201 research outputs found
Streamlined Calibrations of the ATLAS Precision Muon Chambers for Initial LHC Running
The ATLAS Muon Spectrometer is designed to measure the momentum of muons with
a resolution of dp/p = 3% and 10% at 100 GeV and 1 TeV momentum respectively.
For this task, the spectrometer employs 355,000 Monitored Drift Tubes (MDTs)
arrayed in 1200 Chambers. Calibration (RT) functions convert drift time
measurements into tube-centered impact parameters for track segment
reconstruction. RT functions depend on MDT environmental parameters and so must
be appropriately calibrated for local chamber conditions. We report on the
creation and application of a gas monitor system based calibration program for
muon track reconstruction in the LHC startup phase.Comment: 25 pages, 21 figure
Construction of Precision sMDT Detector for ATLAS Muon Spectrometer Upgrade
This paper describes the small-diameter monitored drift-tube detector
construction at the University of Michigan as a contribution to the ATLAS Muon
Spectrometer upgrade for the high-luminosity Large Hadron Collider at CERN.
Measurements of the first 30 chambers built at Michigan show that the drift
tube wire position accuracy meets the specification of 20 microns. The
positions of the platforms for alignment and magnetic field sensors are all
installed well within the required precision. The cosmic ray test measurements
show single wire tracking resolution of 100 +- 7 microns with an average
detection efficiency above 99 %. The infrastructure, tooling, techniques, and
procedures for chamber production are described in detail. The results from the
chamber quality control tests of the first 30 constructed chambers are
reported.Comment: 35 pages, 41 figure
Dark Energy Survey Year 6 Results: Intra-Cluster Light from Redshift 0.2 to 0.5
Using the full six years of imaging data from the Dark Energy Survey, we
study the surface brightness profiles of galaxy cluster central galaxies and
intra-cluster light. We apply a ``stacking'' method to over four thousand
galaxy clusters identified by the redMaPPer cluster finding algorithm in the
redshift range of 0.2 to 0.5. This yields high signal-to-noise radial profile
measurements of the central galaxy and intra-cluster light out to 1 Mpc from
the cluster center. Using redMaPPer richness as a cluster mass indicator, we
find that the intra-cluster light brightness has a strong mass dependence
throughout the 0.2 to 0.5 redshift range, and the dependence grows stronger at
a larger radius. In terms of redshift evolution, we find some evidence that the
central galaxy, as well as the diffuse light within the transition region
between the cluster central galaxy and intra-cluster light within 80 kpc from
the center, may be growing over time. At larger radii, more than 80 kpc away
from the cluster center, we do not find evidence of additional redshift
evolution beyond the cluster mass dependence, which is consistent with the
findings from the IllustrisTNG hydrodynamic simulation. We speculate that the
major driver of intra-cluster light growth, especially at large radii, is
associated with cluster mass growth. Finally, we find that the color of the
cluster central galaxy and intra-cluster light displays a radial gradient that
becomes bluer at a larger radius, which is consistent with a stellar stripping
and disruption origin of intra-cluster light as suggested by simulation
studies.Comment: Submitted to MNRA
Chemical Analysis of the Brightest Star of the Cetus II Ultra-Faint Dwarf Galaxy Candidate
We present a detailed chemical abundance analysis of the brightest star in
the ultra-faint dwarf (UFD) galaxy candidate Cetus II from high-resolution
Magellan/MIKE spectra. For this star, DES J011740.53-173053, abundances or
upper limits of 18 elements from Carbon to Europium are derived. Its chemical
abundances generally follow those of other UFD galaxy stars, with a slight
enhancement of the alpha-elements (Mg, Si, and Ca) and low neutron-capture
element (Sr, Ba, Eu) abundances supporting the classification of Cetus II as a
likely UFD. The star exhibits lower Sc, Ti, and V abundances than Milky Way
(MW) halo stars with similar metallicity. This signature is consistent with
yields from a supernova (SN) originating from a star with a mass of ~11.2 solar
masses. In addition, the star has a Potassium abundance of [K/Fe] = 0.81 which
is somewhat higher than the K abundances of MW halo stars with similar
metallicity, a signature which is also present in a number of UFD galaxies. A
comparison including globular clusters (GC) and stellar stream stars suggests
that high K is a specific characteristic for some UFD galaxy stars and can thus
be used to help classify objects as UFD galaxies.Comment: 15 pages, 7 figures, 5 tables, accepted to Ap
The MADPSZ catalogue of Planck clusters over the DES region: extending to lower mass and higher redshift
We present the first systematic follow-up of Planck Sunyaev-Zeldovich effect
(SZE) selected candidates down to signal-to-noise (S/N) of 3 over the 5000
deg covered by the Dark Energy Survey. Using the MCMF cluster confirmation
algorithm, we identify optical counterparts, determine photometric redshifts
and richnesses and assign a parameter, , that reflects the
probability that each SZE-optical pairing represents a real cluster rather than
a random superposition of physically unassociated systems. The new MADPSZ
cluster catalogue consists of 1092 MCMF confirmed clusters and has a purity of
85%. We present the properties of subsamples of the MADPSZ catalogue that have
purities ranging from 90% to 97.5%, depending on the adopted
threshold. halo mass estimates, redshifts, richnesses, and optical
centers are presented for all MADPSZ clusters. The MADPSZ catalogue adds 828
previously unknown Planck identified clusters over the DES footprint and
provides redshifts for an additional 50 previously published Planck selected
clusters with S/N>4.5. Using the subsample with spectroscopic redshifts, we
demonstrate excellent cluster photo- performance with an RMS scatter in
of 0.47%. Our MCMF based analysis allows us to infer the
contamination fraction of the initial S/N>3 Planck selected candidate list,
which is 50%. We present a method of estimating the completeness of the MADPSZ
cluster sample and selected subsamples. In comparison to the
previously published Planck cluster catalogues. this new S/N 3 MCMF
confirmed cluster catalogue populates the lower mass regime at all redshifts
and includes clusters up to z1.3.Comment: 20 pages, 5 Appendices, 17 figures, submitted to MNRA
Concerning Colour: The Effect of Environment on Type Ia Supernova Colour in the Dark Energy Survey
Recent analyses have found intriguing correlations between the colour ()
of type Ia supernovae (SNe Ia) and the size of their mass-step, the
relationship between host galaxy stellar mass and Hubble residual. These
analyses suggest that the underlying cause of this relationship is dust. Using
a sample of 675 photometrically-classified SNe Ia from the Dark Energy Survey
5-year sample, we study the differences in Hubble residual for a variety of
host and local properties for subsamples split by their colour (). We find a
difference for the size of the mass-step when comparing blue () and red () SNe. We observe the lowest r.m.s. scatter ()
in Hubble residual for blue SNe in low mass or blue environments, suggesting
that these objects provide the most homogeneous sample for cosmological
analyses. By fitting for -dependent relationships between Hubble residuals
and , approximating existing dust models, we remove the
mass-step from the data but find significant remaining steps in rest-frame
, indicating that current dust modelling based on may
not fully explain the remaining dispersion in SN luminosity. The most
dispersion is removed by instead accounting for a -dependent relationship
between Hubble residuals and global , resulting in
remaining steps in other environmental properties, suggesting that
provides different information about the environment of SNe Ia to
. This -dependent relation implies that may
be more closely linked to dust, motivating the future inclusion of galaxy
colour in the correction for SN distance biases.Comment: 18 pages, 8 figures. Submitted to MNRA
The Dark Energy Survey Supernova Program: Corrections on Photometry Due to Wavelength-dependent Atmospheric Effects
Wavelength-dependent atmospheric effects impact photometric supernova flux measurements for ground-based observations. We present corrections on supernova flux measurements from the Dark Energy Survey Supernova Programâs 5YR sample (DES-SN5YR) for differential chromatic refraction (DCR) and wavelength-dependent seeing, and we show their impact on the cosmological parameters w and Ωm . We use g â i colors of Type Ia supernovae to quantify astrometric offsets caused by DCR and simulate point-spread functions (PSFs) using the GalSIM package to predict the shapes of the PSFs with DCR and wavelength-dependent seeing. We calculate the magnitude corrections and apply them to the magnitudes computed by the DES-SN5YR photometric pipeline. We find that for the DES-SN5YR analysis, not accounting for the astrometric offsets and changes in the PSF shape cause an average bias of +0.2 mmag and â0.3 mmag, respectively, with standard deviations of 0.7 mmag and 2.7 mmag across all DES observing bands (griz) throughout all redshifts. When the DCR and seeing effects are not accounted for, we find that w and Ωm are lower by less than 0.004 ± 0.02 and 0.001 ± 0.01, respectively, with 0.02 and 0.01 being the 1Ï statistical uncertainties. Although we find that these biases do not limit the constraints of the DES-SN5YR sample, future surveys with much higher statistics, lower systematics, and especially those that observe in the u band will require these corrections as wavelength-dependent atmospheric effects are larger at shorter wavelengths. We also discuss limitations of our method and how they can be better accounted for in future surveys
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