11 research outputs found
Probing the Relation Between X-ray-Derived and Weak-Lensing-Derived Masses for Shear-Selected Galaxy Clusters: I. A781
We compare X-ray and weak-lensing masses for four galaxy clusters that
comprise the top-ranked shear-selected cluster system in the Deep Lens Survey.
The weak-lensing observations of this system, which is associated with A781,
are from the Kitt Peak Mayall 4-m telescope, and the X-ray observations are
from both Chandra and XMM-Newton. For a faithful comparison of masses, we adopt
the same matter density profile for each method, which we choose to be an NFW
profile. Since neither the X-ray nor weak-lensing data are deep enough to well
constrain both the NFW scale radius and central density, we estimate the scale
radius using a fitting function for the concentration derived from cosmological
hydrodynamic simulations and an X-ray estimate of the mass assuming
isothermality. We keep this scale radius in common for both X-ray and
weak-lensing profiles, and fit for the central density, which scales linearly
with mass. We find that for three of these clusters, there is agreement between
X-ray and weak-lensing NFW central densities, and thus masses. For the other
cluster, the X-ray central density is higher than that from weak-lensing by 2
sigma. X-ray images suggest that this cluster may be undergoing a merger with a
smaller cluster. This work serves as an additional step towards understanding
the possible biases in X-ray and weak-lensing cluster mass estimation methods.
Such understanding is vital to efforts to constrain cosmology using X-ray or
weak-lensing cluster surveys to trace the growth of structure over cosmic time.Comment: 14 pages, 7 figures, matches version in Ap
Exploring Large-scale Structure with Billions of Galaxies
We consider cosmological applications of galaxy number density correlations
to be inferred from future deep and wide multi-band optical surveys. We mostly
focus on very large scales as a probe of possible features in the primordial
power spectrum. We find the proposed survey of the Large Synoptic Survey
Telescope may be competitive with future all-sky CMB experiments over a broad
range of scales. On very large scales the inferred power spectrum is robust to
photometric redshift errors, and, given a sufficient number density of
galaxies, to angular variations in dust extinction and photometric calibration
errors. We also consider other applications, such as constraining dark energy
with the two CMB-calibrated standard rulers in the matter power spectrum, and
controlling the effect of photometric redshift errors to facilitate the
interpretation of cosmic shear data. We find that deep photometric surveys over
wide area can provide constraints that are competitive with spectroscopic
surveys in small volumes.Comment: 11 pages, 7 figures, ApJ accepted, references added, expanded
discussion in Sec. 3.
Science Frontiers In Galaxy Evolution: Deep-Wide Surveys
Astro2010: The Astronomy and Astrophysics Decadal Survey : Science White Papers no 79. Available online : http://www8.nationalacademies.org/astro2010/DetailFileDisplay.aspx?id=24
Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304 in May 1994. I. The Ground-Based Campaign
Optical, near-infrared, and radio observations of the BL Lac object
PKS2155-304 were obtained simultaneously with a continuous UV/EUV/X-ray
monitoring campaign in 1994 May. Further optical observations were gathered
throughout most of 1994. The radio, millimeter, and near-infrared data show no
strong correlations with the higher energies. The optical light curves exhibit
flickering of 0.2-0.3 mag on timescales of 1-2 days, superimposed on longer
timescale variations. Rapid variations of ~0.01 mag/min, which, if real, are
the fastest seen to date for any BL Lac object. Small (0.2-0.3 mag) increases
in the V and R bands occur simultaneously with a flare seen at higher energies.
All optical wavebands (UBVRI) track each other well over the period of
observation with no detectable delay. For most of the period the average colors
remain relatively constant, although there is a tendency for the colors (in
particular B-V) to vary more when the source fades. In polarized light, PKS
2155-304 showed strong color dependence and the highest optical polarization (U
= 14.3%) ever observed for this source. The polarization variations trace the
flares seen in the ultraviolet flux.Comment: 45 pages, latex file with encapsulated postscript, accepted to the
Astrophysical Journa
Monkeying Around in Mechanics: Using Student-Student Dialogue Videos to Increase Physics Learning
Variation in Dube3a expression affects neurotransmission at the Drosophila neuromuscular junction
Changes in UBE3A expression levels in neurons can cause neurogenetic disorders ranging from Angelman syndrome (AS) (decreased levels) to autism (increased levels). Here we investigated the effects on neuronal function of varying UBE3A levels using the Drosophila neuromuscular junction as a model for both of these neurogenetic disorders. Stimulations that evoked excitatory junction potentials (EJPs) at 1 Hz intermittently failed to evoke EJPs at 15 Hz in a significantly higher proportion of Dube3a over-expressors using the pan neuronal GAL4 driver C155-GAL4 (C155-GAL4>UAS-Dube3a) relative to controls (C155>+ alone). However, in the Dube3a over-expressing larval neurons with no failures, there was no difference in EJP amplitude at the beginning of the train, or the rate of decrease in EJP amplitude over the course of the train compared to controls. In the absence of tetrodotoxin (TTX), spontaneous EJPs were observed in significantly more C155-GAL4>UAS-Dube3a larva compared to controls. In the presence of TTX, spontaneous and evoked EJPs were completely blocked and mEJP amplitude and frequency did not differ among genotypes. These data suggest that over-expression of wild type Dube3a, but not a ubiquitination defective Dube3a-C/A protein, compromises the ability of motor neuron axons to support closely spaced trains of action potentials, while at the same time increasing excitability. EJPs evoked at 15 Hz in the absence of Dube3a (Dube3a15b homozygous mutant larvae) decayed more rapidly over the course of 30 stimulations compared to w1118 controls, and Dube3a15b larval muscles had significantly more negative resting membrane potentials (RMP). However, these results could not be recapitulated using RNAi knockdown of Dube3a in muscle or neurons alone, suggesting more global developmental defects contribute to this phenotype. These data suggest that reduced UBE3A expression levels may cause global changes that affect RMP and neurotransmitter release from motorneurons at the neuromuscular junction. Similar affects of under- and over-expression of UBE3A on membrane potential and synaptic transmission may underlie the synaptic plasticity defects observed in both AS and autism