812 research outputs found
Subaru Weak Lensing survey -- II: Multi-object Spectroscopy and Cluster Masses
We present the first results of a MOS campaign to follow up cluster
candidates located via weak lensing. Our main goals are to search for spatial
concentrations of galaxies that are plausible optical counterparts of the weak
lensing signals, and to determine the cluster redshifts from those of member
galaxies. Around each of 36 targeted cluster candidates, we obtain 15-32 galaxy
redshifts. For 28 of these targets, we confirm a secure cluster identification.
This includes three cases where two clusters at different redshifts are
projected along the same line-of-sight. In 6 of the 8 unconfirmed targets, we
find multiple small galaxy concentrations at different redshifts. In both the
remaining two targets, a single small galaxy concentration is found. We
evaluate the weak lensing mass of confirmed clusters. For a subsample of our
most cleanly measured clusters, we investigate the statistical relation between
their weak lensing mass and the velocity dispersion of their member galaxies,
comparing our sample with optically and X-ray selected samples from the
literature. Our lensing-selected clusters are consistent with
sigma_v=sigma_sis, with a similar scatter to the optically and X-ray selected
clusters. We thus find no evidence of selection bias compared to these other
techniques. We also derive an empirical relation between the cluster mass and
the galaxy velocity dispersion, which is in reasonable agreement with the
prediction of N-body simulations in the LCDM cosmology.Comment: 58 pages, 45 figures, submitted to PASJ. A version with
full-resolution figures is available at
http://th.nao.ac.jp/~hamanatk/PP/supcam_wl2.pd
Joint cosmic shear measurements with the Keck and William Herschel Telescopes
The recent measurements of weak lensing by large-scale structure present significant new opportunities for studies of the matter distribution in the Universe. Here, we present a new cosmic shear survey carried out with the Echelle Spectrograph and Imager on the Keck II telescope. This covers a total of 0.6 square degrees in 173 fields probing independent lines of sight, hence minimizing the impact of sample variance. We also extend our measurements of cosmic shear with the William Herschel Telescope (Bacon, Refregier & Ellis 2000) to a survey area of 1 square degree. The joint measurements with two independent telescopes allow us to assess the impact of instrument-specific systematics, one of the major difficulties in cosmic shear measurements. For both surveys, we account for effects such as smearing by the point spread function and shearing due to telescope optics carefully. We find negligible residuals in both cases and recover mutually consistent cosmic shear signals, significant at the 5.1σ level. We present a simple method to compute the statistical error in the shear correlation function, including non-Gaussian sample variance and the covariance between different angular bins. We measure shear correlation functions for all fields and use these to ascertain the amplitude of the matter power spectrum, finding σ₈(Ω_m/0.3)^(0.68) = 0.97 ± 0.13 with 0.14 < Ω_m < 0.65 in a Λ cold dark matter (ΛCDM) model with Γ= 0.21. These 68 per cent confidence level uncertainties include sample variance, statistical noise, redshift uncertainty and the error in the shear measurement method. The results from our two independent surveys are both consistent with measurements of cosmic shear from other groups. We discuss how our results compare with current normalization from cluster abundance
Joint cosmic shear measurements with the Keck and William Herschel Telescopes
The recent measurements of weak lensing by large-scale structure present significant new opportunities for studies of the matter distribution in the Universe. Here, we present a new cosmic shear survey carried out with the Echelle Spectrograph and Imager on the Keck II telescope. This covers a total of 0.6 square degrees in 173 fields probing independent lines of sight, hence minimizing the impact of sample variance. We also extend our measurements of cosmic shear with the William Herschel Telescope (Bacon, Refregier & Ellis 2000) to a survey area of 1 square degree. The joint measurements with two independent telescopes allow us to assess the impact of instrument-specific systematics, one of the major difficulties in cosmic shear measurements. For both surveys, we account for effects such as smearing by the point spread function and shearing due to telescope optics carefully. We find negligible residuals in both cases and recover mutually consistent cosmic shear signals, significant at the 5.1σ level. We present a simple method to compute the statistical error in the shear correlation function, including non-Gaussian sample variance and the covariance between different angular bins. We measure shear correlation functions for all fields and use these to ascertain the amplitude of the matter power spectrum, finding σ₈(Ω_m/0.3)^(0.68) = 0.97 ± 0.13 with 0.14 < Ω_m < 0.65 in a Λ cold dark matter (ΛCDM) model with Γ= 0.21. These 68 per cent confidence level uncertainties include sample variance, statistical noise, redshift uncertainty and the error in the shear measurement method. The results from our two independent surveys are both consistent with measurements of cosmic shear from other groups. We discuss how our results compare with current normalization from cluster abundance
A Subaru Weak Lensing Survey I: Cluster Candidates and Spectroscopic Verification
We present the results of an ongoing weak lensing survey conducted with the
Subaru telescope whose initial goal is to locate and study the distribution of
shear-selected structures or halos. Using a Suprime-cam imaging survey spanning
21.82 square degree, we present a catalog of 100 candidate halos located from
lensing convergence maps. Our sample is reliably drawn from that subset of our
survey area, (totaling 16.72 square degree) uncontaminated by bright stars and
edge effects and limited at a convergence signal to noise ratio of 3.69. To
validate the sample detailed spectroscopic measures have been made for 26
candidates using the Subaru multi-object spectrograph, FOCAS. All are confirmed
as clusters of galaxies but two arise as the superposition of multiple clusters
viewed along the line of sight. Including data available in the literature and
an ongoing Keck spectroscopic campaign, a total of 41 halos now have reliable
redshifts. For one of our survey fields, the XMM LSS (Pierre et al. 2004)
field, we compare our lensing-selected halo catalog with its X-ray equivalent.
Of 15 halos detected in the XMM-LSS field, 10 match with published X-ray
selected clusters and a further 2 are newly-detected and spectroscopically
confirmed in this work. Although three halos have not yet been confirmed, the
high success rate within the XMM-LSS field (12/15) confirms that weak lensing
provides a reliable method for constructing cluster catalogs, irrespective of
the nature of the constituent galaxies or the intracluster medium.Comment: To appear in ApJ, High resolution preprint available at
http://anela.mtk.nao.ac.jp/suprime33/papers/p1.ps.g
The effects of charge transfer inefficiency (CTI) on galaxy shape measurements
(Abridged) We examine the effects of charge transfer inefficiency (CTI)
during CCD readout on galaxy shape measurements required by studies of weak
gravitational lensing. We simulate a CCD readout with CTI such as that caused
by charged particle radiation damage. We verify our simulations on data from
laboratory-irradiated CCDs. Only charge traps with time constants of the same
order as the time between row transfers during readout affect galaxy shape
measurements. We characterize the effects of CTI on various galaxy populations.
We baseline our study around p-channel CCDs that have been shown to have charge
transfer efficiency up to an order of magnitude better than several models of
n-channel CCDs designed for space applications. We predict that for galaxies
furthest from the readout registers, bias in the measurement of galaxy shapes,
Delta(e), will increase at a rate of 2.65 +/- 0.02 x 10^(-4) per year at L2 for
accumulated radiation exposure averaged over the solar cycle. If uncorrected,
this will consume the entire shape measurement error budget of a dark energy
mission within about 4 years. Software mitigation techniques demonstrated
elsewhere can reduce this by a factor of ~10, bringing the effect well below
mission requirements. CCDs with higher CTI than the ones we studeied may not
meet the requirements of future dark energy missions. We discuss ways in which
hardware could be designed to further minimize the impact of CTI.Comment: 11 pages, 6 figures, and 2 tables. Accepted for publication in PAS
Reverse Alignment - Understanding Centerline Measurement.
Tutorialpg. 189-196Shaft alignment is a key factor in reducing vibrations and increasing reliability in rotating equipment. The most popular method of measurement is "reverse alignment." This method is often considered so complicated that many users have developed step by step worksheets, plotting boards, programmable calculators, and computer-aided laser devices that can guide the aligner through the procedure without a real understanding of the fundamentals of alignment. A need for a good understanding of the reverse method of measurement prompted this presentation. The focus herein is to show how misalignment affects the rotor's behavior. Using a back to basics graphical method, it is shown how to visualize the shaft center lines that enable the aligner to use logic for the easiest and best move. Calculation of thermal growth and how to select an allowable tolerance is also discussed. Hot alignment is presented by showing different online monitoring systems as well as how to misalign cold so that the shafts will be colinear during operation. An alignment trainer is used to demonstrate how an actual alignment is made
Equatorial locations of water on Mars: Improved resolution maps based on Mars Odyssey Neutron Spectrometer data
We present a map of the near subsurface hydrogen distribution on Mars, based on epithermal neutron data from the Mars Odyssey Neutron Spectrometer. The map’s spatial resolution is approximately improved two-fold via a new form of the pixon image reconstruction technique. We discover hydrogen-rich mineralogy far from the poles, including ∼10 wt.% water equivalent hydrogen (WEH) on the flanks of the Tharsis Montes and >40 wt.% WEH at the Medusae Fossae Formation (MFF). The high WEH abundance at the MFF implies the presence of bulk water ice. This supports the hypothesis of recent periods of high orbital obliquity during which water ice was stable on the surface. We find the young undivided channel system material in southern Elysium Planitia to be distinct from its surroundings and exceptionally dry; there is no evidence of hydration at the location in Elysium Planitia suggested to contain a buried water ice sea. Finally, we find that the sites of recurring slope lineae (RSL) do not correlate with subsurface hydration. This implies that RSL are not fed by large, near-subsurface aquifers, but are instead the result of either small ( < 120 km diameter) aquifers, deliquescence of perchlorate and chlorate salts or dry, granular flows
Kinetic and structure–activity studies of the triazolium ion-catalysed benzoin condensation
Steady-state kinetic and structure–activity studies of a series of six triazolium-ion pre-catalysts 2a–2f were investigated for the benzoin condensation. These data provide quantitative insight into the role of triazolium N-aryl substitution under synthetically relevant catalytic conditions in a polar solvent environment. Kinetic behaviour was significantly different to that previously reported for a related thiazolium-ion pre-catalyst 1, with the observed levelling of initial rate constants to νmax at high aldehyde concentrations for all triazolium catalysts. Values for νmax for 2a–2f increase with electron withdrawing N-aryl substituents, in agreement with reported optimal synthetic outcomes under catalytic conditions, and vary by 75-fold across the series. The levelling of rate constants supports a change in rate-limiting step and evidence supports the assignment of the Breslow-intermediate forming step to the plateau region. Correlation of νmax reaction data yielded a positive Hammett ρ-value (ρ = +1.66) supporting the build up of electron density adjacent to the triazolium N-Ar in the rate-limiting step favoured by electron withdrawing N-aryl substituents. At lower concentrations of aldehyde, both Breslow-intermediate and benzoin formation are partially rate-limiting
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