776 research outputs found
Features in the Primordial Spectrum from WMAP: A Wavelet Analysis
Precise measurements of the anisotropies in the cosmic microwave background
enable us to do an accurate study on the form of the primordial power spectrum
for a given set of cosmological parameters. In a previous paper (Shafieloo and
Souradeep 2004), we implemented an improved (error sensitive) Richardson-Lucy
deconvolution algorithm on the measured angular power spectrum from the first
year of WMAP data to determine the primordial power spectrum assuming a
concordance cosmological model. This recovered spectrum has a likelihood far
better than a scale invariant, or, `best fit' scale free spectra (\Delta ln L =
25 w.r.t. Harrison Zeldovich, and, \Delta ln L = 11 w.r.t. power law with
n_s=0.95). In this paper we use Discrete Wavelet Transform (DWT) to decompose
the local features of the recovered spectrum individually to study their effect
and significance on the recovered angular power spectrum and hence the
likelihood. We show that besides the infra-red cut off at the horizon scale,
the associated features of the primordial power spectrum around the horizon
have a significant effect on improving the likelihood. The strong features are
localised at the horizon scale.Comment: 8 pages, 4 figures, uses Revtex4, matches version accepted to Phys.
Rev. D, main results and conclusions unchanged, references adde
Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. III. Power spectrum analysis and excess isotropic component of fluctuations
The cosmic infrared background (CIB) radiation is the cosmic repository for
energy release throughout the history of the universe. Using the all-sky data
from the COBE DIRBE instrument at wavelengths 1.25 - 100 mic we attempt to
measure the CIB fluctuations. In the near-IR, foreground emission is dominated
by small scale structure due to stars in the Galaxy. There we find a strong
correlation between the amplitude of the fluctuations and Galactic latitude
after removing bright foreground stars. Using data outside the Galactic plane
() and away from the center () we extrapolate
the amplitude of the fluctuations to cosec. We find a positive intercept
of nW/m2/sr at 1.25, 2.2,3.5 and 4.9 mic
respectively, where the errors are the range of 92% confidence limits. For
color subtracted maps between band 1 and 2 we find the isotropic part of the
fluctuations at nW/m2/sr. Based on detailed numerical and
analytic models, this residual is not likely to originate from the Galaxy, our
clipping algorithm, or instrumental noise. We demonstrate that the residuals
from the fit used in the extrapolation are distributed isotropically and
suggest that this extra variance may result from structure in the CIB. For
2\deg< \theta < 15^\deg, a power-spectrum analysis yields firm upper limits
of (\theta/5^\deg) \times\delta F_{\rm rms} (\theta) < 6, 2.5, 0.8, 0.5
nW/m2/sr at 1.25, 2.2, 3.5 and 4.9 mic respectively. From 10-100 mic, the upper
limits <1 nW/m2/sr.Comment: Ap.J., in press. 69 pages including 24 fig
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 moving mesh hydro simulation and estimate that the ROSAT
all sky survey plus Sloan galaxy photometric redshift survey would allow a
accuracy in the IGM XRB-galaxy cross correlation power spectrum
measurement for and a accuracy in the redshift resolved
X-ray emissivity-galaxy cross correlation power spectrum measurement for
. 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.Comment: 17 pages, 5 figures. Will appear on ApJ May issu
A High Merger Fraction in the Rich Cluster MS1054-03 at z=0.83: Direct Evidence for Hierarchical Formation of Massive Galaxies
We present a morphological study of the galaxy population of the luminous
X-ray cluster MS1054-03 at z=0.83. The sample consists of 81 spectroscopically
confirmed cluster members in a 3 x 2 Mpc area imaged in F606W and F814W with
WFPC2. We find thirteen ongoing mergers in MS1054-03, comprising 17% of the L >
L* cluster population. Most of these mergers will likely evolve into luminous
(\sim 2 L*) elliptical galaxies, and some may evolve into S0 galaxies. Assuming
the galaxy population in MS1054-03 is typical for its redshift it is estimated
that \sim 50% of present-day cluster ellipticals experienced a major merger at
z < 1. The mergers are preferentially found in the outskirts of the cluster,
and probably occur in small infalling clumps. Morphologies, spectra, and colors
of the mergers show that their progenitors were typically E/S0s or early-type
spirals with mean stellar formation redshifts z* \gtrsim 1.7. The red colors of
the merger remnants are consistent with the low scatter in the color-magnitude
relation in rich clusters at lower redshift. The discovery of a high fraction
of mergers in this young cluster is direct evidence against formation of
ellipticals in a single ``monolithic'' collapse at high redshift, and in
qualitative agreement with predictions of hierarchical models for structure
formation.Comment: Added GIF version of Figure 1. At
http://www.astro.rug.nl/~dokkum/preprints/merger_fig1.eps.gz the PS file is
available. Accepted for publication in ApJ Letter
Constraints On the Size Evolution of Brightest Cluster Galaxies
We measure the luminosity profiles of 16 brightest cluster galaxies (BCGs) at
using high resolution F160W NICMOS and F814W WFPC2 HST imaging.
The heterogeneous sample is drawn from a variety of surveys: seven from
clusters in the Einstein Medium Sensitivity Survey, five from the Las Campanas
Distant Cluster Survey and its northern hemisphere precursor, and the remaining
four from traditional optical surveys. We find that the surface brightness
profiles of all but three of these BCGs are well described by a standard de
Vaucouleurs () profile out to at least and that the
biweight-estimated NICMOS effective radius of our high redshift BCGs ( kpc for km s Mpc, ) is times smaller than that measured for a local
BCG sample. If high redshift BCGs are in dynamical equilibrium and satisfy the
same scaling relations as low redshift ones, this change in size would
correspond to a mass growth of a factor of 2 since . However, the
biweight-estimated WFPC2 effective radius of our sample is 18 5.1 kpc,
which is fully consistent with the local sample. While we can rule out mass
accretion rates higher than a factor of 2 in our sample, the discrepancy
between our NICMOS and WFPC2 results, which after various tests we describe
appears to be physical, does not yet allow us to place strong constraints on
accretion rates below that level.Comment: ApJ accepted (566, 1, February 2002), 12 pages, uses emulateapj5.st
Can We Detect the Color–Density Relation with Photometric Redshifts?
A variety of methods have been proposed to define and to quantify galaxy environments. While these techniques work well in general with spectroscopic redshift samples, their application to photometric redshift surveys remains uncertain. To investigate whether galaxy environments can be robustly measured with photo-z samples, we quantify how the density measured with the nearest-neighbor approach is affected by photo-z uncertainties by using the Durham mock galaxy catalogs in which the 3D real-space environments and the properties of galaxies are known exactly. Furthermore, we present an optimization scheme in the choice of parameters used in the 2D projected measurements that yield the tightest correlation with respect to the 3D real-space environments. By adopting the optimized parameters in the density measurements, we show that the correlation between the 2D projected optimized density and the real-space density can still be revealed, and the color–density relation is also visible out to z ~ 0.8 even for a photo-z uncertainty () up to 0.06. We find that at redshifts 0.3 < z < 0.5 a deep (i ~ 25) photometric redshift survey with yields a performance in small-scale density measurement that is comparable to a shallower i ~ 22.5 spectroscopic sample with ~10% sampling rate. Finally, we discuss the application of the local density measurements to the Pan-STARRS1 Medium Deep Survey (PS-MDS), one of the largest deep optical imaging surveys. Using data from ~5 square degrees of survey area, our results show that it is possible to measure local density and to probe the color–density relation with 3σ confidence level out to z ~ 0.8 in the PS-MDS. The color–density relation, however, quickly degrades for data covering smaller areas
Hormonal Signal Amplification Mediates Environmental Conditions during Development and Controls an Irreversible Commitment to Adulthood
Many animals can choose between different developmental fates to maximize fitness. Despite the complexity of environmental cues and life history, different developmental fates are executed in a robust fashion. The nematode Caenorhabditis elegans serves as a powerful model to examine this phenomenon because it can adopt one of two developmental fates (adulthood or diapause) depending on environmental conditions. The steroid hormone dafachronic acid (DA) directs development to adulthood by regulating the transcriptional activity of the nuclear hormone receptor DAF-12. The known role of DA suggests that it may be the molecular mediator of environmental condition effects on the developmental fate decision, although the mechanism is yet unknown. We used a combination of physiological and molecular biology techniques to demonstrate that commitment to reproductive adult development occurs when DA levels, produced in the neuroendocrine XXX cells, exceed a threshold. Furthermore, imaging and cell ablation experiments demonstrate that the XXX cells act as a source of DA, which, upon commitment to adult development, is amplified and propagated in the epidermis in a DAF-12 dependent manner. This positive feedback loop increases DA levels and drives adult programs in the gonad and epidermis, thus conferring the irreversibility of the decision. We show that the positive feedback loop canalizes development by ensuring that sufficient amounts of DA are dispersed throughout the body and serves as a robust fate-locking mechanism to enforce an organism-wide binary decision, despite noisy and complex environmental cues. These mechanisms are not only relevant to C. elegans but may be extended to other hormonal-based decision-making mechanisms in insects and mammals
The Luminosity Function Of Field Galaxies And Its Evolution Since z=1
We present the B-band luminosity function and comoving space and luminosity
densities for a sample of 2779 I-band selected field galaxies based on
multi-color data from the CADIS survey. The sample is complete down to I_815 =
22 without correction and with completeness correction extends to I_815=23.0.
By means of a new multi-color analysis the objects are classified according to
their spectral energy distributions (SEDs) and their redshifts are determined
with typical errors of delta z <= 0.03. We have split our sample into four
redshift bins between z=0.1 and z=1.04 and into three SED bins E-Sa,Sa-Sc and
starbursting (emission line) galaxies. The evolution of the luminosity function
is clearly differential with SED. The normalization phi* of luminosity function
for the E-Sa galaxies decreases towards higher redshift, and we find evidence
that the comoving galaxy space density decreases with redshift as well. In
contrast, we find phi* and the comoving space density increasing with redshift
for the Sa-Sc galaxies. For the starburst galaxies we find a steepening of the
luminosity function at the faint end and their comoving space density increases
with redshift.Comment: 15 pages, 14 figures, accepted by Astronomy&Astrophysic
The Canada-UK Deep Submillimeter Survey VI: The 3-Hour Field
We present the complete submillimeter data for the Canada-UK Deep
Submillimeter Survey (CUDSS) 3-hour field. The obeservations were taken with
the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk
Maxwell Telescope on Mauna Kea. The 3-hour field is one of two main fields in
our survey and covers 60 square arcminutes to a 3-sigma depth of 3 mJy. In this
field we have detected 27 sources above 3-sigma and 15 above 3.5-sigma. We
assume the source counts follow the form and
measure = 3.3. This is in good agreement with previous
studies and further supports our claim (Eales et al., 2000) that SCUBA sources
brighter than 3 mJy produce ~20% of the 850m background energy. Using
preliminary ISO 15 m maps and VLA 1.4 GHz data we have identified
counterparts for six objects and have marginal detections at 450m for two
additional sources. With this information we estimate a median redshift for the
sample of 2.00.5, with 10% lying at 1. We have measured the
angular clustering of S850 > 3 mJy sources using the source catalogues from the
CUDSS two main fields, the 3-hour and 14-hour fields, and find a marginal
detection of clustering, primarily from the 14-hour field, of
. This is consistent with clustering at
least as strong as that seen for the Lyman-break galaxy population and the
Extremely Red Objects. Since SCUBA sources are selected over a broader range in
redshifts than these two populations the strength of the true spatial
clustering is expected to be correspondingly stronger.Comment: 17 pages, 8 figures, submitted to Ap
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