Publications (109)382.39 Total impact

Article: Tangential Velocity of the Dark Matter in the Bullet Cluster from Precise Lensed Image Redshifts
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ABSTRACT: We show that the fast moving component of the "bullet cluster" (1E065756) can induce potentially resolvable redshift differences between multiplylensed 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 multiplylensed background galaxies detected with the Hubble Space Telescope. The velocity field is modeled using selfconsistent Nbody/hydrodynamical simulations constrained by the observed Xray and gravitational lensing features of this system. We predict that the triplylensed 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/submillimeter Array (ALMA) for molecular emission, and is near the resolution limit of the new generation highthroughput opticalIR 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 Lyalpha 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 3dimensional description of velocities.The Astrophysical Journal 07/2013; 774(1). · 6.73 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: The detections of highenergy γray emission from the nearby starburst galaxies M 82 & NGC 253, and other local group galaxies, broaden our knowledge of stardriven nonthermal processes and phenomena in nonAGN starforming 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 SNparticleradiation 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 starforming 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 starformation rates.01/2013;  [show abstract] [hide abstract]
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 redshifted21cm 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 $10^{3}10^{7}$.Journal of Cosmology and Astroparticle Physics 12/2012; 2013(03). · 6.04 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: Hot gas in filamentary structures induces CMB aniostropy through the SZ effect. Guided by results from Nbody 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 cosmicvariancelimited 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.Journal of Cosmology and Astroparticle Physics 09/2012; 2012(10). · 6.04 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: Statistical measures of galaxy clusters are sensitive to neutrino masses in the subeV range. We explore the possibility of using cluster number counts from the ongoing PLANCK/SZ and future cosmicvariancelimited surveys to constrain neutrino masses from 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 (1\sigma) uncertainty of 0.06 eV, assuming it is in the range 0.10.3 eV, and the survey detection limit is set at the 5\sigma 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 future cosmicvariancelimited (CVL) SZ survey we predict a 1\sigma uncertainty of 0.04 eV, a level comparable to that expected when CMB lensing extraction is carried out with the same experiment. A few percent uncertainty in the mass function parameters could result in up to a factor \sim 23 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.Monthly Notices of the Royal Astronomical Society 01/2012; 427(1). · 5.52 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We have recently developed an extended mergertree 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 SZ 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 SPT measurement. Our approach can be particularly useful in predicting cluster number counts and their dependence on cluster and cosmological parameters.Monthly Notices of the Royal Astronomical Society 01/2012; 421(3). · 5.52 Impact Factor 
Article: Cosmic rays in starforming galaxies
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ABSTRACT: The energy density of cosmic ray protons (CRp) in starforming environments can be (i) measured from γray πodecay emission, (ii) inferred from the measured radio nonthermal synchrotron emission (once a theoretical p/e ratio and particlefield 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.Journal of Physics Conference Series 01/2012; 355(1).  [show abstract] [hide abstract]
ABSTRACT: The energy density of cosmicray protons (CRp) in starforming galaxies can be estimated from (i) neutralpiondecay gammaray 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 starformation rates, to O(100) eV/cm3 in galaxies with high starformation rates. The only cases for which the methods do not agree are the composite starburst/Seyfert2 galaxy NGC1068, whose gammaray emission originates in blackhole 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.01/2012;  [show abstract] [hide abstract]
ABSTRACT: Extensive surveys of galaxy clusters motivate us to assess the likelihood of clustercluster lensing (CCL), namely, gravitationallensing of a background cluster by a foreground cluster. We briefly describe the characteristics of CCLs in optical, Xray and SZ measurements, and calculate their predicted numbers for $\Lambda$CDM parameters and a viable range of cluster mass functions and their uncertainties. The predicted number of CCLs in the stronglensing regime varies from several ($<10$) to as high as a few dozen, depending mainly on whether lensing triaxiality bias is accounted for, through the cM relation. A much larger number is predicted when taking into account also CCL in the weaklensing 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.Monthly Notices of the Royal Astronomical Society 08/2011; 420(2). · 5.52 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We report statistical results for dark matter (DM) velocity anisotropy, \beta, from a sample of some 6000 clustersize halos (at redshift zero) identified in a \Lambda CDM hydrodynamical adaptive mesh refinement simulation performed with the Enzo code. These include profiles of \beta\ 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 ~$1.5 r_{vir}$), 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 about 0.27 and leveling off at about $0.2 r_{vir}$. 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  Xray and galaxy dynamics. Current estimates of the DM velocity anisotropy are based on very small cluster sample. Increasing this sample will allow testing theoretical predictions, 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, \gamma, and \beta\ at large radii, $0.3 r_{vir} < r < r_{vir}$.The Astrophysical Journal 06/2011; 752(2). · 6.73 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We present results from stronglens modelling of 10,000 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 multipleimages. 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 wellstudied clusters covered by both SDSS and 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 allsky representative sample the Einstein radius distribution is lognormal in shape, with $< Log(\theta_{e}\arcsec)>=0.73^{+0.02}_{0.03}$, $\sigma=0.316^{+0.004}_{0.002}$, and with higher abundance of large $\theta_{e}$ clusters than predicted by $\Lambda$CDM. We visually inspect each of the clusters with $\theta_{e}>40 \arcsec$ ($z_{s}=2$) and find that $\sim20%$ are boosted by various projection effects detailed here, remaining with $\sim40$ real giantlens candidates, with a maximum of $\theta_{e}=69\pm12 \arcsec$ ($z_{s}=2$) for the most massive candidate, in agreement with semianalytic calculations. The results of this work should be verified further when an extended calibration sample is available.Monthly Notices of the Royal Astronomical Society 05/2011; · 5.52 Impact Factor  [show abstract] [hide abstract]
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 EnzoGalcon} 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.The Astrophysical Journal 04/2011; 738. · 6.73 Impact Factor  [show abstract] [hide abstract]
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 Xray, 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 nonthermal 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 nonthermal. Our treatment demonstrates that the dynamical properties of clusters can be determined in a (mostly) biasfree way, enhancing the use of clusters as more precise cosmological probes.Monthly Notices of the Royal Astronomical Society 03/2011; 416. · 5.52 Impact Factor  [show abstract] [hide abstract]
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 groundbased 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 tradeoff 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 lownoise 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.Monthly Notices of the Royal Astronomical Society 01/2011; 412(3):1895  1904. · 5.52 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: Adopting the convectiondiffusion model for energetic electron and proton propagation, and accounting for all the relevant hadronic and leptonic processes, the steadystate energy distributions of these particles in the starburst galaxies M82 and NGC253 can be determined with a detailed numerical treatment. The electron distribution is directly normalized by the measured synchrotron radio emission from the central starburst region; a commonly expected theoretical relation is then used to normalize the proton spectrum in this region, and a radial profile is assumed for the magnetic field. The resulting radiative yields of electrons and protons are calculated: the predicted >100MeV and >100GeV fluxes are in agreement with the corresponding quantities measured with the orbiting Fermi telescope and the groundbased VERITAS and HESS Cherenkov telescopes. The cosmicray energy densities in central regions of starburst galaxies, as inferred from the radio and gammaray measurements of (respectively) nonthermal synchrotron and neutralpiondecay emission, are U=O(100) eV/cm3, i.e. at least an order of magnitude larger than near the Galactic center and in other nonveryactively starforming galaxies. These very different energy density levels reflect a similar disparity in the respective supernova rates in the two environments. A L(gamma) ~ SFR^(1.4) relationship is then predicted, in agreement with preliminary observational evidence.01/2011;  [show abstract] [hide abstract]
ABSTRACT: We use extensive measurements of the cluster A1689 to assess the expected similarity in the dynamics of galaxies and dark matter (DM) in their motion as collisionless "particles" in the cluster gravitational potential. To do so, we derive the radial profile of the specific kinetic energy of the cluster galaxies from the Jeans equation and observational data. Assuming that the specific kinetic energies of galaxies and DM are roughly equal, we obtain the mean value of the DM velocity anisotropy parameter and the DM density profile. Since this deduced profile has a scale radius that is higher than inferred from lensing observations, we tested the validity of the assumption by repeating the analysis using results of simulations for the profile of the DM velocity anisotropy. Results of both analyses indicate a significant difference between the kinematics of galaxies and DM within r 0.3r vir. This finding is also reflected in the shape of the galaxy number density profile, which flattens markedly with respect to the steadily rising DM profile at small radii. Thus, r ~ 0.3r vir seems to be a transition region interior to which collisional effects significantly modify the dynamical properties of the galaxy population with respect to those of DM in A1689.The Astrophysical Journal 01/2011; 728(1):40. · 6.73 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We model the formation and evolution of galaxy clusters in the framework of an extended dark matter halo mergertree algorithm that includes baryons and incorporates basic physical considerations. Our modified treatment is employed to calculate the probability density functions of the halo concentration parameter, intracluster gas temperature, and the integrated Comptonization parameter for different cluster masses and observation redshifts. Scaling relations between cluster mass and these observables are deduced that are somewhat different than previous results. Modeling uncertainties in the predicted probability density functions are estimated. Our treatment and the insight gained from the results presented in this paper can simplify the comparison of theoretical predictions with results from ongoing and future cluster surveys.Monthly Notices of the Royal Astronomical Society 10/2010; 412. · 5.52 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: The growth of structure in the universe begins at the time of radiationmatter equality, which corresponds to energy scales of $\sim 0.4 eV$. 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 SZ surveys to constrain neutrino masses. Specifically, we forecast the capability of ongoing measurements with the PLANCK satellite and the groundbased 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 ACTlike CMB experiment that covers only a few hundred ${\rm deg^{2}}$ also to explore the tradeoff 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 lownoise scanning scheme. We also find that projected results from the PLANCK SZ survey can, in principle, be used to determine the total neutrino mass with a ($1\sigma$) uncertainty of $0.28 eV$, if the detection limit of a cluster is set at the $5\sigma$ 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 $\sim 0.44 eV$ and $\sim 0.12 eV$, respectively. Mapping an area of 200 deg$^{2}$, ACT measurements are predicted to attain a $1\sigma$ uncertainty of 0.61 eV; expanding the observed area to 4,000 deg$^{2}$ will decrease the uncertainty to 0.36 eV. Comment: 14 pages, 1 figure, 6 tables09/2010;  [show abstract] [hide abstract]
ABSTRACT: We present a stronglensing analysis of the galaxy cluster MS 1358.4+6245 ($z=0.33$), in deep 6band ACS/HST imaging. In addition to the wellstudied system at $z=4.92$, our modelling method uncovers 19 new multiplylensed images so that a total of 23 images and their redshifts are used to accurately constrain the inner mass distribution. We derive a relatively shallow inner mass profile, $d\log \Sigma/d\log r\simeq 0.33 \pm0.05$ ($r<200$ kpc), with a much higher magnification than estimated previously by models constrained only by the $z=4.92$ system. Using these many new images we can apply a nonparametric adaptivegrid method, which also yields a shallow mass profile without prior assumptions, strengthening our conclusions. The total magnification of the $z_s=4.92$ galaxy is high, about a $\sim100\times$ over its four images, so that the inferred source size, luminosity and starformation rate are about $\sim5\times$ smaller than previous estimates, corresponding to a dwarfsized galaxy of radius $\simeq1$ kpc. A detailed image of the interior morphology of the source is generated with a high effective resolution of only $\simeq$50 pc, thanks to the high magnification and to the declining angular diameter distance above $z\sim1.5$ for the standard cosmology, so that this image apparently represents the best resolved object known at high redshift.Monthly Notices of the Royal Astronomical Society 09/2010; · 5.52 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: The inner massprofile of the relaxed cluster Abell 1703 is analysed by two very different stronglensing techniques applied to deep ACS and WFC3 imaging. Our parametric method has the accuracy required to reproduce the many sets of multiple images, based on the assumption that mass approximately traces light. We test this assumption with a fully nonparametric, adaptive grid method, with no knowledge of the galaxy distribution. Differences between the methods are seen on fine scales due to member galaxies which must be included in models designed to search for lensed images, but on the larger scale the general distribution of dark matter is in good agreement, with very similar radial mass profiles. We add undiluted weaklensing measurements from deep multicolour Subaru imaging to obtain a fully modelindependent mass profile out to the virial radius and beyond. Consistency is found in the region of overlap between the weak and strong lensing, and the full mass profile is welldescribed by an NFW model of a concentration parameter, $c_{\rm vir}\simeq 7.15\pm0.5$ (and $M_{vir}\simeq 1.22\pm0.15 \times 10^{15}M_{\odot}/h$). Abell 1703 lies above the standard $c$$M$ relation predicted for the standard $\Lambda$CDM model, similar to other massive relaxed clusters with accurately determined lensingbased profiles.Monthly Notices of the Royal Astronomical Society 04/2010; 408. · 5.52 Impact Factor
Publication Stats
474  Citations  
382.39  Total Impact Points  
Top Journals
Institutions

2013

Ikerbasque  Basque Foundation for Science
Bilbo, Basque Country, Spain


1999–2012

Tel Aviv University
 Department of Physics and Astronomy
Tell Afif, Tel Aviv, Israel


2006–2011

University of California, San Diego
 Center for Astrophysics and Space Sciences (CASS)
San Diego, California, United States 
University of California, Berkeley
Berkeley, California, United States


2009

Stanford University
Palo Alto, California, United States


2002

California State University, Dominguez Hills
 Department of Physics
Carson, California, United States
