3,442 research outputs found
The SL2S Galaxy-scale Lens Sample. III. Lens Models, Surface Photometry and Stellar Masses for the final sample
We present Hubble Space Telescope (HST) imaging data and CFHT Near IR
ground-based images for the final sample of 56 candidate galaxy-scale lenses
uncovered in the CFHT Legacy Survey as part of the Strong Lensing in the Legacy
Survey (SL2S) project. The new images are used to perform lens modeling,
measure surface photometry, and estimate stellar masses of the deflector
early-type galaxies. Lens modeling is performed on the HST images (or CFHT when
HST is not available) by fitting the spatially extended light distribution of
the lensed features assuming a singular isothermal ellipsoid mass profile and
by reconstructing the intrinsic source light distribution on a pixelized grid.
Based on the analysis of systematic uncertainties and comparison with inference
based on different methods we estimate that our Einstein Radii are accurate to
\sim3%. HST imaging provides a much higher success rate in confirming
gravitational lenses and measuring their Einstein radii than CFHT imaging does.
Lens modeling with ground-based images however, when successful, yields
Einstein radius measurements that are competitive with spaced-based images.
Information from the lens models is used together with spectroscopic
information from the companion paper IV to classify the systems, resulting in a
final sample of 39 confirmed (grade-A) lenses and 17 promising candidates. The
redshifts of the main deflector span a range 0.3<zd< 0.8, providing an
excellent sample for the study of the cosmic evolution of the mass distribution
of early-type galaxies over the second half of the history of the Universe.Comment: Submitted to The Astrophysical Journa
Performance analysis of a parallel, multi-node pipeline for DNA sequencing
Post-sequencing DNA analysis typically consists of read mapping followed by variant calling and is very time-consuming, even on a multi-core machine. Recently, we proposed Halvade, a parallel, multi-node implementation of a DNA sequencing pipeline according to the GATK Best Practices recommendations. The MapReduce programming model is used to distribute the workload among different workers. In this paper, we study the impact of different hardware configurations on the performance of Halvade. Benchmarks indicate that especially the lack of good multithreading capabilities in the existing tools (BWA, SAMtools, Picard, GATK) cause suboptimal scaling behavior. We demonstrate that it is possible to circumvent this bottleneck by using multiprocessing on high-memory machines rather than using multithreading. Using a 15-node cluster with 360 CPU cores in total, this results in a runtime of 1 h 31 min. Compared to a single-threaded runtime of similar to 12 days, this corresponds to an overall parallel efficiency of 53%
The SL2S Galaxy-scale Lens Sample. IV. The dependence of the total mass density profile of early-type galaxies on redshift, stellar mass, and size
We present optical and near infrared spectroscopy obtained at Keck, VLT, and
Gemini for a sample of 36 secure strong gravitational lens systems and 17
candidates identified as part of the SL2S survey. The deflectors are massive
early-type galaxies in the redshift range z_d=0.2-0.8, while the lensed sources
are at z_s=1-3.5. We combine this data with photometric and lensing
measurements presented in the companion paper III and with lenses from the
SLACS and LSD surveys to investigate the cosmic evolution of the internal
structure of massive early-type galaxies over half the age of the universe. We
study the dependence of the slope of the total mass density profile \gamma'
(\rho(r)\propto r^{-\gamma'}) on stellar mass, size, and redshift. We find that
two parameters are sufficent to determine \gamma' with less than 6% residual
scatter. At fixed redshift, \gamma' depends solely on the surface stellar mass
density \partial \gamma'/ \partial \Sigma_*=0.38\pm 0.07, i.e. galaxies with
denser stars also have steeper slopes. At fixed M_* and R_{eff}, \gamma'
depends on redshift, in the sense that galaxies at a lower redshift have
steeper slopes (\partial \gamma' / \partial z = -0.31\pm 0.10). However, the
mean redshift evolution of \gamma' for an individual galaxy is consistent with
zero d\gamma'/dz=-0.10\pm0.12. This result is obtained by combining our
measured dependencies of \gamma' on z,M_*,R_{eff} with the evolution of the
R_{eff}-M_* taken from the literature, and is broadly consistent with current
models of the formation and evolution of massive early-type galaxies. Detailed
quantitative comparisons of our results with theory will provide qualitatively
new information on the detailed physical processes at work.Comment: Submitted to The Astrophysical Journa
The SL2S Galaxy-scale Lens Sample. V. Dark Matter Halos and Stellar IMF of Massive Early-type Galaxies out to Redshift 0.8
We investigate the cosmic evolution of the internal structure of massive
early-type galaxies over half of the age of the Universe. We perform a joint
lensing and stellar dynamics analysis of a sample of 81 strong lenses from the
SL2S and SLACS surveys and combine the results with a hierarchical Bayesian
inference method to measure the distribution of dark matter mass and stellar
IMF across the population of massive early-type galaxies. Lensing selection
effects are taken into account. We find that the dark matter mass projected
within the inner 5 kpc increases for increasing redshift, decreases for
increasing stellar mass density, but is roughly constant along the evolutionary
tracks of early-type galaxies. The average dark matter slope is consistent with
that of an NFW profile, but is not well constrained. The stellar IMF
normalization is close to a Salpeter IMF at and scales
strongly with increasing stellar mass. No dependence of the IMF on redshift or
stellar mass density is detected. The anti-correlation between dark matter mass
and stellar mass density supports the idea of mergers being more frequent in
more massive dark matter halos.Comment: Accepted for publication on The Astrophysical Journal. Revised
version. (25 pages, 18 figures
Star formation in W3 - AFGL333: Young stellar content, properties and roles of external feedback
One of the key questions in the field of star formation is the role of
stellar feedback on subsequent star formation process. The W3 giant molecular
cloud complex at the western border of the W4 super bubble is thought to be
influenced by the stellar winds of the massive stars in W4. AFGL333 is a ~10^4
Msun cloud within W3. This paper presents a study of the star formation
activity within AFGL333 using deep JHKs photometry obtained from the NOAO
Extremely Wide-Field Infrared Imager combined with Spitzer-IRAC-MIPS
photometry. Based on the infrared excess, we identify 812 candidate young
stellar objects in the complex, of which 99 are classified as Class I and 713
are classified as Class II sources. The stellar density analysis of young
stellar objects reveals three major stellar aggregates within AFGL333, named
here AFGL333-main, AFGL333-NW1 and AFGL333-NW2. The disk fraction within
AFGL333 is estimated to be ~50-60%. We use the extinction map made from the
H-Ks colors of the background stars to understand the cloud structure and to
estimate the cloud mass. The CO-derived extinction map corroborates the cloud
structure and mass estimates from NIR color method. From the stellar mass and
cloud mass associated with AFGL333, we infer that the region is currently
forming stars with an efficiency of ~4.5% and at a rate of ~2 - 3 Msun
Myr-1pc-2. In general, the star formation activity within AFGL333 is comparable
to that of nearby low mass star-forming regions. We do not find any strong
evidence to suggest that the stellar feedback from the massive stars of nearby
W4 super bubble has affected the global star formation properties of the
AFGL333 region.Comment: 17 pages, 9 figures, Accepted for publication in Ap
A Four-Stage Method for Developing Early Interventions for Alcohol Among Aboriginal Adolescents
This paper details a four-stage methodology for developing early alcohol interventions for at-risk Aboriginal youth. Stage 1 was an integrative approach to Aboriginal education that upholds Aboriginal traditional wisdom supporting respectful relationships to the Creator, to the land and to each other. Stage 2 used quantitative methods to investigate associations between personality risk factors and risky drinking motives. Stage 3 used qualitative interviews to further understand the contexts and circumstances surrounding drinking behaviour within a larger cultural context. Stage 3 involved tailoring personality- matched, motive-specific brief interventions to meet at-risk adolescents’ needs. Stage 4 involved an efficacy test of the interventions. This novel methodology has significance for future program development to meet diverse social, cultural and health needs of at-risk adolescents
Hopelessness and Excessive Drinking among Aboriginal Adolescents: The Mediating Roles of Depressive Symptoms and Drinking to Cope
Canadian Aboriginal youth show high rates of excessive drinking, hopelessness, and depressive symptoms. We propose that Aboriginal adolescents with higher levels of hopelessness are more susceptible to depressive symptoms, which in turn predispose them to drinking to cope—which ultimately puts them at risk for excessive drinking. Adolescent drinkers (n = 551; 52% boys; mean age = 15.9 years) from 10 Canadian schools completed a survey consisting of the substance use risk profile scale (hopelessness), the brief symptom inventory (depressive symptoms), the drinking motives questionnaire—revised (drinking to cope), and quantity, frequency, and binge measures of excessive drinking. Structural equation modeling demonstrated the excellent fit of a model linking hopelessness to excessive drinking indirectly via depressive symptoms and drinking to cope. Bootstrapping indicated that this indirect effect was significant. Both depressive symptoms and drinking to cope should be intervention targets to prevent/decrease excessive drinking among Aboriginal youth high in hopelessness
V1647 Ori (IRAS 05436-0007) in Outburst: the First Three Months
We report on photometric (BVRIJHK) and low dispersion spectroscopic
observations of V1647 Ori, the star that drives McNeil's Nebula, between 10
February and 7 May 2004. The star is photometrically variable atop a general
decline in brightness of about 0.3-0.4 magnitudes during these 87 days. The
spectra are featureless, aside from H-alpha and the Ca II infrared triplet in
emission, and a Na I D absorption feature. The Ca II triplet line ratios are
typical of young stellar objects. The H-alpha equivalent width may be modulated
on a period of about 60 days. The post-outburst extinction appears to be less
than 7 mag. The data are suggestive of an FU Orionis-like event, but further
monitoring will be needed to definitively characterize the outburst.Comment: Accepted for publication in the Astronomical Journa
Depression, anxiety, and stress among hangover-sensitive and hangover-resistant drinkers
This study investigated potential differences in baseline (i.e., non-hangover-related) levels of depression, anxiety, and stress between individuals who are sensitive to and those resistant to hangovers after consuming alcohol. Participants included 5111 university students from the Netherlands and the U.K., including 3205 hangover-sensitive and 1906 hangover-resistant drinkers. All participants completed surveys on their demographics, alcohol consumption, and hangover susceptibility (whether they experienced a hangover in the past 12 months), as well as their baseline levels of depression, anxiety, and stress on the DASS-21 scale. The results showed that hangover-sensitive drinkers had significantly higher levels of anxiety and stress, but not depression, compared to hangover-resistant drinkers. However, the observed differences between the two groups were small, with a magnitude of less than 1 out of 42 points on the DASS-21 anxiety and stress subscales, and are thus unlikely to be clinically meaningful
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