48 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
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
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
Measuring our universe from galaxy redshift surveys
Galaxy redshift surveys have achieved significant progress over the last
couple of decades. Those surveys tell us in the most straightforward way what
our local universe looks like. While the galaxy distribution traces the bright
side of the universe, detailed quantitative analyses of the data have even
revealed the dark side of the universe dominated by non-baryonic dark matter as
well as more mysterious dark energy (or Einstein's cosmological constant). We
describe several methodologies of using galaxy redshift surveys as cosmological
probes, and then summarize the recent results from the existing surveys.
Finally we present our views on the future of redshift surveys in the era of
Precision Cosmology.Comment: 82 pages, 31 figures, invited review article published in Living
Reviews in Relativity, http://www.livingreviews.org/lrr-2004-
The effect of non--gravitational gas heating in groups and clusters of galaxies
We present a set of gas-dynamical simulations of galaxy groups and clusters
aimed at exploring the effect of non-gravitational heating. We use GASOLINE, a
parallel Tree+SPH code, to simulate the formation of four cosmic halos with
temperature 0.5<T<8 keV. Non-gravitational heating is implemented in two
different ways: (1) by imposing a minimum entropy floor at a given redshift,
1<z<5; (2) by gradually heating gas, proportionally to the SN rate expected
from semi-analytical modeling of galaxy formation. Our main results are the
following. (a) An extra heating energy of about 1 keV per gas particle is
required to reproduce the observed Lx-T relation, independent of whether it is
provided so as to create an entropy floor of 50-100 keV cm^2, or is modulated
in redshift; our SN feedback recipe provides only 1/3 keV/part. (b) The M-T
relation is almost unaffected by non-gravitational heating and follows the M
T^{3/2} scaling, with a normalization ~40% higher than observed, independent of
the heating scheme. The inclusion of cooling in a run of a small group has the
effects of increasing T_ew by ~30%, possibly reconciling simulated and observed
M-T relations, and of decreasing Lx by ~40%. In spite of the inclusion of SN
feedback energy, almost 40% of the gas becomes cold, in excess of current
observational estimates. (abridged)Comment: 18 pages, 15 figures, to appear in MNRAS. Version with high
resolution images available at
http://www.daut.univ.trieste.it/borgani/LT/lt_1.ps.g
The Formation of the First Stars in the Universe
In this review, I survey our current understanding of how the very first
stars in the universe formed, with a focus on three main areas of interest: the
formation of the first protogalaxies and the cooling of gas within them, the
nature and extent of fragmentation within the cool gas, and the physics -- in
particular the interplay between protostellar accretion and protostellar
feedback -- that serves to determine the final stellar mass.
In each of these areas, I have attempted to show how our thinking has
developed over recent years, aided in large part by the increasing ease with
which we can now perform detailed numerical simulations of primordial star
formation. I have also tried to indicate the areas where our understanding
remains incomplete, and to identify some of the most important unsolved
problems.Comment: 74 pages, 4 figures. Accepted for publication in Space Science
Review