1,874 research outputs found
The Hubble Constant determined through an inverse distance ladder including quasar time delays and Type Ia supernovae
Context. The precise determination of the present-day expansion rate of the
Universe, expressed through the Hubble constant , is one of the most
pressing challenges in modern cosmology. Assuming flat CDM,
inference at high redshift using cosmic-microwave-background data from Planck
disagrees at the 4.4 level with measurements based on the local
distance ladder made up of parallaxes, Cepheids and Type Ia supernovae (SNe
Ia), often referred to as "Hubble tension". Independent,
cosmological-model-insensitive ways to infer are of critical importance.
Aims. We apply an inverse-distance-ladder approach, combining strong-lensing
time-delay-distance measurements with SN Ia data. By themselves, SNe Ia are
merely good relative distance indicators, but by anchoring them to strong
gravitational lenses one can obtain an measurement that is relatively
insensitive to other cosmological parameters. Methods. A cosmological parameter
estimate is performed for different cosmological background models, both for
strong-lensing data alone and for the combined lensing + SNe Ia data sets.
Results. The cosmological-model dependence of strong-lensing measurements
is significantly mitigated through the inverse distance ladder. In combination
with SN Ia data, the inferred consistently lies around 73-74 km s
Mpc, regardless of the assumed cosmological background model. Our
results agree nicely with those from the local distance ladder, but there is a
>2 tension with Planck results, and a ~1.5 discrepancy with
results from an inverse distance ladder including Planck, Baryon Acoustic
Oscillations and SNe Ia. Future strong-lensing distance measurements will
reduce the uncertainties in from our inverse distance ladder.Comment: 5 pages, 3 figures, A&A letters accepted versio
The Rich Globular Cluster System of Abell 1689 and the Radial Dependence of the Globular Cluster Formation Efficiency
We study the rich globular cluster (GC) system in the center of the massive
cluster of galaxies Abell 1689 (z=0.18), one of the most powerful gravitational
lenses known. With 28 HST/ACS orbits in the F814W bandpass, we reach magnitude
I_814=29 with >90% completeness and sample the brightest ~5% of the GC system.
Assuming the well-known Gaussian form of the GC luminosity function (GCLF), we
estimate a total population of N(GC_total) = 162,850 GCs within a projected
radius of 400kpc. As many as half may comprise an intracluster component. Even
with the sizable uncertainties, which mainly result from the uncertain GCLF
parameters, this is by far the largest GC system studied to date. The specific
frequency S_N is high, but not uncommon for central galaxies in massive
clusters, rising from S_N~5 near the center to ~12 at large radii. Passive
galaxy fading would increase S_N by ~20% at z=0. We construct the radial mass
profiles of the GCs, stars, intracluster gas, and lensing-derived total mass,
and we compare the mass fractions as a function of radius. The estimated mass
in GCs, M(GC_total)=3.9x10^10 Msun, is comparable to ~80% of the total stellar
mass of the Milky Way. The shape of the GC mass profile appears intermediate
between those of the stellar light and total cluster mass. Despite the extreme
nature of this system, the ratios of the GC mass to the baryonic and total
masses, and thus the GC formation efficiency, are typical of those in other
rich clusters when comparing at the same physical radii. The GC formation
efficiency is not constant, but varies with radius, in a manner that appears
similar for different clusters; we speculate on the reasons for this similarity
in profile.Comment: 13 pages, 11 figures; accepted for publication in Ap
Galaxy-Mass Correlations on 10 Mpc Scales in the Deep Lens Survey
We examine the projected correlation of galaxies with mass from small scales
(<few hundred kpc) where individual dark matter halos dominate, out to 15 Mpc
where correlated large-scale structure dominates. We investigate these profiles
as a function of galaxy luminosity and redshift. Selecting 0.8 million galaxies
in the Deep Lens Survey, we use photometric redshifts and stacked weak
gravitational lensing shear tomography out to radial scales of 1 degree from
the centers of foreground galaxies. We detect correlated mass density from
multiple halos and large-scale structure at radii larger than the virial
radius, and find the first observational evidence for growth in the galaxy-mass
correlation on 10 Mpc scales with decreasing redshift and fixed range of
luminosity. For a fixed range of redshift, we find a scaling of projected halo
mass with rest-frame luminosity similar to previous studies at lower redshift.
We control systematic errors in shape measurement and photometric redshift,
enforce volume completeness through absolute magnitude cuts, and explore
residual sample selection effects via simulations.Comment: 13 pages, 9 figures, re-submitted to ApJ after addressing referee
comment
Scaling Relations and Overabundance of Massive Clusters at z>~1 from Weak-Lensing Studies with HST
We present weak gravitational lensing analysis of 22 high-redshift (z >~1)
clusters based on Hubble Space Telescope images. Most clusters in our sample
provide significant lensing signals and are well detected in their
reconstructed two-dimensional mass maps. Combining the current results and our
previous weak-lensing studies of five other high-z clusters, we compare
gravitational lensing masses of these clusters with other observables. We
revisit the question whether the presence of the most massive clusters in our
sample is in tension with the current LambdaCDM structure formation paradigm.
We find that the lensing masses are tightly correlated with the gas
temperatures and establish, for the first time, the lensing mass-temperature
relation at z >~ 1. For the power law slope of the M-TX relation (M propto
T^{\alpha}), we obtain \alpha=1.54 +/- 0.23. This is consistent with the
theoretical self-similar prediction \alpha=3/2 and with the results previously
reported in the literature for much lower redshift samples. However, our
normalization is lower than the previous results by 20-30%, indicating that the
normalization in the M-TX relation might evolve. After correcting for Eddington
bias and updating the discovery area with a more conservative choice, we find
that the existence of the most massive clusters in our sample still provides a
tension with the current Lambda CDM model. The combined probability of finding
the four most massive clusters in this sample after marginalization over
current cosmological parameters is less than 1%.Comment: ApJ in press. See http://www.supernova.lbl.gov for additional
information pertaining to the HST Cluster SN Surve
Muscle plasticity related to changes in tubulin and αB-crystallin levels induced by eccentric contraction in rat skeletal muscles
We used the model of eccentric contraction of the hindlimb muscle by Ochi et al. to examine the role of eccentric contraction in muscle plasticity. This model aims to focus on stimulated skeletal muscle responses by measuring tissue weights and tracing the quantities of αB-crystallin and tubulin. The medial gastrocnemius muscle (GCM) responded to electrically induced eccentric contraction (EIEC) with significant increases in tissue weight (pâ<â0.01) and the ratio of tissue weight to body weight (pâ<â0.05); however, there was a decrease in soleus muscle weight after EIEC. EIEC in the GCM caused contractile-induced sustenance of the traced proteins, but the soleus muscle exhibited a remarkable decrease in α-tubulin and a 19% decrease in αB-crystallin. EIEC caused fast-to-slow myosin heavy chain (MHC) isoform type-oriented shift within both the GCM and soleus muscle. These results have shown that different MHC isoform type-expressing slow and fast muscles commonly undergo fast-to-slow type MHC isoform transformation. This suggests that different levels of EIEC affected each of the slow and fast muscles to induce different quantitative changes in the expression of αB-crystallin and α-tubulin
Dependence Of Binary Encounter Electron Production On The Charge State Of The Recoil Ion
We study the dependence of the production of binary encounter electrons on the charge state of recoil ions for 2.4 MeV u-l Xe21+ on He and Ar. Doubly differential cross sections of electron emission are calculated with the ncrMC method. We find that the contributions to the binary electron cross section from various recoil ion charge states reach a maximum near Ar5+ for the Ar target. In the case of the He target; double ionization dominates over single ionization for alt ejected electron energies above 100 eV. However, an unexpected local drop of double ionization in the binary peak region has been observed. This decrease is found to be related to a two-step, sequential removal of the two electrons. © 1993 IOP Publishing Ltd
Relative dosimetry using active matrix flatĂą panel imager (AMFPI) technology
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135008/1/mp8649.pd
Spurious Shear in Weak Lensing with LSST
The complete 10-year survey from the Large Synoptic Survey Telescope (LSST)
will image 20,000 square degrees of sky in six filter bands every few
nights, bringing the final survey depth to , with over 4 billion
well measured galaxies. To take full advantage of this unprecedented
statistical power, the systematic errors associated with weak lensing
measurements need to be controlled to a level similar to the statistical
errors.
This work is the first attempt to quantitatively estimate the absolute level
and statistical properties of the systematic errors on weak lensing shear
measurements due to the most important physical effects in the LSST system via
high fidelity ray-tracing simulations. We identify and isolate the different
sources of algorithm-independent, \textit{additive} systematic errors on shear
measurements for LSST and predict their impact on the final cosmic shear
measurements using conventional weak lensing analysis techniques. We find that
the main source of the errors comes from an inability to adequately
characterise the atmospheric point spread function (PSF) due to its high
frequency spatial variation on angular scales smaller than in the
single short exposures, which propagates into a spurious shear correlation
function at the -- level on these scales. With the large
multi-epoch dataset that will be acquired by LSST, the stochastic errors
average out, bringing the final spurious shear correlation function to a level
very close to the statistical errors. Our results imply that the cosmological
constraints from LSST will not be severely limited by these
algorithm-independent, additive systematic effects.Comment: 22 pages, 12 figures, accepted by MNRA
Deep VLA Observations of the Cluster 1RXS J0603.3+4214 in the Frequency Range of 1â2 GHz
We report L-band VLA observations of 1RXS J0603.3+4214, a cluster that hosts
a bright radio relic, known as the Toothbrush, and an elongated giant radio
halo. These new observations allow us to study the surface brightness
distribution down to one arcsec resolution with very high sensitivity. Our
images provide an unprecedented detailed view of the Toothbrush, revealing
enigmatic filamentary structures. To study the spectral index distribution, we
complement our analysis with published LOFAR and GMRT observations. The bright
`brush' of the Toothbrush shows a prominent narrow ridge to its north with a
sharp outer edge. The spectral index at the ridge is in the range
. We suggest that the ridge is caused by projection
along the line of sight. With a simple toy model for the smallest region of the
ridge, we conclude that the magnetic field is below and varies
significantly across the shock front. Our model indicates that the actual Mach
number is higher than that obtained from the injection index and agrees well
with the one derived from the overall spectrum, namely . The radio halo shows an average spectral index of
and a slight gradient from north to south. The
southernmost part of the halo is steeper and possibly related to a shock front.
Excluding the southernmost part, the halo morphology agrees very well with the
X-ray morphology. A power-law correlation is found between the radio and X-ray
surface brightnessComment: 23 pages, 21 figures, accepted for publication in Ap
Diffraction In The Binary Encounter Electron Peak Observed In Collisions Of 0.6 MeV Amuâ»Âč I7+, I23+ And Au11+ Projectiles With He And Ar
Relative double differential cross sections for electron emission from collisions of 0.6 MeV amu-1I7+and I23+ projectiles with Ar and Au11+projectiles with He were measured for electron energies from 100 eV to 2000 eV and for angles from 0° to 50°. Experimentally observed sudden shifts of the position of the binary encounter peak were interpreted as resulting from quantum interference in the scattering of target electrons from the partially stripped projectile ion. To this end calculations for the elastic scattering of free electrons initially at rest in the laboratory reference frame from the screened projectile field as well as model calculations of binary encounter electron production taking into account the target Compton profile were performed and compared with the experimental results. Good agreement was obtained for the angular locations of these shifts as well as for the angular distribution of the binary encounter electron yield. © 1992 IOP Publishing Ltd
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