arXiv subjects

Pengjie Zhang

Publications and source records attributed to Pengjie Zhang.

157 records · Page 9Linked to original sources

arXiv2004

A new method of measuring the peculiar velocity power spectrum

We show that by directly correlating the cluster kinetic Sunyaev Zeldovich (KSZ) flux, the cluster peculiar velocity power spectrum can be measured to $\sim 10%$ accuracy by future large sky coverage KSZ surveys. This method is almost free of systemics entangled in the usual velocity inversion method. The direct correlation brings extra information of density and velocity clustering. We utilize these information to construct two indicators of the Hubble constant and comoving angular distance and propose a novel method to constrain cosmology.

astro-ph↗

arXiv2004

Angular Correlations of the MeV Cosmic Gamma Ray Background

The measured cosmic gamma ray background (CGB) spectrum at MeV energies is in reasonable agreement with the predicted contribution from type Ia supernovae (SNIa). But the characteristic features in the SNIa gamma ray spectrum, weakened by integration over source redshifts, are hard to measure, and additionally the contributions from other sources in the MeV range are uncertain, so that the SNIa origin of the MeV CGB remains unproven. Since different CGB sources have different clustering properties and redshift distributions, by combining the CGB spectrum and angular correlation measurements, the contributions to the CGB could be identified and separated. The SNIa CGB large-scale structure follows that of galaxies. Its rms fluctuation at degree scales has a characteristic energy dependence, ranging from $\sim 1%$ to order of unity and can be measured to several percent precision by proposed future satellites such as the Advanced Compton Telescope. With the identification of the SNIa contribution, the SNIa rate could be measured unambiguously as a function of redshift up to $z \sim 1$, by combining both the spectrum and angular correlation measurements, yielding new constraints on the star formation rate to even higher redshifts. Finally, we show that the gamma ray and neutrino backgrounds from supernovae should be closely connected, allowing an important consistency test from the measured data. Identification of the astrophysical contributions to the CGB would allow much greater sensitivity to an isotropic high-redshift CGB contribution arising in extra dimension or dark matter models.

astro-ph↗

arXiv2004

The intergalactic medium temperature and Compton y parameter

(Abridged) The precision modeling of the thermal Sunyaev Zeldovich (SZ) effect and future high accuracy measurements will provide a powerful way to constrain the thermal history of the universe. In this paper, we combine high resolution adiabatic hydro simulations and analytical models to provide a precision modeling of the gas density weighted temperature $\bar{T}_g$ and the mean SZ Compton $y$ parameter. Simulation artifacts are quantified and corrected and our analytical model passes tests of various simulations and is able to predict $\bar{T}_g$ and $\bar{y}$ to several percent accuracy. For low matter density $Λ$CDM cosmology, the present $\bar{T}_g$ is $0.32 (σ_8/0.84)^{3.05-0.15Ω_m}(Ω_m/0.268)^{1.28-0.2σ_8} {\rm keV}$. The mean $y$ parameter is $2.6\times 10^{-6} (σ_8/0.84)^{4.1-2Ω_m}(Ω_m/0.268)^{1.28-0.2σ_8}$. The current upper limit of $y<1.5\times 10^{-5}$ measured by FIRAS has already ruled out combinations of high $σ_8\ga 1.1$ and high $Ω_m\ga 0.5$.

astro-ph↗

arXiv2004

Cross correlations of the cosmic infrared background

The cosmic infrared background (CIB) is a sensitive measure of the star formation history. But this background is overwhelmed by foregrounds, which bias the CIB mean flux and auto correlation measurement severely. Since dominant foregrounds do not correlate with the large scale structure, the cross correlation of CIB with galaxies is free of such foregrounds and presents as an unbiased measure of the star formation history. This also allows the measurement of CIB based on integrated intensity, whose theoretical prediction is based on energy conservation, thus is fairly model independent and robust. The redshift information of CIB sources can be directly recovered with the aid of galaxy photometric redshifts. In the far IR region, correlation signal is around 10% at degree scale. Combining FIRAS and SDSS, the cross correlation can be measured with 20% accuracy (statistical and systematics errors) at $l\sim 40$. Such measurement would allow the measurement of star formation rate with comparable accuracies to $z\sim 1$. Future CIB experiments with $1^{\circ}$ resolution are able to measure the star formation rate with 10% accuracy to $z\sim 1.5$. Secondary CMB anisotropies arising from the large scale structure correlate with CIB. The correlation strength is about $0.5μ$K at $\sim 10^{\circ}$ (the integrated Sachs-Wolfe effect) and $\sim -0.3μ$K at $\sim 1^{\circ}$ (the Sunyaev Zeldovich effect, Rayleigh-Jeans regime). FIRAS+WMAP would allow the measurement of the ISW effect with $\ga 5σ$ confidence. Its detection helps to constrain the amount of dark energy and far IR emissivity bias.

astro-ph↗

arXiv2003

The effect of cluster magnetic field on the Sunyaev Zeldovich power spectrum

Precision measurements of the Sunyaev Zeldovich (SZ) effect in upcoming blank sky surveys require theoretical understanding of all physical processes with $\ga 10%$ effects on the SZ power spectrum. We show that, observed cluster magnetic field could reduce the SZ power spectrum by $\sim 20%$ at $l\sim 4000$, where the SZ power spectrum will be precisely measured by the Sunyaev Zeldovich array (SZA) and the Atacama cosmology telescope (ACT). At smaller scale, this effect is larger and could reach a factor of several. Such effect must be considered for an unbiased interpretation of the SZ data. Though the magnetic effect on the SZ power spectrum is very similar to that of radiative cooling, it is measurable by multi-band CMB polarization measurement.

astro-ph↗

arXiv2003

Precision era of the kinetic Sunyaev-Zeldovich effect: simulations, analytical models and observations and the power to constrain reionization

The kinetic SZ effect, which is the dominant CMB source at arc-minute scales and $ν\sim 217$ Ghz, probes the ionized gas peculiar momentum up to the epoch of reionization and is a sensitive measure of the reionization history. We ran high resolution self-similar and $Λ$CDM hydro simulations and built an analytical model to study this effect. Our model reproduces the $Λ$CDM simulation results to several percent accuracy, passes various tests against self-similar simulations, and shows a wider range of applicability than previous analytical models. Our model in its continuous version is free of simulation limitations such as finite simulation box and finite resolution and allows an accurate prediction of the kinetic SZ power spectrum $C_l$. For the WMAP cosmology, we find $l^2C_l/(2π)\simeq 0.91 \times 10^{-12} [(1+z_{\rm reion})/10]^{0.34}(l/5000)^{0.23-0.015(z_{\rm reion}-9)}$ for the reionization redshift $6<z_{\rm reion}<20$ and $3000<l<9000$. The corresponding temperature fluctuation is several $μ$K at these ranges. The dependence of $C_l$ on the reionization history allows an accurate measurement of the reionization epoch. For the Atacama cosmology telescope experiment, $C_l$ can be measured with $\sim 1%$ accuracy. $C_l$ scales as $(Ω_b h)^2 σ_8^{4\sim 6}$. Given cosmological parameters, ACT would be able to constrain $z_{\rm reion}$ with several percent accuracy. Some multi-reionization scenarios degenerate in the primary CMB temperature and TE measurement can be distinguished with $\sim 10 σ$ confidence.

astro-ph↗

arXiv2003

Optimal Weak Lensing Skewness Measurements

Weak lensing measurements are entering a precision era to statistically map the distribution of matter in the universe. The most common measurement has been of the variance of the projected surface density of matter, which corresponds to the induced correlation in alignments of background galaxies. This measurement of the fluctuations is insensitive to the total mass content, like using waves on the ocean to measure its depths. But when the depth is shallow as happens near a beach, waves become skewed. Similarly, a measurement of skewness in the projected matter distribution directly measures the total matter content of the universe. While skewness has already been convincingly detected, its constraint on cosmology is still weak. We address optimal analyses for the CFHT Legacy Survey in the presence of noise. We show that a compensated Gaussian filter with a width of 2.5 arc minutes optimizes the cosmological constraint, yielding $ΔΩ_m/Ω_m\sim 10%$. This is significantly better than other filters which have been considered in the literature. This can be further improved with tomography and other sophisticated analyses.

astro-ph↗

arXiv2003

Detection of dark matter Skewness in the VIRMOS-DESCART survey: Implications for Ω_0

Weak gravitational lensing provides a direct statistical measure of the dark matter distribution. The variance is easiest to measure, which constrains the degenerate product σ_8Ω^0.6. The degeneracy is broken by measuring the skewness arising from the fact that densities must remain positive, which is not possible when the initially symmetric perturbations become non-linear. Skewness measures the non-linear mass scale, which in combination with the variance measures Ωdirectly. We present the first detection of dark matter skewness from the Virmos-Decart survey. We have measured the full three point function, and its projections onto windowed skewness. We separate the lensing mode and the B mode. The lensing skewness is detected for a compensated Gaussian on scales of 5.37 arc minutes to be κ^3=1.06+/-0.06x10^-6. The B-modes are consistent with zero at this scale. The variance for the same window function is κ^2= 5.32+/-0.62+/-0.98x10^-5, resulting in S_3=375^{+342}_{-124}. Comparing to N-body simulations, we find Ω_0<0.5 at 90% confidence. The Canada-France-Hawaii-Telescope legacy survey and newer simulations should be able to improve significantly on the constraint.

astro-ph↗

arXiv2003

Measuring Feedback Using the Intergalactic Medium State and Evolution Inferred from the Soft X-ray Background

We explore the intergalactic medium (IGM) as a potential source of the unresolved soft X-ray background (XRB) and the feasibility to extract the IGM state and evolution from XRB observations. We build two analytical models, the continuum field model and the halo model, to calculate the IGM XRB mean flux, angular auto correlation and cross correlation with galaxies. Our results suggest that the IGM may contribute a significant fraction to the unresolved soft XRB flux and correlations. We calibrated non-Gaussian errors estimated against our $512^3$ moving mesh hydro simulation and estimate that the ROSAT all sky survey plus Sloan galaxy photometric redshift survey would allow a $\sim 10%$ accuracy in the IGM XRB-galaxy cross correlation power spectrum measurement for $800<l<5000$ and a $\sim 20%$ accuracy in the redshift resolved X-ray emissivity-galaxy cross correlation power spectrum measurement for $z\lesssim 0.5$. At small scales, non-gravitational heating, e.g. feedback, dominates over gravity and leaves unique signatures in the IGM XRB, which allows a comparable accuracy in the measurement of the amount of non-gravitational heating and the length scales where non-gravitational energy balances gravity.

astro-ph↗

arXiv2002

Hydrodynamical Simulations of the IGM at High Mach Numbers

We present a new approach to doing Eulerian computational fluid dynamics that is designed to work at high Mach numbers encountered in hydrodynamical simulations of the IGM. In conventional Eulerian CFD, the thermal energy is poorly tracked in supersonic bulk flows where local fluid variables cannot be accurately separated from the much larger bulk flow components. We described a method in which local fluid quantities can be directly tracked and the Eulerian fluid equations solved in a local frame moving with the flow. The new algorithm has been used to run large hydrodynamical simulations on a 1024^3 grid to study the kinetic SZ effect. The KSZ power spectrum is broadly peaked at l~10^4 with temperature fluctuations on micro Kelvin levels.

astro-ph↗

arXiv2002

The Sunyaev Zel'dovich effect: simulation and observation

The Sunyaev Zel'dovich effect (SZ effect) is a complete probe of ionized baryons, the majority of which are likely hiding in the intergalactic medium. We ran a $512^3$ $Λ$CDM simulation using a moving mesh hydro code to compute the statistics of the thermal and kinetic SZ effect such as the power spectra and measures of non-Gaussianity. The thermal SZ power spectrum has a very broad peak at multipole $l\sim 2000-10^4$ with temperature fluctuations $ΔT \sim 15μ$K. The power spectrum is consistent with available observations and suggests a high $σ_8\simeq 1.0$ and a possible role of non-gravitational heating. The non-Gaussianity is significant and increases the cosmic variance of the power spectrum by a factor of $\sim 5$ for $l<6000$. We explore optimal driftscan survey strategies for the AMIBA CMB interferometer and their dependence on cosmology. For SZ power spectrum estimation, we find that the optimal sky coverage for a 1000 hours of integration time is several hundred square degrees. One achieves an accuracy better than 40% in the SZ measurement of power spectrum and an accuracy better than 20% in the cross correlation with Sloan galaxies for $2000<l<5000$. For cluster searches, the optimal scan rate is around 280 hours per square degree with a cluster detection rate 1 every 7 hours, allowing for a false positive rate of 20% and better than 30% accuracy in the cluster SZ distribution function measurement.

astro-ph↗

arXiv2001

Friedmann Equation and Stability of Inflationary Higher Derivative Gravity

Stability analysis on the De Sitter universe in pure gravity theory is known to be useful in many aspects. We first show how to complete the proof of an earlier argument based on a redundant field equation. It is shown further that the stability condition applies to $k \ne 0$ Friedmann-Robertson-Walker spaces based on the non-redundant Friedmann equation derived from a simple effective Lagrangian. We show how to derive this expression for the Friedmann equation of pure gravity theory. This expression is also generalized to include scalar field interactions.

gr-qc↗

arXiv2000

Deprojecting Sunyaev-Zeldovich statistics

We apply the hierarchical clustering model and non-linear perturbation theory to the cosmological density and temperature fields. This allows us to calculate the intergalactic gas pressure power spectrum, SZ anisotropy power spectrum, skewness and related statistics. Then we show the effect of the non-gravitational heating. Our model confirms recent simulations yielding mass weighted gas temperature \bar{T}_g \sim 0.35 keV and reproduces the power spectra found in these simulations. While the SZ effect contains only angular information, we show that it is possible to extract the full time resolved gas pressure power spectrum when combined with galaxy photometric redshift surveys by using a variation on the cross-correlation. This method further allows the disentanglement of the gravitational and the non-gravitational heating.

astro-ph↗