60 research outputs found
The PAU Survey: Photometric redshifts using transfer learning from simulations
In this paper we introduce the \textsc{Deepz} deep learning photometric
redshift (photo-) code. As a test case, we apply the code to the PAU survey
(PAUS) data in the COSMOS field. \textsc{Deepz} reduces the
scatter statistic by 50\% at compared to existing algorithms.
This improvement is achieved through various methods, including transfer
learning from simulations where the training set consists of simulations as
well as observations, which reduces the need for training data. The redshift
probability distribution is estimated with a mixture density network (MDN),
which produces accurate redshift distributions. Our code includes an
autoencoder to reduce noise and extract features from the galaxy SEDs. It also
benefits from combining multiple networks, which lowers the photo- scatter
by 10 percent. Furthermore, training with randomly constructed coadded fluxes
adds information about individual exposures, reducing the impact of photometric
outliers. In addition to opening up the route for higher redshift precision
with narrow bands, these machine learning techniques can also be valuable for
broad-band surveys.Comment: Accepted versio
The Physics of the Accelerating Universe Survey: narrow-band image photometry
PAUCam is an innovative optical narrow-band imager mounted at the William Herschel Telescope built for the Physics of the Accelerating Universe Survey (PAUS). Its set of 40 filters results in images that are complex to calibrate, with specific instrumental signatures that cannot be processed with traditional data reduction techniques. In this paper, we present two pipelines developed by the PAUS data management team with the objective of producing science-ready catalogues from the uncalibrated raw images. The NIGHTLY pipeline takes care of entire image processing, with bespoke algorithms for photometric calibration and scatter-light correction. The Multi-Epoch and Multi-Band Analysis pipeline performs forced photometry over a reference catalogue to optimize the photometric redshift (photo-z) performance. We verify against spectroscopic observations that the current approach delivers an inter-band photometric calibration of 0.8 perâcent across the 40 narrow-band set. The large volume of data produced every night and the rapid survey strategy feedback constraints require operating both pipelines in the Port dâInformaciĂł Cientifica data centre with intense parallelization. While alternative algorithms for further improvements in photo-z performance are under investigation, the image calibration and photometry presented in this work already enable state-of-the-art photo-z down to iAB = 23.0
The PAU Survey: Narrow-band image photometry
PAUCam is an innovative optical narrow-band imager mounted at the William
Herschel Telescope built for the Physics of the Accelerating Universe Survey
(PAUS). Its set of 40 filters results in images that are complex to calibrate,
with specific instrumental signatures that cannot be processed with traditional
data reduction techniques. In this paper we present two pipelines developed by
the PAUS data management team with the objective of producing science-ready
catalogues from the uncalibrated raw images. The Nightly pipeline takes care of
all image processing, with bespoke algorithms for photometric calibration and
scatter-light correction. The Multi-Epoch and Multi-Band Analysis (MEMBA)
pipeline performs forced photometry over a reference catalogue to optimize the
photometric redshift performance. We verify against spectroscopic observations
that the current approach delivers an inter-band photometric calibration of
0.8% across the 40 narrow-band set. The large volume of data produced every
night and the rapid survey strategy feedback constraints require operating both
pipelines in the Port d'Informaci\'o Cientifica data centre with intense
parallelization. While alternative algorithms for further improvements in
photo-z performance are under investigation, the image calibration and
photometry presented in this work already enable state-of-the-art photometric
redshifts down to iAB=23.0.Comment: 32 pages, 26 figures, MNRAS in pres
The PAU Survey: Photometric redshift estimation in deep wide fields
We present photometric redshifts (photo-) for the deep wide fields of the
Physics of the Accelerating Universe Survey (PAUS), covering an area of
50 deg, for 1.8 million objects up to .
The PAUS deep wide fields overlap with the W1 and W3 fields from CFHTLenS and
the G09 field from KiDS/GAMA. Photo- are estimated using the 40 narrow bands
(NB) of PAUS and the broad bands (BB) of CFHTLenS and KiDS. We compute the
redshifts with the SED template-fitting code BCNZ, with a modification in the
calibration technique of the zero-point between the observed and the modelled
fluxes, that removes any dependence on spectroscopic redshift samples. We
enhance the redshift accuracy by introducing an additional photo- estimate
(), obtained through the combination of the BCNZ and the
BB-only photo-. Comparing with spectroscopic redshifts estimates
(), we obtain a for all galaxies
with and a typical bias
smaller than 0.01. For we find , this is a factor of higher accuracy than the
corresponding BB-only results. We obtain similar performance when we split the
samples into red (passive) and blue (active) galaxies. We validate the redshift
probability obtained by BCNZ and compare its performance with that of
. These photo- catalogues will facilitate important science
cases, such as the study of galaxy clustering and intrinsic alignment at high
redshifts () and faint magnitudes.Comment: 24 pages, 26 figures, submitted to MNRA
The PAU Survey: a new constraint on galaxy formation models using the observed colour redshift relation
We use the GALFORM semi-analytical galaxy formation model implemented in the Planck Millennium N-body simulation to build a mock galaxy catalogue on an observerâs past lightcone. The mass resolution of this N-body simulation is almost an order of magnitude better than in previous simulations used for this purpose, allowing us to probe fainter galaxies and hence build a more complete mock catalogue at low redshifts. The high time cadence of the simulation outputs allows us to make improved calculations of galaxy properties and positions in the mock. We test the predictions of the mock against the Physics of the Accelerating Universe Survey, a narrow-band imaging survey with highly accurate and precise photometric redshifts, which probes the galaxy population over a lookback time of 8 billion years. We compare the model against the observed number counts, redshift distribution, and evolution of the observed colours and find good agreement; these statistics avoid the need for model-dependent processing of the observations. The model produces red and blue populations that have similar median colours to the observations. However, the bimodality of galaxy colours in the model is stronger than in the observations. This bimodality is reduced on including a simple model for errors in the GALFORM photometry. We examine how the model predictions for the observed galaxy colours change when perturbing key model parameters. This exercise shows that the median colours and relative abundance of red and blue galaxies provide constraints on the strength of the feedback driven by supernovae used in the model
The PAU Survey: a new constraint on galaxy formation models using the observed colour redshift relation
We use the GALFORM semi-analytical galaxy formation model implemented in the
Planck Millennium N-body simulation to build a mock galaxy catalogue on an
observer's past lightcone. The mass resolution of this N-body simulation is
almost an order of magnitude better than in previous simulations used for this
purpose, allowing us to probe fainter galaxies and hence build a more complete
mock catalogue at low redshifts. The high time cadence of the simulation
outputs allows us to make improved calculations of galaxy properties and
positions in the mock. We test the predictions of the mock against the Physics
of the Accelerating Universe Survey, a narrow band imaging survey with highly
accurate and precise photometric redshifts, which probes the galaxy population
over a lookback time of 8 billion years. We compare the model against the
observed number counts, redshift distribution and evolution of the observed
colours and find good agreement; these statistics avoid the need for
model-dependent processing of the observations. The model produces red and blue
populations that have similar median colours to the observations. However, the
bimodality of galaxy colours in the model is stronger than in the observations.
This bimodality is reduced on including a simple model for errors in the
GALFORM photometry. We examine how the model predictions for the observed
galaxy colours change when perturbing key model parameters. This exercise shows
that the median colours and relative abundance of red and blue galaxies provide
constraints on the strength of the feedback driven by supernovae used in the
model
Models of Neutrino Masses and Mixings
We review theoretical ideas, problems and implications of neutrino masses and
mixing angles. We give a general discussion of schemes with three light
neutrinos. Several specific examples are analyzed in some detail, particularly
those that can be embedded into grand unified theories.Comment: 44 pages, 2 figures, version accepted for publication on the Focus
Issue on 'Neutrino Physics' edited by F.Halzen, M.Lindner and A. Suzuki, to
be published in New Journal of Physics
Is staying overnight in a farming hut a risk factor for malaria infection in a setting with insecticide-treated bed nets in rural Laos?
<p>Abstract</p> <p>Background</p> <p>Overnight stays in farming huts are known to pose a risk of malaria infection. However, studies reporting the risk were conducted in the settings of poor net coverage. This study sought to assess whether an overnight stay in a farming hut is associated with an increased risk of malaria infection if insecticide-treated bed nets (ITNs) are properly used.</p> <p>Methods</p> <p>A pair of cross-sectional surveys was carried out in the Lamarm district of Sekong province, Laos, in March (dry season) and August (rainy season) in 2008. Questionnaire-based interviews and blood examinations were conducted with farmers and their household members from three randomly selected villages in March (127 households, 891 people) and August (128 households, 919 people). Logistic regression analysis, adjusted for potential confounding factors, was used to assess the association between malaria infection status and frequency of overnight stays for the two weeks prior to the study in both the seasons.</p> <p>Results</p> <p>In March, 13.7% of participants reported staying overnight in a farming hut at least once in the previous two weeks. The percentage increased to 74.6% in August. Not only adults but also young children stayed overnight as often as adults. The use of an ITN the preceding night was common both in farming huts (66.3% in March, 95.2% in August), and in main residences (85.8% in March, 92.5% in August). Logistic regression analysis showed no statistical association between malaria infection status and frequency of overnight stays in farming huts in either study period. However, people sharing one family type net with five people or more were significantly more likely to have malaria than those sharing a net with up to two people in the dry season.</p> <p>Conclusions</p> <p>This study showed that staying overnight in farming huts was not associated with an increased risk of malaria infection in the setting where ITNs were widely used in farming huts. It suggests that malaria infection during overnight stays in farming huts might be preventable if ITNs are properly used in rural Laos.</p
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