3,293 research outputs found
Halo stochasticity in global clustering analysis
In the present work we study the statistics of haloes, which in the halo
model determines the distribution of galaxies. Haloes are known to be biased
tracer of dark matter, and at large scales it is usually assumed there is no
intrinsic stochasticity between the two fields. Following the work of Seljak &
Warren (2004), we explore how correct this assumption is and, moving a step
further, we try to qualify the nature of stochasticity. We use Principal
Component Analysis applied to the outputs of a cosmological N-body simulation
to: (1) explore the behaviour of stochasticity in the correlation between
haloes of different masses; (2) explore the behaviour of stochasticity in the
correlation between haloes and dark matter. We show results obtained using a
catalogue with 2.1 million haloes, from a PMFAST simulation with box size of
1000h^{-1}Mpc. In the relation between different populations of haloes we find
that stochasticity is not-negligible even at large scales. In agreement with
the conclusions of Tegmark & Bromley (1999) who studied the correlations of
different galaxy populations, we found that the shot-noise subtracted
stochasticity is qualitatively different from `enhanced' shot noise and,
specifically, it is dominated by a single stochastic eigenvalue. We call this
the `minimally stochastic' scenario, as opposed to shot noise which is
`maximally stochastic'. In the correlation between haloes and dark matter, we
find that stochasticity is minimized, as expected, near the dark matter peak (k
~ 0.02 h Mpc^{-1} for a LambdaCDM cosmology) and, even at large scales, it is
of the order of 15 per cent above the shot noise. Moreover, we find that the
reconstruction of the dark matter distribution is improved when we use
eigenvectors as tracers of the bias. [Abridged]Comment: 9 pages, 12 figures. Submitted to MNRA
Objective and Subjective Factors as Predictors of Post-Traumatic Stress Symptoms in Parents of Children with Cancer – A Longitudinal Study
BACKGROUND: Parents of children with cancer report post-traumatic stress symptoms (PTSS) years after the child's successful treatment is completed. The aim of the present study was to analyze a number of objective and subjective childhood cancer-related factors as predictors of parental PTSS. METHODS: Data were collected from 224 parents during and after their child's cancer treatment. Data sources include self-report questionnaires and medical records. RESULTS: In a multivariate hierarchical model death of the child, parent's perception of child psychological distress and total symptom burden predicted higher levels of PTSS. In addition, immigrants and unemployed parents reported higher levels of PTSS. The following factors did not predict PTSS: parent gender, family income, previous trauma, child's prognosis, treatment intensity, non-fatal relapse, and parent's satisfaction with the child's care. CONCLUSIONS: Although medical complications can be temporarily stressful, a parent's perception of the child's distress is a more powerful predictor of parental PTSS. The vulnerability of unemployed parents and immigrants should be acknowledged. In addition, findings highlight that the death of a child is as traumatic as could be expected
Wing shape patterns among urban, suburban, and rural populations of Ischnura elegans (Odonata: Coenagrionidae)
Dragonflies and damselflies (the Odonata) are among the most efficient flying insects. However, fragmentation of the landscape can increase distance between habitats and affect costs of dispersal, thus shaping phenotypic patterns of flight-related traits, such as wing shape, wing loading and wing size. Urban landscapes are highly fragmented, which limits dispersal among aquatic habitats. Hence, strong selective pressures can act upon urban populations in favour of individuals with increased flight performance or may lead to the reduction in dispersal traits. Here, we explore differentiation in morphological flight-related traits among urban, suburban, and rural populations of the damselfly Ischnura elegans, which is one of the most abundant species in both urban and rural ponds in Europe. We sampled 20 sites across Leeds and Bradford, UK, in an urban-to-rural gradient from June to August 2014 and 2015 (Nmales = 201, Nfemales = 119). We compared wing shape among different land use types using geometric morphometrics. Other wing properties analysed were wing aspect ratio, wing loading and wing centroid size. Unexpectedly, no significant effect of urban land use was found on wing shape. However, wing shape differed significantly between males and females. Additionally, females showed significantly larger wing centroid sizes (P < 0.001), increased wing loading (forewings: P = 0.007; hind wings: P = 0.002) and aspect ratio (P < 0.001) compared to males across all land use types. Possible mechanisms driving these results are further discussed
Photometric Selection of Emission Line Galaxies, Clustering Analysis and a Search for the ISW effect
We investigate the use of simple colour cuts applied to the SDSS optical
imaging to perform photometric selections of emission line galaxies out to z<1.
From colour-cuts using the SDSS g, r and i bands, we obtain mean photometric
redshifts of z=0.32+-0.08, z=0.44+-0.12 and z=0.65+-0.21. We further calibrate
our high redshift selection using spectroscopic observations with the AAOmega
spectrograph on the 4m Anglo-Australian Telescope (AAT), observing ~50-200
galaxy candidates in 4 separate fields. With just 1-hour of integration time
and with seeing of ~1.6", we successfully determined redshifts for ~65% of the
targeted candidates. We calculate the angular correlation functions of the
samples and find correlation lengths of r0=2.64 h-1 Mpc, r0=3.62 h-1 Mpc and
r0=5.88 h-1 Mpc for the low, mid and high redshift samples respectively.
Comparing these results with predicted dark matter clustering, we estimate the
bias parameter for each sample to be b=0.70, b=0.92 and b=1.46. We calculate
the 2-point redshift-space correlation function at z~0.6 and find a clustering
amplitude of s0=6.4 h-1 Mpc. Finally, we use our photometric sample to search
for the Integrated Sachs-Wolfe signal in the WMAP 5yr data. We cross-correlate
our three redshift samples with the WMAP W, V, Q and K bands and find an
overall trend for a positive signal similar to that expected from models.
However, the signal in each is relatively weak. Combining all three galaxy
samples we find a signal of wTg(<100')=0.20+-0.12 microK in the WMAP W-band, a
significance of 1.7sigma.Comment: 14 pages, 17 figures, submitted to MNRA
The zCOSMOS Survey. The dependence of clustering on luminosity and stellar mass at z=0.2-1
We study the dependence of galaxy clustering on luminosity and stellar mass
at redshifts z ~ [0.2-1] using the first zCOSMOS 10K sample.
We measure the redshift-space correlation functions xi(rp,pi) and its
projection wp(rp) for sub-samples covering different luminosity, mass and
redshift ranges. We quantify in detail the observational selection biases and
we check our covariance and error estimate techniques using ensembles of
semi-analytic mock catalogues. We finally compare our measurements to the
cosmological model predictions from the mock surveys.
At odds with other measurements, we find a weak dependence of galaxy
clustering on luminosity in all redshift bins explored. A mild dependence on
stellar mass is instead observed. At z~0.7, wp(rp) shows strong excess power on
large scales. We interpret this as produced by large-scale structure dominating
the survey volume and extending preferentially in direction perpendicular to
the line-of-sight. We do not see any significant evolution with redshift of the
amplitude of clustering for bright and/or massive galaxies.
The clustering measured in the zCOSMOS data at 0.5<z<1 for galaxies with
log(M/M_\odot)>=10 is only marginally consistent with predictions from the mock
surveys. On scales larger than ~2 h^-1 Mpc, the observed clustering amplitude
is compatible only with ~1% of the mocks. Thus, if the power spectrum of matter
is LCDM with standard normalization and the bias has no unnatural
scale-dependence, this result indicates that COSMOS has picked up a
particularly rare, ~2-3 sigma positive fluctuation in a volume of ~10^6 h^-1
Mpc^3. These findings underline the need for larger surveys of the z~1 Universe
to appropriately characterize the level of structure at this epoch.Comment: 18 pages, 21 figures, accepted for publication in Astronomy and
Astrophysic
The VIMOS-VLT Deep Survey. The dependence of clustering on galaxy stellar mass at z~1
Aims: We use the VVDS-Deep first-epoch data to measure the dependence of
galaxy clustering on galaxy stellar mass, at z~0.85.
Methods: We measure the projected correlation function wp(rp) for sub-samples
with 0.5<z<1.2 covering different mass ranges between 10^9 and 10^11 Msun. We
quantify in detail the observational selection biases using 40 mock catalogues
built from the Millennium run and semi-analytic models.
Results: Our simulations indicate that serious incompleteness in mass is
present only for log(M/Msun)<9.5. In the mass range log(M/Msun)=[9.0-9.5], the
photometric selection function of the VVDS misses 2/3rd of the galaxies. The
sample is virtually 100% complete above 10^10 Msun. We present the first direct
evidence for a clear dependence of clustering on the galaxy stellar mass at
z~0.85. The clustering length increases from r0 ~ 2.76 h^-1 Mpc for galaxies
with mass M>10^9 Msun to r0 ~ 4.28 h^-1 Mpc for galaxies more massive than
10^10.5 Msun. At the same time, the slope increases from ~ 1.67 to ~ 2.28.
A comparison of the observed wp(rp) to local measurements by the SDSS shows
that the evolution is faster for objects less massive than ~10^10.5 Msun. This
is interpreted as a higher dependence on redshift of the linear bias b_L for
the more massive objects. While for the most massive galaxies b_L decreases
from 1.5+/-0.2 at z~0.85 to 1.33+/-0.03 at z~0.15, the less massive population
maintains a virtually constant value b_L~1.3. This result is in agreement with
a scenario in which more massive galaxies formed at high redshift in the
highest peaks of the density field, while less massive objects form at later
epochs from the more general population of dark-matter halos.Comment: 13 pages, 10 figures, accepted in A&
Spatial Periodicity of Galaxy Number Counts, CMB Anisotropy, and SNIa Hubble Diagram Based on the Universe Accompanied by a Non-Minimally Coupled Scalar Field
We have succeeded in establishing a cosmological model with a non-minimally
coupled scalar field that can account not only for the spatial
periodicity or the {\it picket-fence structure} exhibited by the galaxy -
relation of the 2dF survey but also for the spatial power spectrum of the
cosmic microwave background radiation (CMB) temperature anisotropy observed by
the WMAP satellite. The Hubble diagram of our model also compares well with the
observation of Type Ia supernovae. The scalar field of our model universe
starts from an extremely small value at around the nucleosynthesis epoch,
remains in that state for sufficiently long periods, allowing sufficient time
for the CMB temperature anisotropy to form, and then starts to grow in
magnitude at the redshift of , followed by a damping oscillation
which is required to reproduce the observed picket-fence structure of the
- relation. To realize such behavior of the scalar field, we have found
it necessary to introduce a new form of potential , with being a constant. Through this parameter ,
we can control the epoch at which the scalar field starts growing.Comment: 19 pages, 18 figures, Accepted for publication in Astrophysics &
Space Scienc
Comparison of the VIMOS-VLT Deep Survey with the Munich semi-analytical model - I. Magnitude counts, redshift distribution, colour bimodality, and galaxy clustering
This paper presents a detailed comparison between high-redshift observations
from the VIMOS-VLT Deep Survey (VVDS) and predictions from the Munich
semi-analytical model of galaxy formation. In particular, we focus this
analysis on the magnitude, redshift, and colour distributions of galaxies, as
well as their clustering properties. We constructed 100 quasi-independent mock
catalogues, using the output of the semi-analytical model presented in De Lucia
& Blaizot (2007).We then applied the same observational selection function of
the VVDS-Deep survey, so as to carry out a fair comparison between models and
observations. We find that the semi-analytical model reproduces well the
magnitude counts in the optical bands. It tends, however, to overpredict the
abundance of faint red galaxies, in particular in the i' and z' bands. Model
galaxies exhibit a colour bimodality that is only in qualitative agreement with
the data. In particular, we find that the model tends to overpredict the number
of red galaxies at low redshift and of blue galaxies at all redshifts probed by
VVDS-Deep observations, although a large fraction of the bluest observed
galaxies is absent from the model. In addition, the model overpredicts by about
14 per cent the number of galaxies observed at 0.2<z<1 with I_AB<24. When
comparing the galaxy clustering properties, we find that model galaxies are
more strongly clustered than observed ones at all redshift from z=0.2 to z=2,
with the difference being less significant above z~1. When splitting the
samples into red and blue galaxies, we find that the observed clustering of
blue galaxies is well reproduced by the model, while red model galaxies are
much more clustered than observed ones, being principally responsible for the
strong global clustering found in the model. [abridged]Comment: 15 pages, 14 figures, accepted for publication in A&
Longer wings for faster springs – wing length relates tospring phenology in a long-distanc e migrant across its range
In migratory birds, morphological adaptations for efficient migratory flight often oppose morphological adaptations for efficient behavior during resident periods. This includes adaptations in wing shape for either flying long distances or foraging in the vegetation and in climate-driven variation of body size. In addition, the timing of migratory flights and particularly the timely arrival at local breeding sites is crucial because fitness prospects depend on site-specific phenology. Thus, adaptations for efficient long-distance flights might be also related to conditions at destination areas. For an obligatory long-distance migrant, the common nightingale, we verified that wing length as the aerodynamically important trait, but not structural body size increased from the western to the eastern parts of the species range. In contrast with expectation from aerodynamic theory, however, wing length did not increase with increasing migration distances. Instead, wing length was associated with the phenology at breeding destinations, namely the speed of local spring green-up. We argue that longer wings are beneficial for adjusting migration speed to local conditions for birds breeding in habitats with fast spring green-up and thus short optimal arrival periods. We suggest that the speed of spring green-up at breeding sites is a fundamental variable determining the timing of migration that fine tune phenotypes in migrants across their range
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