170 research outputs found
Prospects for CDM sub-halo detection using high angular resolution observations
In the CDM scenario, dark matter halos are assembled hierarchically from
smaller subunits. A long-standing problem with this picture is that the number
of sub-halos predicted by CDM simulations is orders of magnitudes higher than
the known number of satellite galaxies in the vicinity of the Milky Way. A
plausible way out of this problem could be that the majority of these sub-halos
somehow have so far evaded detection. If such "dark galaxies" do indeed exist,
gravitational lensing may offer one of the most promising ways to detect them.
Dark matter sub-halos in the 1e6 - 1e10 solar mass range should cause strong
gravitational lensing on (sub)milliarcsecond scales. We study the feasibility
of a strong lensing detection of dark sub-halos by deriving the image
separations expected for density profiles favoured by recent simulations and
comparing these to the angular resolution of both existing and upcoming
observational facilities. We find that there is a reasonable probability to
detect sub-halo lensing effects in high resolution observations at radio
wavelengths, such as produced by the upcoming VSOP-2 satellite, and thereby
test the existence of dark galaxies.Comment: 9 pages, 5 figures, Proceedings for "The Universe under the
Microscope" (AHAR 2008), held in Bad Honnef (Germany) in April 2008, to be
published in Journal of Physics: Conference Series by Institute of Physics
Publishing, R. Schoedel, A. Eckart, S. Pfalzner, and E. Ros (eds.
Strong lensing by subhalos in the dwarf-galaxy mass range I: Image separations
The cold dark matter scenario predicts that a large number of dark subhalos
should be located within the halo of each Milky-way sized galaxy. One tell-tale
signature of such dark subhalos could be additional milliarcsecond-scale image
splitting of quasars previously known to be multiply-imaged on arcsecond
scales. Here, we estimate the image separations for the subhalo density
profiles favoured by recent N-body simulations, and compare these to the
angular resolution of both existing and upcoming observational facilities. We
find, that the image separations produced are very sensitive to the exact
subhalo density profile assumed, but in all cases considerably smaller than
previous estimates based on the premise that subhalos can be approximated by
singular isothermal spheres. Only the most optimistic subhalo models produce
image separations that would be detectable with current technology, and many
models produce image separations that will remain unresolved with all
telescopes expected to become available in the foreseeable future. Detections
of dark subhalos through image-splitting effects will therefore be far more
challenging than currently believed, albeit not necessarily impossible.Comment: 7 pages, 3 figures, accepted for publication in Ap
Near-IR search for lensed supernovae behind galaxy clusters: III. Implications for cluster modeling and cosmology
Massive galaxy clusters at intermediate redshifts act as gravitational lenses
that can magnify supernovae (SNe) occurring in background galaxies. We assess
the possibility to use lensed SNe to put constraints on the mass models of
galaxy clusters and the Hubble parameter at high redshift. Due to the standard
candle nature of Type Ia supernovae (SNe Ia), observational information on the
lensing magnification from an intervening galaxy cluster can be used to
constrain the model for the cluster mass distribution. A statistical analysis
using parametric cluster models was performed to investigate the possible
improvements from lensed SNe Ia for the accurately modeled galaxy cluster A1689
and the less well constrained cluster A2204. Time delay measurements obtained
from SNe lensed by accurately modeled galaxy clusters can be used to measure
the Hubble parameter. For a survey of A1689 we estimate the expected rate of
detectable SNe Ia and of multiply imaged SNe. The velocity dispersion and core
radius of the main cluster potential show strong correlations with the
predicted magnifications and can therefore be constrained by observations of
SNe Ia in background galaxies. This technique proves especially powerful for
galaxy clusters with only few known multiple image systems. The main
uncertainty for measurements of the Hubble parameter from the time delay of
strongly lensed SNe is due to cluster model uncertainties. For the extremely
well modeled cluster A1689, a single time delay measurement could be used to
determine the Hubble parameter with a precision of ~ 10%. We conclude that
observations of SNe Ia behind galaxy clusters can be used to improve the mass
modeling of the large scale component of galaxy clusters and thus the
distribution of dark matter. Time delays from SNe strongly lensed by accurately
modeled galaxy clusters can be used to measure the Hubble constant at high
redshifts.Comment: 10 pages, 8 figures, 3 tables. Accepted for publication in A&
Detection of minimal residual disease identifies differences in treatment response between T-ALL and precursor B-ALL
We performed sensitive polymerase chain reaction-based minimal residual
disease (MRD) analyses on bone marrow samples at 9 follow-up time points
in 71 children with T-lineage acute lymphoblastic leukemia (T-ALL) and
compared the results with the precursor B-lineage ALL (B-ALL) results (n =
210) of our previous study. At the first 5 follow-up time points, the
frequency of MRD-positive patients and the MRD levels were higher in T-ALL
than in precursor-B-ALL, reflecting the more frequent occurrence of
resistant disease in T-ALL. Subsequently, patients were classified
according to their MRD level at time point 1 (TP1), taken at the end of
induction treatment (5 weeks), and at TP2 just before the start of
consolidation treatment (3 months). Patients were considered at low risk
if TP1 and TP2 were MRD negative and at high risk if MRD levels at TP1 and
TP2 were 10(-3) or higher; remaining patients were considered at
intermediate risk. The relative distribution of patients with T-ALL (n =
43) over the MRD-based risk groups differed significantly from that of
precursor B-ALL (n = 109). Twenty-three percent of patients with T-ALL and
46% of patients with precursor B-ALL were classified in the low-risk group
(P =.01) and had a 5-year relapse-free survival (RFS) rate of 98% or
greater. In contrast, 28% of patients with T-ALL were classified in the
MRD-based high-risk group compared to only 11% of patients with precursor
B-ALL (P =.02), and the RFS rates were 0% and 25%, respectively (P =.03).
Not only was the distribution of patients with T-ALL different over the
MRD-based risk groups, the prognostic value of MRD levels at TP1 and TP2
was higher in T-ALL (larger RFS gradient), and consistently higher RFS
rates were found for MRD-negative T-ALL patients at the first 5 follow-up
time points
Near-IR Search for Lensed Supernovae Behind Galaxy Clusters - II. First Detection and Future Prospects
Powerful gravitational telescopes in the form of massive galaxy clusters can
be used to enhance the light collecting power over a limited field of view by
about an order of magnitude in flux. This effect is exploited here to increase
the depth of a survey for lensed supernovae at near-IR wavelengths. A pilot SN
search program conducted with the ISAAC camera at VLT is presented. Lensed
galaxies behind the massive clusters A1689, A1835 and AC114 were observed for a
total of 20 hours split into 2, 3 and 4 epochs respectively, separated by
approximately one month to a limiting magnitude J<24 (Vega). Image subtractions
including another 20 hours worth of archival ISAAC/VLT data were used to search
for transients with lightcurve properties consistent with redshifted
supernovae, both in the new and reference data. The feasibility of finding
lensed supernovae in our survey was investigated using synthetic lightcurves of
supernovae and several models of the volumetric Type Ia and core-collapse
supernova rates as a function of redshift. We also estimate the number of
supernova discoveries expected from the inferred star formation rate in the
observed galaxies. The methods consistently predict a Poisson mean value for
the expected number of SNe in the survey between N_SN=0.8 and 1.6 for all
supernova types, evenly distributed between core collapse and Type Ia SN. One
transient object was found behind A1689, 0.5" from a galaxy with photometric
redshift z_gal=0.6 +- 0.15. The lightcurve and colors of the transient are
consistent with being a reddened Type IIP SN at z_SN=0.59. The lensing model
predicts 1.4 magnitudes of magnification at the location of the transient,
without which this object would not have been detected in the near-IR ground
based search described in this paper (unlensed magnitude J~25). (abridged)Comment: Accepted by AA, matches journal versio
Near-IR search for lensed supernovae behind galaxy clusters: I. Observations and transient detection efficiency
Massive galaxy clusters at intermediate redshift can magnify the flux of
distant background sources by several magnitudes and we exploit this effect to
search for lensed distant supernovae that may otherwise be too faint to be
detected. A supernova search was conducted at near infrared wavelengths using
the ISAAC instrument at the VLT. The galaxy clusters Abell 1689, Abell 1835 and
AC114 were observed at multiple epochs of 2 hours of exposure time, separated
by a month. Image-subtraction techniques were used to search for transient
objects with light curve properties consistent with supernovae, both in our new
and archival ISAAC/VLT data. The limiting magnitude of the individual epochs
was estimated by adding artificial stars to the subtracted images. Most of the
epochs reach 90% detection efficiency at SZ(J) ~= 23.8-24.0 mag (Vega). Two
transient objects, both in archival images of Abell 1689 and AC114, were
detected. The transient in AC114 coincides - within the position uncertainty -
with an X-ray source and is likely to be a variable AGN at the cluster
redshift. The transient in Abell 1689 was found at SZ=23.24 mag, ~0.5 arcsec
away from a galaxy with photometric redshift z=0.6 +/-0.15. The light curves
and the colors of the transient are consistent with a reddened Type IIP
supernova at redshift z=0.59 +/- 0.05. The lensing model of Abell 1689 predicts
~1.4 mag of magnification at the position of the transient, making it the most
magnified supernova ever found and only the second supernova found behind a
galaxy cluster. Our pilot survey has demonstrated the feasibility to find
distant gravitationally magnified supernovae behind massive galaxy clusters.
One likely supernova was found behind Abell 1689, in accordance with the
expectations for this survey, as shown in an accompanying analysis paper.Comment: Language-edited version, 9 pages, 6 figures, accepted by A&
A highly magnified supernova at z=1.703 behind the massive galaxy cluster Abell 1689
Our ability to study the most remote supernova explosions, crucial for the
understanding of the evolution of the high-redshift universe and its expansion
rate, is limited by the light collection capabilities of telescopes. However,
nature offers unique opportunities to look beyond the range within reach of our
unaided instruments thanks to the light-focusing power of massive galaxy
clusters. Here we report on the discovery of one of the most distant supernovae
ever found, at redshift, z=1.703. Due to a lensing magnification factor of
4.3\pm0.3, we are able to measure a lightcurve of the supernova, as well as
spectroscopic features of the host galaxy with a precision comparable to what
will otherwise only be possible with future generation telescopes.Comment: 19 pages, 4 figures, 1 table, accepted to ApJ
Comparison of major depression diagnostic classification probability using the SCID, CIDI, and MINI diagnostic interviews among women in pregnancy or postpartum: An individual participant data meta-analysis
Objectives A previous individual participant data meta-analysis (IPDMA) identified differences in major depression classification rates between different diagnostic interviews, controlling for depressive symptoms on the basis of the Patient Health Questionnaire-9. We aimed to determine whether similar results would be seen in a different population, using studies that administered the Edinburgh Postnatal Depression Scale (EPDS) in pregnancy or postpartum. Methods Data accrued for an EPDS diagnostic accuracy IPDMA were analysed. Binomial generalised linear mixed models were fit to compare depression classification odds for the Mini International Neuropsychiatric Interview (MINI), Composite International Diagnostic Interview (CIDI), and Structured Clinical Interview for DSM (SCID), controlling for EPDS scores and participant characteristics. Results Among fully structured interviews, the MINI (15 studies, 2,532 participants, 342 major depression cases) classified depression more often than the CIDI (3 studies, 2,948 participants, 194 major depression cases; adjusted odds ratio [aOR] = 3.72, 95% confidence interval [CI] [1.21, 11.43]). Compared with the semistructured SCID (28 studies, 7,403 participants, 1,027 major depression cases), odds with the CIDI (interaction aOR = 0.88, 95% CI [0.85, 0.92]) and MINI (interaction aOR = 0.95, 95% CI [0.92, 0.99]) increased less as EPDS scores increased. Conclusion Different interviews may not classify major depression equivalently
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