons in the observable Universe. Furthermore, we show that PIXIE can detect subtle relativistic effects in the sky-averaged TSZ signal at 30
- Published
- 2015
- Full Text
- View/download PDF
49. IGM CONSTRAINTS FROM THE SDSS-III/BOSS DR9 Lyα FOREST TRANSMISSION PROBABILITY DISTRIBUTION FUNCTION.
- Author
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Lee, Khee-Gan, Hennawi, Joseph F., Spergel, David N., Weinberg, David H., Hogg, David W., Viel, Matteo, Bolton, James S., Bailey, Stephen, Pieri, Matthew M., Carithers, William, Schlegel, David J., Lundgren, Britt, Palanque-Delabrouille, Nathalie, Suzuki, Nao, Schneider, Donald P., and Yèche, Christophe
- Subjects
- *
INTERSTELLAR medium , *ASTROPHYSICS , *QUASARS , *TEMPERATURE , *DENSITY - Abstract
The Lyα forest transmission probability distribution function (PDF) is an established probe of the intergalactic medium (IGM) astrophysics, especially the temperature-density relationship of the IGM. We measure the transmission PDF from 3393 Baryon Oscillations Spectroscopic Survey (BOSS) quasars from Sloan Digital Sky Survey Data Release 9, and compare with mock spectra that include careful modeling of the noise, continuum, and astrophysical uncertainties. The BOSS transmission PDFs, measured at 〈 z〉 = [2.3, 2.6, 3.0], are compared with PDFs created from mock spectra drawn from a suite of hydrodynamical simulations that sample the IGM temperature-density relationship, γ, and temperature at mean density, T0, where T(Δ) = T0Δγ – 1. We find that a significant population of partial Lyman-limit systems (LLSs) with a column-density distribution slope of βpLLS ∼ – 2 are required to explain the data at the low-transmission end of transmission PDF, while uncertainties in the mean Lyα forest transmission affect the high-transmission end. After modeling the LLSs and marginalizing over mean transmission uncertainties, we find that γ = 1.6 best describes the data over our entire redshift range, although constraints on T0 are affected by systematic uncertainties. Within our model framework, isothermal or inverted temperature-density relationships (γ ⩽ 1) are disfavored at a significance of over 4σ, although this could be somewhat weakened by cosmological and astrophysical uncertainties that we did not model. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
50. Subaru weak lensing measurement of a z = 0.81 cluster discovered by the Atacama Cosmology Telescope Survey★.
- Author
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Miyatake, Hironao, Nishizawa, Atsushi J., Takada, Masahiro, Mandelbaum, Rachel, Mineo, Sogo, Aihara, Hiroaki, Spergel, David N., Bickerton, Steven J., Bond, J. Richard, Gralla, Megan, Hajian, Amir, Hilton, Matt, Hincks, Adam D., Hughes, John P., Infante, Leopoldo, Lin, Yen-Ting, Lupton, Robert H., Marriage, Tobias A., Marsden, Danica, and Menanteau, Felipe
- Subjects
- *
STAR clusters , *METAPHYSICAL cosmology , *TELESCOPES , *GRAVITATIONAL lenses , *GALAXY clusters , *ASTRONOMICAL observations , *MEASUREMENT errors - Abstract
We present a Subaru weak lensing measurement of ACT-CL J0022.2−0036, one of the most luminous, high-redshift (z = 0.81) Sunyaev–Zel'dovich (SZ) clusters discovered in the 268 deg2 equatorial region survey of the Atacama Cosmology Telescope that overlaps with Sloan Digital Sky Survey (SDSS) Stripe 82 field. Ours is the first weak lensing study with Subaru at such high redshifts. For the weak lensing analysis using i′-band images, we use a model-fitting (Gauss–Laguerre shapelet) method to measure shapes of galaxy images, where we fit galaxy images in different exposures simultaneously to obtain best-fitting ellipticities taking into account the different point spread functions (PSFs) in each exposure. We also take into account the astrometric distortion effect on galaxy images by performing the model fitting in the world coordinate system. To select background galaxies behind the cluster at z = 0.81, we use photometric redshift estimates for every galaxy derived from the co-added images of multi-passband Br′i′z′Y, with PSF matching/homogenization. After a photometric redshift cut for background galaxy selection, we detect the tangential weak lensing distortion signal with a total signal-to-noise ratio of about 3.7. By fitting a Navarro–Frenk–White model to the measured shear profile, we find the cluster mass to be $M_{200\bar{\rho }_{\rm m}} = [7.5^{+3.2}_{-2.8}({\rm stat.})^{+1.3}_{-0.6}({\rm sys.})]\times 10^{14} \,\mathrm{M}_{\odot }\,h^{-1}$. The weak lensing-derived mass is consistent with previous mass estimates based on the SZ observation, with assumptions of hydrostatic equilibrium and virial theorem, as well as with scaling relations between SZ signal and mass derived from weak lensing, X-ray and velocity dispersion, within the measurement errors. We also show that the existence of ACT-CL J0022.2−0036 at z = 0.81 is consistent with the cluster abundance prediction of the Λ-dominated cold dark matter structure formation model. We thus demonstrate the capability of Subaru-type ground-based images for studying weak lensing of high-redshift clusters. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
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