68 research outputs found
Galaxy Zoo: Disentangling the Environmental Dependence of Morphology and Colour
We analyze the environmental dependence of galaxy morphology and colour with
two-point clustering statistics, using data from the Galaxy Zoo, the largest
sample of visually classified morphologies yet compiled, extracted from the
Sloan Digital Sky Survey. We present two-point correlation functions of spiral
and early-type galaxies, and we quantify the correlation between morphology and
environment with marked correlation functions. These yield clear and precise
environmental trends across a wide range of scales, analogous to similar
measurements with galaxy colours, indicating that the Galaxy Zoo
classifications themselves are very precise. We measure morphology marked
correlation functions at fixed colour and find that they are relatively weak,
with the only residual correlation being that of red galaxies at small scales,
indicating a morphology gradient within haloes for red galaxies. At fixed
morphology, we find that the environmental dependence of colour remains strong,
and these correlations remain for fixed morphology \textit{and} luminosity. An
implication of this is that much of the morphology--density relation is due to
the relation between colour and density. Our results also have implications for
galaxy evolution: the morphological transformation of galaxies is usually
accompanied by a colour transformation, but not necessarily vice versa. A
spiral galaxy may move onto the red sequence of the colour-magnitude diagram
without quickly becoming an early-type. We analyze the significant population
of red spiral galaxies, and present evidence that they tend to be located in
moderately dense environments and are often satellite galaxies in the outskirts
of haloes. Finally, we combine our results to argue that central and satellite
galaxies tend to follow different evolutionary paths.Comment: 19 pages, 18 figures. Accepted for publication in MNRA
Predominant Asymmetrical Stem Cell Fate Outcome Limits the Rate of Niche Succession in Human Colonic Crypts.
Stem cell (SC) dynamics within the human colorectal crypt SC niche remain poorly understood, with previous studies proposing divergent hypotheses on the predominant mode of SC self-renewal and the rate of SC replacement. Here we use age-related mitochondrial oxidative phosphorylation (OXPHOS) defects to trace clonal lineages within human colorectal crypts across the adult life-course. By resolving the frequency and size distribution of OXPHOS-deficient clones, quantitative analysis shows that, in common with mouse, long-term maintenance of the colonic epithelial crypt relies on stochastic SC loss and replacement mediated by competition for limited niche access. We find that the colonic crypt is maintained by ~5 effective SCs. However, with a SC loss/replacement rate estimated to be slower than once per year, our results indicate that the vast majority of individual SC divisions result in asymmetric fate outcome. These findings provide a quantitative platform to detect and study deviations from human colorectal crypt SC niche homeostasis during the process of colorectal carcinogenesis.Wellcome Trus
First results from the Very Small Array -- I. Observational methods
The Very Small Array (VSA) is a synthesis telescope designed to image faint
structures in the cosmic microwave background on degree and sub-degree angular
scales. The VSA has key differences from other CMB interferometers with the
result that different systematic errors are expected. We have tested the
operation of the VSA with a variety of blank-field and calibrator observations
and cross-checked its calibration scale against independent measurements. We
find that systematic effects can be suppressed below the thermal noise level in
long observations; the overall calibration accuracy of the flux density scale
is 3.5 percent and is limited by the external absolute calibration scale.Comment: 9 pages, 10 figures, MNRAS in press (Minor revisions
First results from the Very Small Array -- III. The CMB power spectrum
We present the power spectrum of the fluctuations in the cosmic microwave
background detected by the Very Small Array (VSA) in its first season of
observations in its compact configuration. We find clear detections of first
and second acoustic peaks at l~200 and l~550, plus detection of power on scales
up to l=800. The VSA power spectrum is in very good agreement with the results
of the Boomerang, Dasi and Maxima telescopes despite the differing potential
systematic errors.Comment: 10 pages, 6 figure, MNRAS in press. (Minor revisions - accepted 17
December 2002
Present bounds on the relativistic energy density in the Universe from cosmological observables
We discuss the present bounds on the relativistic energy density in the
Universe parameterized in terms of the effective number of neutrinos N using
the most recent cosmological data on Cosmic Microwave Background (CMB)
temperature anisotropies and polarization, Large Scale galaxy clustering from
the Sloan Digital Sky Survey (SDSS) and 2dF, luminosity distances of type Ia
Supernovae, Lyman-alpha absorption clouds (Ly-alpha), the Baryonic Acoustic
Oscillations (BAO) detected in the Luminous Red Galaxies of the SDSS and
finally, Big Bang Nucleosynthesis (BBN) predictions for 4He and Deuterium
abundances. We find N= 5.2+2.7-2.2 from CMB and Large Scale Structure data,
while adding Ly-alpha and BAO we obtain N= 4.6+1.6-1.5 at 95 % c.l.. These
results show some tension with the standard value N=3.046 as well as with the
BBN range N= 3.1+1.4-1.2 at 95 % c.l., though the discrepancy is slightly below
the 2-sigma level. In general, considering a smaller set of data weakens the
constraints on N. We emphasize the impact of an improved upper limit (or
measurement) of the primordial value of 3He abundance in clarifying the issue
of whether the value of N at early (BBN) and more recent epochs coincide
First results from the Very Small Array -- II. Observations of the CMB
We have observed the cosmic microwave background temperature fluctuations in
eight fields covering three separated areas of sky with the Very Small Array at
34 GHz. A total area of 101 square degrees has been imaged, with sensitivity on
angular scales 3.6 - 0.4 degrees (equivalent to angular multipoles l=150-900).
We describe the field selection and observing strategy for these observations.
In the full-resolution images (with synthesised beam of FWHM ~ 17 arcmin) the
thermal noise is typically 45 microK and the CMB signal typically 55 microK.
The noise levels in each field agree well with the expected thermal noise level
of the telescope, and there is no evidence of any residual systematic features.
The same CMB features are detected in separate, overlapping observations.
Discrete radio sources have been detected using a separate 15 GHz survey and
their effects removed using pointed follow-up observations at 34 GHz. We
estimate that the residual confusion noise due to unsubtracted radio sources is
less than 14 mJy/beam (15 microK in the full-resolution images), which added in
quadrature to the thermal noise increases the noise level by 6 %. We estimate
that the rms contribution to the images from diffuse Galactic emission is less
than 6 microK. We also present images which are convolved to maximise the
signal-to-noise of the CMB features and are co-added in overlapping areas, in
which the signal-to-noise of some individual CMB features exceeds 8.Comment: 11 pages, 5 figures, accepted for publication in MNRAS. Replaces
original version - more detailed abstract, corrected typo
The CMB power spectrum out to l=1400 measured by the VSA
We have observed the cosmic microwave background (CMB) in three regions of
sky using the Very Small Array (VSA) in an extended configuration with antennas
of beamwidth 2 degrees at 34 GHz. Combined with data from previous VSA
observations using a more compact array with larger beamwidth, we measure the
power spectrum of the primordial CMB anisotropies between angular multipoles l
= 160 - 1400. Such measurements at high l are vital for breaking degeneracies
in parameter estimation from the CMB power spectrum and other cosmological
data. The power spectrum clearly resolves the first three acoustic peaks, shows
the expected fall off in power at high l and starts to constrain the position
and height of a fourth peak.Comment: 6 pages with 5 figures, MNRAS in press (minor corrections
Non-Gaussianity in the Very Small Array CMB maps with Smooth-Goodness-of-fit tests
(Abridged) We have used the Rayner & Best (1989) smooth tests of
goodness-of-fit to study the Gaussianity of the Very Small Array (VSA) data.
Out of the 41 published VSA individual pointings dedicated to cosmological
observations, 37 are found to be consistent with Gaussianity, whereas four
pointings show deviations from Gaussianity. In two of them, these deviations
can be explained as residual systematic effects of a few visibility points
which, when corrected, have a negligible impact on the angular power spectrum.
The non-Gaussianity found in the other two (adjacent) pointings seems to be
associated to a local deviation of the power spectrum of these fields with
respect to the common power spectrum of the complete data set, at angular
scales of the third acoustic peak (l = 700-900). No evidence of residual
systematics is found in this case, and unsubstracted point sources are not a
plausible explanation either. If those visibilities are removed, a cosmological
analysis based on this new VSA power spectrum alone shows no differences in the
parameter constraints with respect to our published results, except for the
physical baryon density, which decreases by 10 percent. Finally, the method has
been also used to analyse the VSA observations in the Corona Borealis
supercluster region (Genova-Santos et al. 2005), which show a strong decrement
which cannot be explained as primordial CMB. Our method finds a clear deviation
(99.82%) with respect to Gaussianity in the second-order moment of the
distribution, and which can not be explained as systematic effects. A detailed
study shows that the non-Gaussianity is produced in scales of l~500, and that
this deviation is intrinsic to the data (in the sense that can not be explained
in terms of a Gaussian field with a different power spectrum).Comment: 14 pages, 7 figures. Accepted for publication in MNRA
Core Cosmology Library: Precision Cosmological Predictions for LSST
The Core Cosmology Library (CCL) provides routines to compute basic
cosmological observables to a high degree of accuracy, which have been verified
with an extensive suite of validation tests. Predictions are provided for many
cosmological quantities, including distances, angular power spectra,
correlation functions, halo bias and the halo mass function through
state-of-the-art modeling prescriptions available in the literature. Fiducial
specifications for the expected galaxy distributions for the Large Synoptic
Survey Telescope (LSST) are also included, together with the capability of
computing redshift distributions for a user-defined photometric redshift model.
A rigorous validation procedure, based on comparisons between CCL and
independent software packages, allows us to establish a well-defined numerical
accuracy for each predicted quantity. As a result, predictions for correlation
functions of galaxy clustering, galaxy-galaxy lensing and cosmic shear are
demonstrated to be within a fraction of the expected statistical uncertainty of
the observables for the models and in the range of scales of interest to LSST.
CCL is an open source software package written in C, with a python interface
and publicly available at https://github.com/LSSTDESC/CCL.Comment: 38 pages, 18 figures, matches ApJS accepted versio
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