Yoel Rephaeli

University of California, San Diego, San Diego, California, United States

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Publications (168)587.23 Total impact

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    Yoel Rephaeli · Massimo Persic
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    ABSTRACT: Energy densities of relativistic electrons and protons in extended galactic and intracluster regions are commonly determined from spectral radio and (rarely) $\gamma$-ray measurements. The time-independent particle spectral density distributions are commonly assumed to have a power-law (PL) form over the relevant energy range. A theoretical relation between energy densities of electrons and protons is usually adopted, and energy equipartition is invoked to determine the mean magnetic field strength in the emitting region. We show that for typical conditions, in both star-forming and starburst galaxies, these estimates need to be scaled down substantially due to significant energy losses that (effectively) flatten the electron spectral density distribution, resulting in a much lower energy density than deduced when the distribution is assumed to have a PL form. The steady-state electron distribution in the nuclear regions of starburst galaxies is calculated by accounting for Coulomb, bremsstrahlung, Compton, and synchrotron losses; the corresponding emission spectra of the latter two processes are calculated and compared to the respective PL spectra. We also determine the proton steady-state distribution by taking into account Coulomb and pion production losses, and briefly discuss implications of our steady-state particle spectra for estimates of proton energy densities and magnetic fields.
    Preview · Article · Mar 2015 · The Astrophysical Journal
  • Yoel Rephaeli · Massimo Persic
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    ABSTRACT: Detection of high-energy γ-ray emission from the nearby starburst galaxies M 82 and NGC 253 establishes, for the first time, a direct link between leptonic and hadronic processes in an extragalactic non-AGN environment. We review the most relevant aspects of these processes and contrast theoretical predictions with available radio and γ-ray measurements in order to determine the particle spectral properties and energy densities in these galaxies.
    No preview · Article · Dec 2014 · Nuclear Physics B - Proceedings Supplements
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    Irina Dvorkin · Yoel Rephaeli
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    ABSTRACT: The mass fraction of hot gas in clusters is a basic quantity whose level and dependence on the cluster mass and redshift are intimately linked to all cluster X-ray and Sunyayev–Zel'dovich measures. Modelling the evolution of the gas fraction is clearly a necessary ingredient in the description of the hierarchical growth of clusters through mergers of subclumps and mass accretion on the one hand, and the dispersal of gas from the cluster galaxies by tidal interactions, galactic winds and ram-pressure stripping on the other hand. A reasonably complete description of this evolution can only be given by very detailed hydrodynamical simulations, which are, however, resource-intensive and difficult to implement in the mapping of parameter space. A much more practical approach is the use of semi-analytic modelling that can be easily implemented to explore a wide range of parameters. We present first results from a simple model that describes the build-up of the gas mass fraction in clusters by following the overall impact of the above processes during the merger and accretion history of each cluster in the ensemble. Acceptable ranges for model parameters are deduced through comparison with results of X-ray observations. Basic implications of our work for modelling cluster statistical properties, and the use of these properties in joint cosmological data analyses, are discussed.
    Full-text · Article · Jun 2014 · Monthly Notices of the Royal Astronomical Society
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    Yoel Rephaeli · Meir Shimon
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    ABSTRACT: The expected sensitivity of cluster SZ number counts to neutrino mass in the sub-eV range is assessed. We find that from the ongoing {\it Planck}/SZ measurements the (total) neutrino mass can be determined at a (1-sigma) precision of 0.06 eV, if the mass is in the range 0.1-0.3 eV, and the survey detection limit is set at the 5-sigma significance level. The mass uncertainty is predicted to be lower by a factor ~2/3, if a similar survey is conducted by a cosmic-variance-limited experiment, a level comparable to that projected if CMB lensing extraction is accomplished with the same experiment. At present, the main uncertainty in modeling cluster statistical measures reflects the difficulty in determining the mass function at the high-mass end.
    Preview · Article · Jun 2014
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    ABSTRACT: We show that the fast moving component of the "bullet cluster" (1E0657-56) can induce potentially resolvable redshift differences between multiply-lensed images of background galaxies. The moving cluster effect can be expressed as the scalar product of the lensing deflection angle with the tangential velocity of the mass components, and it is maximal for clusters colliding in the plane of the sky with velocities boosted by their mutual gravity. The bullet cluster is likely to be the best candidate for the first measurement of this effect due to the large collision velocity and because the lensing deflection and the cluster fields can be calculated in advance. We derive the deflection field using multiply-lensed background galaxies detected with the Hubble Space Telescope. The velocity field is modeled using self-consistent N-body/hydrodynamical simulations constrained by the observed X-ray and gravitational lensing features of this system. We predict that the triply-lensed images of systems "G" and "H" straddling the critical curve of the bullet component will show the largest frequency shifts up to ~0.5 km/sec. This is within the range of the Atacama Large Millimeter/sub-millimeter Array (ALMA) for molecular emission, and is near the resolution limit of the new generation high-throughput optical-IR spectrographs. A detection of this effect measures the tangential motion of the subclusters directly, thereby clarifying the tension with LCDM, which is inferred from gas motion less directly. This method may be extended to smaller redshift differences using the Ly-alpha forest towards QSOs lensed by more typical clusters of galaxies. More generally, the tangential component of the peculiar velocities of clusters derived by our method complements the radial component determined by the kinematic SZ effect, providing a full 3-dimensional description of velocities.
    Full-text · Article · Jul 2013 · The Astrophysical Journal
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    Yoel Rephaeli · Massimo Persic
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    ABSTRACT: The detections of high-energy γ-ray emission from the nearby starburst galaxies M 82 & NGC 253, and other local group galaxies, broaden our knowledge of star-driven nonthermal processes and phenomena in non-AGN star-forming galaxies. We review basic aspects of the related processes and their modeling in starburst galaxies. Since these processes involve both energetic electrons and protons accelerated by SN shocks, their respective radiative yields can be used to explore the SN-particle-radiation connection. Specifically, the relation between SN activity, energetic particles, and their radiative yields, is assessed through respective measures of the particle energy density in several star-forming galaxies. The deduced energy densities range from {O}(1{0}^{-1}) eV cm- 3 in very quiet environments to {O}(1{0}2) eV cm- 3 in regions with very high star-formation rates.
    Preview · Article · Apr 2013
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    ABSTRACT: In this paper, we focus on the astrophysical results and the related cosmological implications derived from recent microwave surveys, with emphasis to those coming from the Planck mission. We critically discuss the impact of systematic effects and the role of methods to separate the cosmic microwave background (CMB) signal from the astrophysical emissions and each different astrophysical component from the others. We then review the state-of-the-art diffuse emissions, extragalactic sources, cosmic infrared background and galaxy clusters, addressing the information they provide to our global view of the cosmic structure evolution and for some crucial physical parameters, as the neutrino mass. Finally, we present three different kinds of scientific perspectives for fundamental physics and cosmology offered by the analysis of on-going and future CMB projects at different angular scales dedicated to anisotropies in total intensity and polarization and to absolute temperature.
    Full-text · Article · Mar 2013 · International Journal of Modern Physics D
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    Meir Shimon · Nissan Itzhaki · Yoel Rephaeli
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    ABSTRACT: It is known that modeling uncertainties and astrophysical foregrounds can potentially introduce appreciable bias in the deduced values of cosmological parameters. While it is commonly assumed that these uncertainties will be accounted for to a sufficient level of precision, the level of bias has not been properly quantified in most cases of interest. We show that the requirement that the bias in derived values of cosmological parameters does not surpass nominal statistical error, translates into a maximal level of overall error $O(N^{-1/2})$ on $|\Delta P(k)|/P(k)$ and $|\Delta C_{l}|/C_{l}$, where $P(k)$, $C_{l}$, and $N$ are the matter power spectrum, angular power spectrum, and number of (independent Fourier) modes at a given scale $l$ or $k$ probed by the cosmological survey, respectively. This required level has important consequences on the precision with which cosmological parameters are hoped to be determined by future surveys: In virtually all ongoing and near future surveys $N$ typically falls in the range $10^{6}-10^{9}$, implying that the required overall theoretical modeling and numerical precision is already very high. Future redshifted-21-cm observations, projected to sample $\sim 10^{14}$ modes, will require knowledge of the matter power spectrum to a fantastic $10^{-7}$ precision level. We conclude that realizing the expected potential of future cosmological surveys, which aim at detecting $10^{6}-10^{14}$ modes, sets the formidable challenge of reducing the overall level of uncertainty to $10^{-3}-10^{-7}$.
    Preview · Article · Dec 2012 · Journal of Cosmology and Astroparticle Physics
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    Meir shimon · Sharon Sadeh · Yoel Rephaeli
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    ABSTRACT: Hot gas in filamentary structures induces CMB aniostropy through the SZ effect. Guided by results from N-body simulations, we model the morphology and gas properties of filamentary gas and determine the power spectrum of the anisotropy. Our treatment suggests that power levels can be an appreciable fraction of the cluster contribution at multipoles $\ell\lesssim 1500$. Its spatially irregular morphology and larger characteristic angular scales can help to distinguish this SZ signature from that of clusters. In addition to intrinsic interest in this most extended SZ signal as a probe of filaments, its impact on cosmological parameter estimation should also be assessed. We find that filament `noise' can potentially bias determination of $A_s$, $n_s$, and $w$ (the normalization of the primordial power spectrum, the scalar index, and the dark energy equation of state parameter, respectively) by more than the nominal statistical uncertainty in Planck SZ survey data. More generally, when inferred from future optimal cosmic-variance-limited CMB experiments, we find that virtually all parameters will be biased by more than the nominal statistical uncertainty estimated for these next generation CMB experiments.
    Preview · Article · Sep 2012 · Journal of Cosmology and Astroparticle Physics
  • Massimo Persic · Yoel Rephaeli
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    ABSTRACT: The energy density of cosmic ray protons (CRp) in star-forming environments can be (i) measured from γ-ray πo-decay emission, (ii) inferred from the measured radio non-thermal synchrotron emission (once a theoretical p/e ratio and particle-field equipartition have been assumed), and (iii) estimated from the observed supernova rate and the deduced CRp residency time. For most of the currently available galaxies where these methods can be simultaneously applied, the results of the various methods agree and suggest that CRp energy densities range from 𝒪(10−1) eV cm−3 in very quiet environments up to 𝒪(102) eV cm−3 in very active ones. The only case for which the methods do not agree is the Small Magellanic Cloud, where the discrepancy between measured and estimated CRp energy density may be due to a smaller characteristic CR confinement volume.
    No preview · Article · Mar 2012 · Journal of Physics Conference Series
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    Diego F. Torres · Analia Cillis · Brian Lacki · Yoel Rephaeli
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    ABSTRACT: The common approach to compute the cosmic-ray distribution in an starburst galaxy or region is equivalent to assume that at any point within that environment, there is an accelerator inputing cosmic rays at a reduced rate. This rate should be compatible with the overall volume-average injection, given by the total number of accelerators that were active during the starburst age. These assumptions seem reasonable, especially under the supposition of an homogeneous and isotropic distribution of accelerators. However, in this approach the temporal evolution of the superposed spectrum is not explicitly derived; rather, it is essentially assumed ab-initio. Here, we test the validity of this approach by following the temporal evolution and spatial distribution of the superposed cosmic-ray spectrum and compare our results with those from theoretical models that treat the starburst region as a single source. In the calorimetric limit (with no cosmic-ray advection), homogeneity is reached (typically within 20%) across most of the starburst region. However, values of center-to-edge intensity ratios can amount to a factor of several. Differences between the common homogeneous assumption for the cosmic-ray distribution and our models are larger in the case of two-zone geometries, such as a central nucleus with a surrounding disc. We have also found that the decay of the cosmic-ray density following the duration of the starburst process is slow, and even approximately 1 Myr after the burst ends (for a gas density of 35 cm-3) it may still be within an order of magnitude of its peak value. Based on our simulations, it seems that the detection of a relatively hard spectrum up to the highest gamma-ray energies from nearby starburst galaxies favors a relatively small diffusion coefficient (i.e., long diffusion time) in the region where most of the emission originates.
    Preview · Article · Mar 2012 · Monthly Notices of the Royal Astronomical Society
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    M. Shimon · Y. Rephaeli · N. Itzhaki · I. Dvorkin · B. G. Keating
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    ABSTRACT: Statistical measures of galaxy clusters are sensitive to neutrino masses in the sub-eV range. We explore the possibility of using cluster number counts from the ongoing Planck/SunyaevZel'dovich (SZ) and future cosmic-variance-limited surveys to constrain neutrino masses from cosmic microwave background (CMB) data alone. The precision with which the total neutrino mass can be determined from SZ number counts is limited mostly by uncertainties in the cluster mass function and intracluster gas evolution; these are explicitly accounted for in our analysis. We find that projected results from the Planck/SZ survey can be used to determine the total neutrino mass with a (1σ) uncertainty of 0.06 eV, assuming that it is in the range 0.1 - 0.3 eV, and the survey detection limit is set at the 5σ significance level. Our results constitute a significant improvement on the limits expected from Planck/CMB lensing measurements, 0.15 eV. Based on expected results from the future cosmic-variance-limited (CVL) SZ survey we predict a 1σ uncertainty of 0.04 eV, a level comparable to that expected when CMB lensing extraction is carried out with the same experiment. A few per cent uncertainty in the mass function parameters could result in up to a factor of ∼2–3 degradation of our Planck and CVL forecasts. Our analysis shows that cluster number counts provide a viable complementary cosmological probe to CMB lensing constraints on the total neutrino mass.
    Full-text · Article · Jan 2012 · Monthly Notices of the Royal Astronomical Society
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    Irina Dvorkin · Yoel Rephaeli · Meir Shimon
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    ABSTRACT: We have recently developed an extended merger-tree model that efficiently follows hierarchical evolution of galaxy clusters and provides a quantitative description of both their dark matter and gas properties. We employed this diagnostic tool to calculate the thermal Sunyaev–Zel’dovich power spectrum and cluster number counts, accounting explicitly for uncertainties in the relevant statistical and intrinsic cluster properties, such as the halo mass function and the gas equation of state. Results of these calculations are compared with those obtained from a direct analytic treatment and from hydrodynamical simulations. We show that under certain assumptions on the gas mass fraction our results are consistent with the latest South Pole Telescope measurement. Our approach can be particularly useful in predicting cluster number counts and their dependence on cluster and cosmological parameters.
    Full-text · Article · Jan 2012 · Monthly Notices of the Royal Astronomical Society
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    Massimo Persic · Yoel Rephaeli
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    ABSTRACT: The energy density of cosmic-ray protons (CRp) in star-forming galaxies can be estimated from (i) neutral-pion--decay gamma-ray emission, (ii) synchrotron radio emission, and (iii) supernova rates. For most of the galaxies for which values of all these quantities are known, the three methods yield consistent CRp energy density estimates, ranging from O(0.1) eV/cm3 in galaxies with low star-formation rates, to O(100) eV/cm3 in galaxies with high star-formation rates. The only cases for which the methods do not agree are the composite starburst/Seyfert2 galaxy NGC1068, whose gamma-ray emission originates in black-hole accretion rather than star formation, and the Small Magellanic Cloud, where the discrepancy between measured and estimated CRp energy density may be due to a small CR confinement volume.
    Preview · Article · Jan 2012 · Astronomy and Astrophysics
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    ABSTRACT: Extensive surveys of galaxy clusters motivate us to assess the likelihood of cluster–cluster lensing (CCL), namely, gravitational lensing of a background cluster by a foreground cluster. We briefly describe the characteristics of CCLs in optical, X-ray and Sunyaev–Zel'dovich effect measurements, and calculate their predicted numbers for Λ cold dark matter (ΛCDM) parameters and a viable range of cluster mass functions and their uncertainties. The predicted number of CCLs in the strong-lensing regime varies from several (<10) to as high as a few dozen, depending mainly on whether lensing triaxiality bias is accounted for, through the c–M relation. A much larger number is predicted when taking into account also CCL in the weak-lensing regime. In addition to few previously suggested CCLs, we report a detection of a possible CCL in A383, where background candidate high-z structures are magnified, as seen in deep Subaru observations.
    Full-text · Article · Aug 2011 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We report statistical results for dark matter (DM) velocity anisotropy, β, from a sample of some 6000 cluster-size halos (at redshift zero) identified in a ΛCDM hydrodynamical adaptive mesh refinement simulation performed with the ENZO code. These include profiles of β in clusters with different masses, relaxation states, and at several redshifts, modeled both as spherical and triaxial DM configurations. Specifically, although we find a large scatter in the DM velocity anisotropy profiles of different halos (across elliptical shells extending to at least ~1.5r vir), universal patterns are found when these are averaged over halo mass, redshift, and relaxation stage. These are characterized by a very small velocity anisotropy at the halo center, increasing outward to ~0.27 and leveling off at ~0.2r vir. Indirect measurements of the DM velocity anisotropy fall on the upper end of the theoretically expected range. Though measured indirectly, the estimations are derived by using two different surrogate measurements—X-ray and galaxy dynamics. Current estimates of the DM velocity anisotropy are based on a very small cluster sample. Increasing this sample will allow theoretical predictions to be tested, including the speculation that the decay of DM particles results in a large velocity boost. We also find, in accord with previous works, that halos are triaxial and likely to be more prolate when unrelaxed, whereas relaxed halos are more likely to be oblate. Our analysis does not indicate that there is significant correlation (found in some previous studies) between the radial density slope, γ, and β at large radii, 0.3 r vir < r < r vir.
    Preview · Article · Jun 2011 · The Astrophysical Journal
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    ABSTRACT: We present results from strong lens modelling of 10 000 Sloan Digital Sky Survey (SDSS) clusters, to establish the universal distribution of Einstein radii. Detailed lensing analyses have shown that the inner mass distribution of clusters can be accurately modelled by assuming light traces mass, successfully uncovering large numbers of multiple images. Approximate critical curves and the effective Einstein radius of each cluster can therefore be readily calculated, from the distribution of member galaxies and scaled by their luminosities. We use a subsample of 10 well-studied clusters covered by both SDSS and Hubble Space Telescope (HST) to calibrate and test this method, and show that an accurate determination of the Einstein radius and mass can be achieved by this approach ‘blindly’, in an automated way, and without requiring multiple images as input. We present the results of the first 10 000 clusters analysed in the range 0.1 < z < 0.55 and compare them to theoretical expectations. We find that for this all-sky representative sample the Einstein radius distribution is lognormal in shape, with , , and with higher abundance of large θe clusters than predicted by Λ cold dark matter. We visually inspect each of the clusters with (zs= 2) and find that ∼20 per cent are boosted by various projection effects detailed here, remaining with ∼40 real giant-lens candidates, with a maximum of (zs= 2) for the most massive candidate, in agreement with semi-analytic calculations. The results of this work should be verified further when an extended calibration sample is available.
    Full-text · Article · May 2011 · Monthly Notices of the Royal Astronomical Society
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    Yinon Arieli · Yoel Rephaeli · Michael L. Norman
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    ABSTRACT: Little is known about the origin and basic properties of magnetic fields in clusters of galaxies. High conductivity in magnetized interstellar plasma suggests that galactic magnetic fields are (at least partly) ejected into intracluster (IC) space by the same processes that enrich IC gas with metals. We explore the dispersal of galactic fields by hydrodynamical simulations with our new {\em Enzo-Galcon} code, which is capable of tracking a large number galaxies during cluster assembly, and modeling the processes that disperse their interstellar media. Doing so we are able to describe the evolution of the mean strength of the field and its profile across the cluster. With the known density profile of dispersed gas and an estimated range of coherence scales, we predict the spatial distribution of Faraday rotation measure and find it to be consistent with observational data.
    Preview · Article · Apr 2011 · The Astrophysical Journal
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    ABSTRACT: Clusters of galaxies are uniquely important cosmological probes of the evolution of the large scale structure, whose diagnostic power depends quite significantly on the ability to reliably determine their masses. Clusters are typically modeled as spherical systems whose intracluster gas is in strict hydrostatic equilibrium (i.e., the equilibrium gas pressure is provided entirely by thermal pressure), with the gravitational field dominated by dark matter, assumptions that are only rough approximations. In fact, numerical simulations indicate that galaxy clusters are typically triaxial, rather than spherical, and that turbulent gas motions (induced during hierarchical merger events) provide an appreciable pressure component. Extending our previous work, we present results of a joint analysis of X-ray, weak and strong lensing measurements of Abell 1689. The quality of the data allows us to determine both the triaxial shape of the cluster and the level of non-thermal pressure that is required if the intracluster gas is in hydrostatic equilibrium. We find that the dark matter axis ratios are 1.24 +/- 0.13 and 2.02 +/- 0.01 on the plane of the sky and along the line of sight, respectively, and that about 20% of the pressure is non-thermal. Our treatment demonstrates that the dynamical properties of clusters can be determined in a (mostly) bias-free way, enhancing the use of clusters as more precise cosmological probes.
    Full-text · Article · Mar 2011 · Monthly Notices of the Royal Astronomical Society
  • M. Shimon · S. Sadeh · Y. Rephaeli
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    ABSTRACT: The growth of structure in the Universe begins at the time of radiation–matter equality, which corresponds to energy scales of ∼0.4 eV. All tracers of dark matter evolution are expected to be sensitive to neutrino masses on this and smaller scales. Here we explore the possibility of using cluster number counts and power spectrum obtained from ongoing Sunyaev–Zel’dovich (SZ) surveys to constrain neutrino masses. Specifically, we forecast the capability of ongoing measurements with the Planck satellite and the ground-based South Pole Telescope (SPT) experiment, as well as measurements with the proposed Epic satellite, to set interesting bounds on neutrino masses from their respective SZ surveys. We also consider an Atacama Cosmology Telescope (ACT)-like cosmic microwave background (CMB) experiment that covers only a few hundred deg2 also to explore the trade-off between the survey area and sensitivity and what effect this may have on inferred neutrino masses. We find that for such an experiment a shallow survey is preferable over a deep and low-noise scanning scheme. The precision with which the total neutrino mass can be determined from SZ number counts and power spectrum is limited mostly by uncertainties in the basic cosmological parameters, the mass function of clusters and their mean gas mass fraction; all these are explicitly accounted for in our statistical Fisher matrix treatment. We find that projected results from the Planck SZ survey can, in principle, be used to determine the total neutrino mass with a (1σ) uncertainty of 0.28 eV, if the detection limit of a cluster is set at the 5σ significance level. This is twice as large as the limits expected from Planck CMB lensing measurements. The corresponding limits from the SPT and Epic surveys are ∼0.44 and ∼0.12 eV, respectively. Mapping an area of 200 deg2, ACT measurements are predicted to attain a 1σ uncertainty of 0.61 eV; expanding the observed area to 4000 deg2 will decrease the uncertainty to 0.36 eV.
    No preview · Article · Jan 2011 · Monthly Notices of the Royal Astronomical Society

Publication Stats

3k Citations
587.23 Total Impact Points

Institutions

  • 1988-2015
    • University of California, San Diego
      • Center for Astrophysics and Space Sciences (CASS)
      San Diego, California, United States
  • 1985-2014
    • Tel Aviv University
      • Department of Physics and Astronomy
      Tell Afif, Tel Aviv, Israel
  • 2009
    • Stanford University
      • Department of Physics
      Stanford, CA, United States
  • 1988-2006
    • University of California, Berkeley
      • Department of Physics
      Berkeley, California, United States
  • 2005
    • Scuola Internazionale Superiore di Studi Avanzati di Trieste
      Trst, Friuli Venezia Giulia, Italy
  • 2002
    • California State University, Dominguez Hills
      • Department of Physics
      Carson, California, United States
  • 1992
    • CSU Mentor
      Long Beach, California, United States
  • 1987
    • NASA
      • Goddard Space Flight Centre
      Вашингтон, West Virginia, United States