662 research outputs found
Cross-Correlation of spectroscopic and photometric galaxy surveys: cosmology from lensing and redshift distortions
Cosmological galaxy surveys aim at mapping the largest volumes to test models
with techniques such as cluster abundance, cosmic shear correlations or baryon
acoustic oscillations (BAO), which are designed to be independent of galaxy
bias. Here we explore an alternative route to constrain cosmology: sampling
more moderate volumes with the cross-correlation of photometric and
spectroscopic surveys. We consider the angular galaxy-galaxy autocorrelation in
narrow redshift bins and its combination with different probes of weak
gravitational lensing (WL) and redshift space distortions (RSD). Including the
cross-correlation of these surveys improves by factors of a few the constraints
on both the dark energy equation of state w(z) and the cosmic growth history,
parametrized by \gamma. The additional information comes from using many narrow
redshift bins and from galaxy bias, which is measured both with WL probes and
RSD, breaking degeneracies that are present when using each method separately.
We show forecasts for a joint w(z) and \gamma figure of merit using linear
scales over a deep (i<24) photometric survey and a brighter (i<22.5)
spectroscopic or very accurate (0.3%) photometric redshift survey.
Magnification or shear in the photometric sample produce FoM that are of the
same order of magnitude of those of RSD or BAO over the spectroscopic sample.
However, the cross-correlation of these probes over the same area yields a FoM
that is up to a factor 100 times larger. Magnification alone, without shape
measurements, can also be used for these cross-correlations and can produce
better results than using shear alone. For a spectroscopic follow-up survey
strategy, measuring the spectra of the foreground lenses to perform this
cross-correlation provides 5 times better FoM than targeting the higher
redshift tail of the galaxy distribution to study BAO over a 2.5 times larger
volume.Comment: Small cosmetic changes to match MNRAS published versio
Directed cell migration in the presence of obstacles
BACKGROUND: Chemotactic movement is a common feature of many cells and microscopic organisms. In vivo, chemotactic cells have to follow a chemotactic gradient and simultaneously avoid the numerous obstacles present in their migratory path towards the chemotactic source. It is not clear how cells detect and avoid obstacles, in particular whether they need a specialized biological mechanism to do so. RESULTS: We propose that cells can sense the presence of obstacles and avoid them because obstacles interfere with the chemical field. We build a model to test this hypothesis and find that this naturally enables efficient at-a-distance sensing to be achieved with no need for a specific and active obstacle-sensing mechanism. We find that (i) the efficiency of obstacle avoidance depends strongly on whether the chemotactic chemical reacts or remains unabsorbed at the obstacle surface. In particular, it is found that chemotactic cells generally avoid absorbing barriers much more easily than non-absorbing ones. (ii) The typically low noise in a cell's motion hinders the ability to avoid obstacles. We also derive an expression estimating the typical distance traveled by chemotactic cells in a 3D random distribution of obstacles before capture; this is a measure of the distance over which chemotaxis is viable as a means of directing cells from one point to another in vivo. CONCLUSION: Chemotactic cells, in many cases, can avoid obstacles by simply following the spatially perturbed chemical gradients around obstacles. It is thus unlikely that they have developed specialized mechanisms to cope with environments having low to moderate concentrations of obstacles
DESI Survey Validation Spectra Reveal an Increasing Fraction of Recently Quenched Galaxies at
We utilize bright Luminous Red Galaxies (LRGs) from the novel
Dark Energy Spectroscopic Instrument Survey Validation spectroscopic sample,
leveraging its deep ( hour/galaxy exposure time) spectra to
characterize the contribution of recently quenched galaxies to the massive
galaxy population at . We use Prospector to infer non-parametric
star formation histories and identify a significant population of
post-starburst galaxies that have joined the quiescent population within the
past Gyr. The highest redshift subset (277 at ) of our sample of
recently quenched galaxies represents the largest spectroscopic sample of
post-starburst galaxies at that epoch. At , we measure the number
density of quiescent LRGs, finding that recently quenched galaxies constitute a
growing fraction of the massive galaxy population with increasing lookback
time. Finally, we quantify the importance of this population amongst massive
() LRGs by measuring the fraction of
stellar mass each galaxy formed in the Gyr before observation, . Although galaxies with are rare at
( of the population), by they constitute
of massive galaxies. Relaxing this threshold, we find that galaxies with
constitute of the massive galaxy population
at . We also identify a small but significant sample of galaxies at
that formed with , implying that they may
be analogues to high-redshift quiescent galaxies that formed on similar
timescales. Future analysis of this unprecedented sample promises to illuminate
the physical mechanisms that drive the quenching of massive galaxies after
cosmic noon.Comment: Submitted to ApJ Letters after DESI Collaboration Review. 14 pages, 5
figures, comments welcome
The DESI One-Percent Survey: Evidence for Assembly Bias from Low-Redshift Counts-in-Cylinders Measurements
We explore the galaxy-halo connection information that is available in
low-redshift samples from the early data release of the Dark Energy
Spectroscopic Instrument (DESI). We model the halo occupation distribution
(HOD) from z=0.1-0.3 using Survey Validation 3 (SV3; a.k.a., the One-Percent
Survey) data of the DESI Bright Galaxy Survey (BGS). In addition to more
commonly used metrics, we incorporate counts-in-cylinders (CiC) measurements,
which drastically tighten HOD constraints. Our analysis is aided by the Python
package, galtab, which enables the rapid, precise prediction of CiC for any HOD
model available in halotools. This methodology allows our Markov chains to
converge with much fewer trial points, and enables even more drastic speedups
due to its GPU portability. Our HOD fits constrain characteristic halo masses
tightly and provide statistical evidence for assembly bias, especially at lower
luminosity thresholds: the HOD of central galaxies in samples with
limiting absolute magnitude and samples is
positively correlated with halo concentration with a significance of 99.9% and
99.5%, respectively. Our models also favor positive central assembly bias for
the brighter sample at (94.8% significance), but
there is no significant evidence for assembly bias with the same luminosity
threshold at . We provide our constraints for each threshold
sample's characteristic halo masses, assembly bias, and other HOD parameters.
These constraints are expected to be significantly tightened with future DESI
data, which will span an area 100 times larger than that of SV3
Local primordial non-Gaussianity from the large-scale clustering of photometric DESI luminous red galaxies
We use angular clustering of luminous red galaxies from the Dark Energy
Spectroscopic Instrument (DESI) imaging surveys to constrain the local
primordial non-Gaussianity parameter fNL. Our sample comprises over 12 million
targets, covering 14,000 square degrees of the sky, with redshifts in the range
0.2< z < 1.35. We identify Galactic extinction, survey depth, and astronomical
seeing as the primary sources of systematic error, and employ linear regression
and artificial neural networks to alleviate non-cosmological excess clustering
on large scales. Our methods are tested against log-normal simulations with and
without fNL and systematics, showing superior performance of the neural network
treatment in reducing remaining systematics. Assuming the universality
relation, we find fNL at 68\%(95\%) confidence.
With a more aggressive treatment, including regression against the full set of
imaging maps, our maximum likelihood value shifts slightly to fNL and
the uncertainty on fNL increases due to the removal of large-scale clustering
information. We apply a series of robustness tests (e.g., cuts on imaging,
declination, or scales used) that show consistency in the obtained constraints.
Despite extensive efforts to mitigate systematics, our measurements indicate
fNL > 0 with a 99.9 percent confidence level. This outcome raises concerns as
it could be attributed to unforeseen systematics, including calibration errors
or uncertainties associated with low-\ell systematics in the extinction
template. Alternatively, it could suggest a scale-dependent fNL model--causing
significant non-Gaussianity around large-scale structure while leaving cosmic
microwave background scales unaffected. Our results encourage further studies
of fNL with DESI spectroscopic samples, where the inclusion of 3D clustering
modes should help separate imaging systematics.Comment: 19 pages, 15 figures, 6 tables (Appendix excluded). Submitted to
MNRA
Associations between tamoxifen, estrogens, and FSH serum levels during steady state tamoxifen treatment of postmenopausal women with breast cancer
<p>Abstract</p> <p>Background</p> <p>The cytochrome P450 (CYP) enzymes 2C19, 2D6, and 3A5 are responsible for converting the selective estrogen receptor modulator (SERM), tamoxifen to its active metabolites 4-hydroxy-tamoxifen (4OHtam) and 4-hydroxy-<it>N</it>-demethyltamoxifen (4OHNDtam, endoxifen). Inter-individual variations of the activity of these enzymes due to polymorphisms may be predictors of outcome of breast cancer patients during tamoxifen treatment. Since tamoxifen and estrogens are both partly metabolized by these enzymes we hypothesize that a correlation between serum tamoxifen and estrogen levels exists, which in turn may interact with tamoxifen on treatment outcome. Here we examined relationships between the serum levels of tamoxifen, estrogens, follicle-stimulating hormone (FSH), and also determined the genotypes of CYP2C19, 2D6, 3A5, and SULT1A1 in 90 postmenopausal breast cancer patients.</p> <p>Methods</p> <p>Tamoxifen and its metabolites were measured by liquid chromatography-tandem mass spectrometry. Estrogen and FSH levels were determined using a sensitive radio- and chemiluminescent immunoassay, respectively.</p> <p>Results</p> <p>We observed significant correlations between the serum concentrations of tamoxifen, <it>N</it>-dedimethyltamoxifen, and tamoxifen-<it>N</it>-oxide and estrogens (p < 0.05). The genotype predicted CYP2C19 activity influenced the levels of both tamoxifen metabolites and E1.</p> <p>Conclusions</p> <p>We have shown an association between tamoxifen and its metabolites and estrogen serum levels. An impact of CYP2C19 predicted activity on tamoxifen, as well as estrogen kinetics may partly explain the observed association between tamoxifen and its metabolites and estrogen serum levels. Since the role of estrogen levels during tamoxifen therapy is still a matter of debate further prospective studies to examine the effect of tamoxifen and estrogen kinetics on treatment outcome are warranted.</p
A Review of the Urban Development and Transport Impacts on Public Health with Particular Reference to Australia: Trans-Disciplinary Research Teams and Some Research Gaps
Urbanization and transport have a direct effect on public health. A transdisciplinary approach is proposed and illustrated to tackle the general problem of these environmental stressors and public health. Processes driving urban development and environmental stressors are identified. Urbanization, transport and public health literature is reviewed and environmental stressors are classified into their impacts and which group is affected, the geographical scale and potential inventions. Climate change and health impacts are identified as a research theme. From an Australian perspective, further areas for research are identified
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