168 research outputs found
An In Situ Study of the Role of Pressure on Fe Recrystallization and Grain Growth during Thermomechanical Processing
Elevated pressures are encountered in many metal forming processes that can
alter microstructural evolution rates. Here we measure rate changes with
pressure in recrystallization and grain growth in Fe through adaptation of
synchrotron-compatible multi-anvil presses, originally designed for study of
the mantle. Recrystallization and grain growth are monitored in situ using
high-energy X-ray diffraction. Principal component analysis applied to the
diffraction images is used to quantify evolution rates, with increasing
pressure significantly slowing the process
Star Formation at z=2.481 in the Lensed Galaxy SDSS J1110+6459, I: Lens Modeling and Source Reconstruction
Using the combined resolving power of the Hubble Space Telescope and
gravitational lensing, we resolve star-forming structures in a z~2.5 galaxy on
scales much smaller than the usual kiloparsec diffraction limit of HST. SGAS
J111020.0+645950.8 is a clumpy, star forming galaxy lensed by the galaxy
cluster SDSS J1110+6459 at z = 0.659, with a total magnification ~30x across
the entire arc. We use a hybrid parametric/non-parametric strong lensing mass
model to compute the deflection and magnification of this giant arc,
reconstruct the light distribution of the lensed galaxy in the source plane,
and resolve the star formation into two dozen clumps. We develop a
forward-modeling technique to model each clump in the source plane. We ray
trace the model to the image plane, convolve with the instrumental point spread
function (PSF), and compare with the GALFIT model of the clumps in the image
plane, which decomposes clump structure from more extended emission. This
technique has the advantage, over ray tracing, by accounting for the asymmetric
lensing shear of the galaxy in the image plane and the instrument PSF. At this
resolution, we can begin to study star formation on a clump-by-clump basis,
toward the goal of understanding feedback mechanisms and the buildup of
exponential disks at high redshift.Comment: 19 pages, 12 figures, accepted to Ap
Lens Model and Time Delay Predictions for the Sextuply Lensed Quasar SDSS J2222+2745
SDSS J2222+2745 is a galaxy cluster at z=0.49, strongly lensing a quasar at
z=2.805 into six widely separated images. In recent HST imaging of the field,
we identify additional multiply lensed galaxies, and confirm the sixth quasar
image that was identified by Dahle et al. (2013). We used the Gemini North
telescope to measure a spectroscopic redshift of z=4.56 of one of the secondary
lensed galaxies. These data are used to refine the lens model of SDSS
J2222+2745, compute the time delay and magnifications of the lensed quasar
images, and reconstruct the source image of the quasar host and a second lensed
galaxy at z=2.3. This second galaxy also appears in absorption in our Gemini
spectra of the lensed quasar, at a projected distance of 34 kpc. Our model is
in agreement with the recent time delay measurements of Dahle et al. (2015),
who found tAB=47.7+/-6.0 days and tAC=-722+/-24 days. We use the observed time
delays to further constrain the model, and find that the model-predicted time
delays of the three faint images of the quasar are tAD=502+/-68 days,
tAE=611+/-75 days, and tAF=415+/-72 days. We have initiated a follow-up
campaign to measure these time delays with Gemini North. Finally, we present
initial results from an X-ray monitoring program with Swift, indicating the
presence of hard X-ray emission from the lensed quasar, as well as extended
X-ray emission from the cluster itself, which is consistent with the lensing
mass measurement and the cluster velocity dispersion.Comment: 16 pages, 11 figures; submitted to Ap
Star Formation at at z = 2.481 in the Lensed Galaxy SDSS J1110+6459. II. What is Missed at the Normal Resolution of the Hubble Space Telescope?
For lensed galaxy SGAS J111020.0+645950.8 at redshift z = 2.481, which is magnified by a factor of 28 ± 8, we analyze the morphology of star formation, as traced by rest-frame ultraviolet emission, in both the highly magnified source plane and simulations of how this galaxy would appear without lensing magnification. Were this galaxy not lensed, but rather drawn from a Hubble Space Telescope deep field, we would conclude that almost all its star formation arises from an exponential disk (Sérsic index of 1.0 ± 0.4) with an effective radius of r[subscript e]=2.7 ± 0.3 measured from two-dimensional fitting to F606W using Galfit, and r[subscript e]=1.9 ± 0.1 kpc measured by fitting a radial profile to F606W elliptical isophotes. At the normal spatial resolution of the deep fields, there is no sign of clumpy star formation within SGAS J111020.0+645950.8. However, the enhanced spatial resolution enabled by gravitational lensing tells a very different story; much of the star formation arises in two dozen clumps with sizes of r = 30–50 pc spread across the 7 kpc length of the galaxy. The color and spatial distribution of the diffuse component suggests that still-smaller clumps are unresolved. Despite this clumpy, messy morphology, the radial profile is still well-characterized by an exponential profile. In this lensed galaxy, stars are forming in complexes with sizes well below 100 pc; such sizes are wholly unexplored by surveys of galaxy evolution at 1 < z < 3
Strong Lens Models for 37 Clusters of Galaxies from the SDSS Giant Arcs Survey
We present strong gravitational lensing models for 37 galaxy clusters from
the SDSS Giant Arcs Survey. We combine data from multi-band Hubble Space
Telescope WFC3imaging, with ground-based imaging and spectroscopy from
Magellan, Gemini, APO, and MMT, in order to detect and spectroscopically
confirm new multiply-lensed background sources behind the clusters. We report
spectroscopic or photometric redshifts of sources in these fields, including
cluster galaxies and background sources. Based on all available lensing
evidence, we construct and present strong lensing mass models for these galaxy
clusters.Comment: 53 pages; submitted to ApJ
An experimental investigation of the relative strength of the silica polymorphs quartz, coesite and stishovite
In this study, quartz, coesite and stishovite were deformed concurrently with an olivine reference sample at high pressure and 850±50°C. Olivine deformed with an effective stress exponent (n) of 6.0_{+3.1}^{-2.2}, which we interpret to indicate that the Peierls creep deformation mechanism was active in the olivine. Quartz and coesite had very similar strengths and deformed by a mechanism with n = 2.8_{+1.2}^{-0.9} and 2.9_{+1.3}^{-0.9} respectively, which are consistent with previous measurements of power‐law creep in these phases. Stishovite deformed with n = 8.1_{+3.7}^{-2.7} and was stronger than both olivine and the other silica polymorphs. The high stress exponent of stishovite is greater than that typically observed for power‐law creep, indicating it is probably (but not certainly) deforming by Peierls creep. The rheology of SiO₂ minerals appears therefore to be strongly affected by the change in silicon‐coordination and density from 4‐fold in quartz and coesite to 6‐fold in stishovite. If the effect of Si‐coordination can be generalised, the increase in Si‐coordination (and density) associated with bridgmanite formation may explain the 10‐100 fold viscosity increase around 660km depth in the Earth
Star Formation at z = 2.481 in the Lensed Galaxy SDSS J1110+6459: Star Formation Down to 30 pc Scales
We present measurements of the surface density of star formation, the star-forming clump luminosity function, and the clump size distribution function, for the lensed galaxy SGAS J111020.0+645950.8 at a redshift of z =2.481. The physical size scales that we probe, radii r = 30-50 pc, are considerably smaller scales than have yet been studied at these redshifts. The star formation surface density we find within these small clumps is consistent with surface densities measured previously for other lensed galaxies at similar redshift. Twenty-two percent of the rest-frame ultraviolet light in this lensed galaxy arises from small clumps, with r is less than 100 pc. Within the range of overlap, the clump luminosity function measured for this lensed galaxy is remarkably similar to those of z is approximately 0 galaxies. In this galaxy, star-forming regions smaller than 100 pc-physical scales not usually resolved at these redshifts by current telescopes-are important locations of star formation in the distant universe. If this galaxy is representative, this may contradict the theoretical picture in which the critical size scale for star formation in the distant universe is of order 1 kiloparsec. Instead, our results suggest that current telescopes have not yet resolved the critical size scales of star-forming activity in galaxies over most of cosmic time
Lens Model and Source Reconstruction Reveal the Morphology and Star Formation Distribution in the Cool Spiral LIRG SGAS J143845.1145407
We present () imaging and grism spectroscopy
of a strongly lensed LIRG at , SGAS 143845.1145407, and use the
magnification boost of gravitational lensing to study the distribution of star
formation throughout this galaxy. Based on the imaging data, we create a
lens model for this system; we compute the mass distribution and magnification
map of the foreground lens. We find that the magnification of the
lensed galaxy ranges between and , with a total magnification (measured
over all the images of the source) of . We find that
the total projected mass density within kpc of the brightest cluster
galaxy is . Using the lens model we
create a source reconstruction for SGAS 143845.1145407, which paired with a
faint detection of H in the grism spectroscopy, allows us to finally
comment directly on the distribution of star formation in a LIRG. We
find widespread star formation across this galaxy, in agreement with the
current understanding of these objects. However, we note a deficit of H
emission in the nucleus of SGAS 143845.1145407, likely due to dust
extinction.Comment: 7 pages, 8 figures, 2 table
Longitudinal Association of Maternal Attempt to Lose Weight During the Postpartum Period and Child Obesity at Age 3 Years
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93678/1/oby.2011.25.pd
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