157 research outputs found
Understanding Trans-Sequential Ethnography and its Place in the Contemporary Sociological Landscape
What is trans-sequential ethnography? What defines it â both as a theoretical apparatus and a way of practicing ethnography? We address these questions by situating trans-sequential ethnography, also frequently known as trans-sequential analysis or TSA, within broader trends within the discipline of sociology as a whole. In particular, we argue that TSA can perhaps best be understood in two ways. First, we argue that it should be seen as standing within a long line of social theory which argues that the fundamental ontological condition of social life is one of, what we term, excess. Second, we argue that TSA should also be seen as a rather systematic attempt to overcome the methodological difficulties that sociologists (and ethnographers in particular) have encountered as a result of this ontological fact
Gravitational lensing reveals ionizing ultraviolet photons escaping from a distant galaxy
During the epoch of reionisation, neutral gas in the early Universe was
ionized by hard ultraviolet radiation emitted by young stars in the first
galaxies. To do so, ionizing ultraviolet photons must escape from the host
galaxy. We present Hubble Space Telescope observations of the gravitationally
lensed galaxy PSZ1-ARC G311.6602-18.4624, revealing bright, multiply-imaged
ionizing photon escape from a compact star-forming region through a narrow
channel in an optically thick gas. The gravitational lensing magnification
shows how ionizing photons escape this galaxy, contributing to the
re-ionization of the Universe. The multiple sight lines to the source probe
absorption by intergalactic neutral hydrogen on scales of no more than a few
hundred, perhaps even less than ten, parsec.Comment: 17 pages, 9 figures. Published in Scienc
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
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
Spatially Resolved Patchy Lyman- Emission Within the Central Kiloparsec of a Strongly Lensed Quasar Host Galaxy at z = 2.8
We report the detection of extended Lyman- emission from the host
galaxy of SDSS~J2222+2745, a strongly lensed quasar at . Spectroscopic
follow-up clearly reveals extended Lyman- in emission between two
images of the central active galactic nucleus (AGN). We reconstruct the lensed
quasar host galaxy in the source plane by applying a strong lens model to HST
imaging, and resolve spatial scales as small as 200 parsecs. In the
source plane we recover the host galaxy morphology to within a few hundred
parsecs of the central AGN, and map the extended Lyman- emission to its
physical origin on one side of the host galaxy at radii 0.5-2 kpc from
the central AGN. There are clear morphological differences between the
Lyman- and rest-frame ultraviolet stellar continuum emission from the
quasar host galaxy. Furthermore, the relative velocity profiles of quasar
Lyman-, host galaxy Lyman-, and metal lines in outflowing gas
reveal differences in the absorbing material affecting the AGN and host galaxy.
These data indicate the presence of patchy local intervening gas in front of
the central quasar and its host galaxy. This interpretation is consistent with
the central luminous quasar being obscured across a substantial fraction of its
surrounding solid angle, resulting in strong anisotropy in the exposure of the
host galaxy to ionizing radiation from the AGN. This work demonstrates the
power of strong lensing-assisted studies to probe spatial scales that are
currently inaccessible by other means.Comment: Accepted to ApJ Letters; 7 pages, 5 figure
Strong Lensing Model of SPT-CLJ0356-5337, a Major Merger Candidate at Redshift 1.0359
We present an analysis of the mass distribution inferred from strong lensing
by SPT-CL J0356-5337, a cluster of galaxies at redshift z = 1.0359 revealed in
the follow-up of the SPT-SZ clusters. The cluster has an Einstein radius of
Erad=14 for a source at z = 3 and a mass within 500 kpc of M_500kpc =
4.0+-0.8x10^14Msol. Our spectroscopic identification of three multiply-imaged
systems (z = 2.363, z = 2.364, and z = 3.048), combined with HST F606W-band
imaging allows us to build a strong lensing model for this cluster with an rms
of <0.3'' between the predicted and measured positions of the multiple images.
Our modeling reveals a two-component mass distribution in the cluster. One mass
component is dominated by the brightest cluster galaxy and the other component,
separated by ~170 kpc, contains a group of eight red elliptical galaxies
confined in a ~9'' (~70 kpc) diameter circle. We estimate the mass ratio
between the two components to be between 1:1.25 and 1:1.58. In addition,
spectroscopic data reveal that these two near-equal mass cores have only a
small velocity difference of 300 km/s between the two components. This small
radial velocity difference suggests that most of the relative velocity takes
place in the plane of the sky, and implies that SPT-CL J0356-5337 is a major
merger with a small impact parameter seen face-on. We also assess the relative
contributions of galaxy-scale halos to the overall mass of the core of the
cluster and find that within 800 kpc from the brightest cluster galaxy about
27% of the total mass can be attributed to visible and dark matter associated
with galaxies, whereas only 73% of the total mass in the core comes from
cluster-scale dark matter halos.Comment: 19 pages, 11 figures. Submitted to Ap
Impact on Diet Quality and Resilience in Urban Community Dwelling Obese Women with a Nutrition and Physical Activity Intervention
Objective: To examine the effect of a Tai Chi, resistance training, and behaviorally-based diet education intervention on dietary quality as well as resilience and physical resilience in obese older women. Design: Community health outreach with a quasi-experimental design. Setting: An urban senior center in Rhode Island. Participants: Thirty-three women, 85% were minorities, with mean age of 65±8.2 years and BMI of 37.3±4.6 kg/m2, were enrolled in the study at baseline however only 17 women in the intervention (EXD) group and 9 women in the wait-list control (CON) group completed the study. Measurement: Dietary quality and nutrition risk were measured using the Dietary Screening Tool (DST), resilience was measured by the Resilience Scale, and physical resilience was examined using the Physical Resilience Scale. Intervention: Participants in the EXD group engaged in 12 weeks of Tai Chi, resistance training, and behaviorally-based diet education. The diet education was based off of the modified Dietary Approaches to Stop Hypertension (DASH) diet and led by a Registered Dietitian. Results: There was no change in dietary quality by group or time. However the EXD group had significantly higher dietary quality compared to the control group (p=0.025) at post intervention, although there was no difference in nutrition risk category. There was no change seen in overall resilience, however the EXD group improved physical resilience (p=0.048). Conclusion: A community health outreach that involved Tai Chi, resistance training, and behaviorally-based diet education may promote higher dietary quality as well as improve physical resilience in obese older women
Hubble Constant Measurement from Three Large-separation Quasars Strongly Lensed by Galaxy Clusters
Tension between cosmic microwave backgroundâbased and distance ladderâbased determinations of the Hubble constant H 0 motivates the pursuit of independent methods that are not subject to the same systematic effects. A promising alternative, proposed by Refsdal in 1964, relies on the inverse scaling of H 0 with the delay between the arrival times of at least two images of a strongly lensed variable source such as a quasar. To date, Refsdalâs method has mostly been applied to quasars lensed by individual galaxies rather than by galaxy clusters. Using the three quasars strongly lensed by galaxy clusters (SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745) that have both multiband Hubble Space Telescope data and published time delay measurements, we derive H 0, accounting for the systematic and statistical sources of uncertainty. While a single time delay measurement does not yield a well-constrained H 0 value, analyzing the systems together tightens the constraint. Combining the six time delays measured in the three cluster-lensed quasars gives H 0 = 74.1 ± 8.0 km sâ1 Mpcâ1. To reach 1% uncertainty in H 0, we estimate that a sample size of order of 620 time delay measurements of similar quality as those from SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745 would be needed. Improving the lens modeling uncertainties by a factor of two and a half may reduce the needed sample size to 100 time delays, potentially reachable in the next decade
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