4,095 research outputs found
The PEP survey: clustering of infrared-selected galaxies and structure formation at z~2 in the GOODS South
ABRIDGED-This paper presents the first direct estimate of the 3D clustering
properties of far-infrared sources up to z~3. This has been possible thanks to
the Pacs Evolutionary Probe (PEP) survey of the GOODS South field performed
with the PACS instrument onboard the Herschel Satellite. An analysis of the
two-point correlation function over the whole redshift range spanned by the
data reports for the correlation length, r_0~6.3 Mpc and r_0~6.7 Mpc,
respectively at 100um and 160um, corresponding to dark matter halo masses
M>~10^{12.4} M_sun. Objects at z~2 instead seem to be more strongly clustered,
with r_0~19 Mpc and r_0~17 Mpc in the two considered PACS channels. This
dramatic increase of the correlation length between z~1 and z~2 is connected
with the presence of a wide, M>~10^{14} M_sun, filamentary structure which
includes more than 50% of the sources detected at z~2. An investigation of the
properties of such sources indicates the possibility for boosted star-forming
activity in those which reside within the overdense environment with respect of
more isolated galaxies found in the same redshift range. Lastly, we also
present our results on the evolution of the relationship between luminous and
dark matter in star-forming galaxies between z~1 and z~2. We find that the
increase of (average) stellar mass in galaxies between z~1 and z~2 is
about a factor 10 lower than that of the dark matter haloes hosting such
objects ([z~1]/[z~2] ~ 0.4 vs M_{halo}[z~1]/M_{halo}[z~2] ~ 0.04). Our
findings agree with the evolutionary picture of downsizing whereby massive
galaxies at z~2 were more actively forming stars than their z~1 counterparts,
while at the same time contained a lower fraction of their mass in the form of
luminous matter.Comment: 14 pages, 8 figures, MNRAS accepte
Forward Global Photometric Calibration of the Dark Energy Survey
Many scientific goals for the Dark Energy Survey (DES) require calibration of
optical/NIR broadband photometry that is stable in time and uniform
over the celestial sky to one percent or better. It is also necessary to limit
to similar accuracy systematic uncertainty in the calibrated broadband
magnitudes due to uncertainty in the spectrum of the source. Here we present a
"Forward Global Calibration Method (FGCM)" for photometric calibration of the
DES, and we present results of its application to the first three years of the
survey (Y3A1). The FGCM combines data taken with auxiliary instrumentation at
the observatory with data from the broad-band survey imaging itself and models
of the instrument and atmosphere to estimate the spatial- and time-dependence
of the passbands of individual DES survey exposures. "Standard" passbands are
chosen that are typical of the passbands encountered during the survey. The
passband of any individual observation is combined with an estimate of the
source spectral shape to yield a magnitude in the standard
system. This "chromatic correction" to the standard system is necessary to
achieve sub-percent calibrations. The FGCM achieves reproducible and stable
photometric calibration of standard magnitudes of stellar
sources over the multi-year Y3A1 data sample with residual random calibration
errors of per exposure. The accuracy of the
calibration is uniform across the DES footprint to
within . The systematic uncertainties of magnitudes in
the standard system due to the spectra of sources are less than
for main sequence stars with .Comment: 25 pages, submitted to A
Photometric redshifts and clustering of emission line galaxies selected jointly by DES and eBOSS
We present the results of the first test plates of the extended Baryon
Oscillation Spectroscopic Survey. This paper focuses on the emission line
galaxies (ELG) population targetted from the Dark Energy Survey (DES)
photometry. We analyse the success rate, efficiency, redshift distribution, and
clustering properties of the targets. From the 9000 spectroscopic redshifts
targetted, 4600 have been selected from the DES photometry. The total success
rate for redshifts between 0.6 and 1.2 is 71\% and 68\% respectively for a
bright and faint, on average more distant, samples including redshifts measured
from a single strong emission line. We find a mean redshift of 0.8 and 0.87,
with 15 and 13\% of unknown redshifts respectively for the bright and faint
samples. In the redshift range 0.6<z<1.2, for the most secure spectroscopic
redshifts, the mean redshift for the bright and faint sample is 0.85 and 0.9
respectively. Star contamination is lower than 2\%. We measure a galaxy bias
averaged on scales of 1 and 10~Mpc/h of 1.72 \pm 0.1 for the bright sample and
of 1.78 \pm 0.12 for the faint sample. The error on the galaxy bias have been
obtained propagating the errors in the correlation function to the fitted
parameters. This redshift evolution for the galaxy bias is in agreement with
theoretical expectations for a galaxy population with MB-5\log h < -21.0. We
note that biasing is derived from the galaxy clustering relative to a model for
the mass fluctuations. We investigate the quality of the DES photometric
redshifts and find that the outlier fraction can be reduced using a comparison
between template fitting and neural network, or using a random forest
algorithm
Exploratory 7-Tesla magnetic resonance spectroscopy in Huntington’s disease provides in vivo evidence for impaired energy metabolism
Huntington’s disease (HD) is a neurodegenerative genetic disorder that affects the brain. Atrophy of deep grey matter structures has been reported and it is likely that underlying pathologic processes occur before, or in concurrence with, volumetric changes. Measurement of metabolite concentrations in these brain structures has the potential to provide insight into pathological processes. We aim to gain understanding of metabolite changes with respect to the disease stage and pathophysiological changes. We studied five brain regions using magnetic resonance spectroscopy (MRS) using a 7-Tesla MRI scanner. Localized proton spectra were acquired to obtain six metabolite concentrations. MRS was performed in the caudate nucleus, putamen, thalamus, hypothalamus, and frontal lobe in 44 control subjects, premanifest gene carriers and manifest HD. In the caudate nucleus, HD patients display lower NAA (p = 0.009) and lower creatine concentration (p = 0.001) as compared to controls. In the putamen, manifest HD patients show lower NAA (p = 0.024), lower creatine concentration (p = 0.027), and lower glutamate (p = 0.013). Although absolute values of NAA, creatine, and glutamate were lower, no significant differences to controls were found in the premanifest gene carriers. The lower concentrations of NAA and creatine in the caudate nucleus and putamen of early manifest HD suggest deficits in neuronal integrity and energy metabolism. The changes in glutamate could support the excitotoxicity theory. These findings not only give insight into neuropathological changes in HD but also indicate that MRS can possibly be applied in future clinical trails to evaluate medication targeted at specific metabolic processes
- …