54 research outputs found
Detecting z > 10 objects through carbon, nitrogen and oxygen emission lines
By redshift of 10, star formation in the first objects should have produced
considerable amounts of Carbon, Nitrogen and Oxygen. The submillimeter lines of
C, N and O redshift into the millimeter and centimeter bands (0.5 mm -- 1.2
cm), where they may be detectable. High spectral resolution observations could
potentially detect inhomogeneities in C, N and O emission, and see the first
objects forming at high redshift. We calculate expected intensity fluctuations
and discuss frequency and angular resolution required to detect them. For CII
emission, we estimate the intensity using two independent methods: the line
emission coefficient argument and the luminosity density argument. We find they
are in good agreement. At 1+z \sim 10, the typical protogalaxy has a velocity
dispersion of 30 km s^{-1} and angular size of 1 arcsecond. If CII is the
dominant coolant, then we estimate a characteristic line strength of \sim 0.1 K
km s^{-1}. We also discuss other atomic lines and estimate their signal.
Observations with angular resolution of 10^{-3} can detect moderately nonlinear
fluctuations of amplitude 2 \cdot 10^{-5} times the microwave background. If
the intensity fluctuations are detected, they will probe matter density
inhomogeneity, chemical evolution and ionization history at high redshifts.Comment: 15 pages, 1 postscript figures included; Uses aaspp4.sty (AASTeX
v4.0); Submitted to The Astrophysical Journa
Cross-Correlating Cosmic Microwave Background Radiation Fluctuations with Redshift Surveys: Detecting the Signature of Gravitational Lensing
Density inhomogeneities along the line-of-sight distort fluctuations in the
cosmic microwave background. Usually, this effect is thought of as a small
second-order effect that mildly alters the statistics of the microwave
background fluctuations. We show that there is a first-order effect that is
potentially observable if we combine microwave background maps with large
redshift surveys. We introduce a new quantity that measures this lensing
effect, , where T is the microwave
background temperature and is the lensing due to matter in the
region probed by the redshift survey. We show that the expected signal is first
order in the gravitational lensing bending angle, , and find that it should be easily detectable, (S/N) 15-35, if
we combine the Microwave Anisotropy Probe satellite and Sloan Digital Sky
Survey data. Measurements of this cross-correlation will directly probe the
``bias'' factor, the relationship between fluctuations in mass and fluctuations
in galaxy counts.Comment: 13 pages, 4 postscript figures included; Uses aaspp4.sty (AASTeX
v4.0); Accepted for publication in Astrophysical Journal, Part
The Effect of Cooling on the Density Profile of Hot Gas in Clusters of Galaxies: Is Additional Physics Needed?
We use high-resolution hydrodynamic simulations to investigate the density
profile of hot gas in clusters of galaxies, adopting a variant of cold dark
matter cosmologies and employing a cosmological N-body/smoothed particle
hydrodynamics code to follow the evolution of dark matter and gas. In addition
to gravitational interactions, gas pressure, and shock heating, we include
bremsstrahlung cooling in the computation. Dynamical time, two-body relaxation
time, and cooling time in the simulations are examined to demonstrate that the
results are free from artificial relaxation effects and that the time step is
short enough to accurately follow the evolution of the system. In the
simulation with nominal resolution of 66h^{-1} kpc the computed cluster appears
normal, but in a higher (by a factor 2) resolution run, cooling is so efficient
that the final gas density profile shows a steep rise toward the cluster center
that is not observed in real clusters. Also, the X-ray luminosity of
7\times10^{45} ergs s^{-1} far exceeds that for any cluster of the computed
temperature. The most reasonable explanation for this discrepancy is that there
are some physical processes still missing in the simulations that actually
mitigate the cooling effect and play a crucial role in the thermal and
dynamical evolution of the gas near the center. Among the promising candidate
processes are heat conduction and heat input from supernovae. We discuss the
extent to which these processes can alter the evolution of gas.Comment: 19 pages, 5 postscript figures included; uses aaspp4.sty (AASTeX
v4.0); title changed; final version published in The Astrophysical Journa
Reconstructing Projected Matter Density from Cosmic Microwave Background
Gravitational lensing distorts the cosmic microwave background (CMB)
anisotropies and imprints a characteristic pattern onto it. The distortions
depend on the projected matter density between today and redshift . In this paper we develop a method for a direct reconstruction of the
projected matter density from the CMB anisotropies. This reconstruction is
obtained by averaging over quadratic combinations of the derivatives of CMB
field. We test the method using simulations and show that it can successfully
recover projected density profile of a cluster of galaxies if there are
measurable anisotropies on scales smaller than the characteristic cluster size.
In the absence of sufficient small scale power the reconstructed maps have low
signal to noise on individual structures, but can give a positive detection of
the power spectrum or when cross correlated with other maps of large scale
structure. We develop an analytic method to reconstruct the power spectrum
including the effects of noise and beam smoothing. Tests with Monte Carlo
simulations show that we can recover the input power spectrum both on large and
small scales, provided that we use maps with sufficiently low noise and high
angular resolution.Comment: 21 pages, 9 figures, submitted to PR
Evidence of a large seasonal coastal upwelling system along the southern shelf of Australia
2000 FLORIDA AVE NW, WASHINGTON, USA, DC,
2000
CMB B-polarization to map the Large-scale Structures of the Universe
We explore the possibility of using the B-type polarization of the CMB to map
the large-scale structures of the Universe taking advantage of the lens effects
on the CMB polarization. The functional relation between the B component with
the primordial CMB polarization and the line-of-sight mass distribution is
explicited. Noting that a sizeable fraction (at least 40%) of the dark halo
population which is responsible of this effect can also be detected in galaxy
weak lensing survey, we present statistical quantities that should exhibit a
strong sensitivity to this overlapping. We stress that it would be a sound test
of the gravitational instability picture, independent on many systematic
effects that may hamper lensing detection in CMB or galaxy survey alone.
Moreover we estimate the intrinsic cosmic variance of the amplitude of this
effect to be less than 8% for a 100, deg^2 survey with a 10' CMB beam. Its
measurement would then provide us with an original mean for constraining the
cosmological parameters, more particularly, as it turns out, the cosmological
constant Lambda.Comment: Latex2e with REVTEX ; 14 pages, 8 figure
Conduction and cooling flows
Chandra and XMM-Newton observations have confirmed the presence of large
temperature gradients within the cores of many relaxed clusters of galaxies.
Here we investigate whether thermal conduction operating over those gradients
can supply sufficient heat to offset radiative cooling. Narayan & Medvedev
(2001) and Gruzinov (2002) have noted, using published results on cluster
temperatures, that conduction within a factor of a few of the Spitzer rate is
sufficient to balance bremsstrahlung cooling. From a detailed study of the
temperature and emission measure profiles of Abell 2199 and Abell 1835, we find
that the heat flux required by conduction is consistent with or below the rate
predicted by Spitzer in the outer regions of the core. Conduction may therefore
explain the lack of observational evidence for large mass cooling rates
inferred from arguments based simply on radiative cooling, provided that
conductivity is suppressed by no more than a factor of three below the full
Spitzer rate. To stem cooling in the cluster centre, however, would necessitate
conductivity values at least a factor of two larger than the Spitzer values,
which we consider implausible. This may provide an explanation for the observed
star formation and optical nebulosities in cluster cores. The solution is
likely to be time dependent. We briefly discuss the possible origin of the
cooler gas and the implications for massive galaxies.Comment: 5 pages, 4 figures, accepted by MNRAS. Minor changes following
referee's comment
Comparison of the Sachs-Wolfe Effect for Gaussian and Non-Gaussian Fluctuations
A consequence of non-Gaussian perturbations on the Sachs-Wolfe effect is
studied. For a particular power spectrum, predicted Sachs-Wolfe effects are
calculated for two cases: Gaussian (random phase) configuration, and a specific
kind of non-Gaussian configuration. We obtain a result that the Sachs-Wolfe
effect for the latter case is smaller when each temperature fluctuation is
properly normalized with respect to the corresponding mass fluctuation . The physical explanation and the generality of the result are
discussed.Comment: 16 page
Systematic Errors in the Hubble Constant Based on Measurement of the Sunyaev-Zeldovich Effect
Values of the Hubble constant reported to date which are based on measurement
of the Sunyaev-Zeldovich (SZ) effect in clusters of galaxies are systematically
lower than those derived by other methods (e.g., Cepheid variable stars, or the
Tully-Fisher relation). We investigate the possibility that systematic errors
may be introduced into the analysis by the generally adopted assumptions that
observed clusters are in hydrostatic equilibrium, are spherically symmetric,
and are isothermal. We construct self-consistent theoretical models of merging
clusters of galaxies using hydrodynamical/N-body simulations. We then compute
the magnitude of Ho derived from the SZ effect at different times and at
different projection angles both from first principles, and by applying each of
the standard assumptions used in the interpretation of observations. Our
results indicate that the assumption of isothermality in the evolving clusters
can result in Ho being underestimated by 10-30% depending on both epoch and
projection angle. Moreover, use of the projected, emission-weighted temperature
profile under the assumption of spherical symmetry does not significantly
improve the situation except in the case of more extreme mergers (i.e., those
involving relatively gas-rich subclusters).Comment: 31 pages, Latex, 2 tables, 10 postscript figures, Accepted for
publication in ApJ, scheduled for June 20, 199
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