1,559 research outputs found
Hubble Frontier Field Free-Form Mass Mapping of the Massive Multiple-Merging Cluster MACSJ0717.5+3745
We examine the latest data on the cluster MACSJ0717.5+3745 from the Hubble
Frontier Fields campaign. The critically lensed area is the largest known of
any lens and very irregular making it a challenge for parametric modelling.
Using our Free-Form method we obtain an accurate solution, identify here many
new sets of multiple images, doubling the number of constraints and improving
the reconstruction of the dark matter distribution. Our reconstructed mass map
shows several distinct central substructures with shallow density profiles,
clarifying earlier work and defining well the relation between the dark matter
distribution and the luminous and X-ray peaks within the critically lensed
region. Using our free-form method, we are able to meaningfully subtract the
mass contribution from cluster members to the deflection field to trace the
smoothly distributed cluster dark matter distribution. We find 4 distinct
concentrations, 3 of which are coincident with the luminous matter. The fourth
peak has a significant offset from both the closest luminous and X-ray peaks.
These findings, together with dynamical data from the motions of galaxies and
gas will be important for uncovering the potentially important implications of
this extremely massive and intriguing system.Comment: 16 pages, 10 figures, 2 tables. Matches the verson submitted to
mnras. New table (A2) included with additional system candidate
A Rigorous Free-form Lens Model of Abell 2744 to Meet the Hubble Frontier Fields Challenge
Hubble Frontier Fields (HFF) imaging of the most powerful lensing clusters
provides access to the most magnified distant galaxies. The challenge is to
construct lens models capable of describing these complex massive, merging
clusters so that individual lensed systems can be reliably identified and their
intrinsic properties accurately derived. We apply the free-form lensing method
(WSLAP+) to A2744, providing a model independent map of the cluster mass,
magnification, and geometric distance estimates to multiply-lensed sources. We
solve simultaneously for a smooth cluster component on a pixel grid, together
with local deflections by the cluster member galaxies. Combining model
prediction with photometric redshift measurements, we correct and complete
several systems recently claimed, and identify 4 new systems - totalling 65
images of 21 systems spanning a redshift range of 1.4<z<9.8. The reconstructed
mass shows small enhancements in the directions where significant amounts of
hot plasma can be seen in X-ray. We compare photometric redshifts with
"geometric redshifts", finding a high level of self-consistency. We find
excellent agreement between predicted and observed fluxes - with a best-fit
slope of 0.999+-0.013 and an RMS of ~0.25 mag, demonstrating that our
magnification correction of the lensed background galaxies is very reliable.
Intriguingly, few multiply-lensed galaxies are detected beyond z~7.0, despite
the high magnification and the limiting redshift of z~11.5 permitted by the HFF
filters. With the additional HFF clusters we can better examine the
plausibility of any pronounced high-z deficit, with potentially important
implications for the reionization epoch and the nature of dark matter.Comment: Accepted for publication in ApJ with newly identified lensed images
in complete HFF dat
Probing the mass loss history of the yellow hypergiant IRC+10420
We have used the sub-millimeter array to image the molecular envelope around
IRC+10420. Our observations reveal a large and clumpy expanding envelope around
the star. The molecular envelope shows a clear asymmetry in CO J=2--1
emission in the South-West direction. The elongation of the envelope is found
even more pronounced in the emission of CO J=2--1 and SO J=6--5. A small positional velocity gradient across velocity channels
is seen in these lines, suggesting the presence of a weak bipolar outflow in
the envelope of IRC+10420. In the higher resolution CO J=2--1 map, we
find that the envelope has two components: (1) an inner shell (shell I) located
between radius of about 1"-2"; (2) an outer shell (shell II) located between 3"
to 6" in radius. These shells represent two previous mass-loss episodes from
IRC+10420. We attempt to derive in self-consistent manner the physical
conditions inside the envelope by modelling the dust properties, and the
heating and cooling of molecular gas. We estimate a mass loss rate of 9
10 M yr for shell I and 7 10 M yr
for shell II. The gas temperature is found to be unusually high in IRC+10420 in
comparison with other oxygen-rich envelopes. The elevated gas temperature is
mainly due to higher heating rate, which results from the large luminosity of
the central s tar. We also derive an isotopic ratio C/C = 6.Comment: 30 pages, 14 figures. Accepted for publication in The Astrophysical
Journa
A Free-Form Prediction for the Reappearance of Supernova Refsdal in the Hubble Frontier Fields Cluster MACSJ1149.5+2223
The massive cluster MACSJ1149.5+2223(z=0.544) displays five very large lensed
images of a well resolved spiral galaxy at . It is within
one of these images that the first example of a multiply-lensed supernova has
been detected recently as part of the Grism Lens-Amplified Survey from Space.
The depth of this data also reveals many HII regions within the lensed spiral
galaxy which we identify between the five counter-images. Here we expand the
capability of our free-form method to incorporate these HII regions locally,
with other reliable lensed galaxies added for a global solution. This improved
accuracy allows us to estimate when the Refsdal supernova will appear within
the other lensed images of the spiral galaxy to an accuracy of 7\%. We
predict this supernova will reappear in one of the counter-images
(RA=11:49:36.025, DEC=+22:23:48.11, J2000) and on November 1 2015 (with
an estimated error of 25 days) it will be at the same phase as it was
when it was originally discovered, offering a unique opportunity to study the
early phases of this supernova and to examine the consistency of the mass model
and the cosmological model that have an impact on the time delay prediction.Comment: 12 images, 11 pages. Mateches accepted version in MNRAS. MNRAS in
pres
Categorization of species as native or nonnative using DNA sequence signatures without a complete reference library.
New genetic diagnostic approaches have greatly aided efforts to document global biodiversity and improve biosecurity. This is especially true for organismal groups in which species diversity has been underestimated historically due to difficulties associated with sampling, the lack of clear morphological characteristics, and/or limited availability of taxonomic expertise. Among these methods, DNA sequence barcoding (also known as "DNA barcoding") and by extension, meta-barcoding for biological communities, has emerged as one of the most frequently utilized methods for DNA-based species identifications. Unfortunately, the use of DNA barcoding is limited by the availability of complete reference libraries (i.e., a collection of DNA sequences from morphologically identified species), and by the fact that the vast majority of species do not have sequences present in reference databases. Such conditions are critical especially in tropical locations that are simultaneously biodiversity rich and suffer from a lack of exploration and DNA characterization by trained taxonomic specialists. To facilitate efforts to document biodiversity in regions lacking complete reference libraries, we developed a novel statistical approach that categorizes unidentified species as being either likely native or likely nonnative based solely on measures of nucleotide diversity. We demonstrate the utility of this approach by categorizing a large sample of specimens of terrestrial insects and spiders (collected as part of the Moorea BioCode project) using a generalized linear mixed model (GLMM). Using a training data set of known endemic (n = 45) and known introduced species (n = 102), we then estimated the likely native/nonnative status for 4,663 specimens representing an estimated 1,288 species (412 identified species), including both those specimens that were either unidentified or whose endemic/introduced status was uncertain. Using this approach, we were able to increase the number of categorized specimens by a factor of 4.4 (from 794 to 3,497), and the number of categorized species by a factor of 4.8 from (147 to 707) at a rate much greater than chance (77.6% accuracy). The study identifies phylogenetic signatures of both native and nonnative species and suggests several practical applications for this approach including monitoring biodiversity and facilitating biosecurity
Bad News Travels Slowly: Size, Analyst Coverage and the Profitability of Momentum Strategies
A number of theories have been proposed to explain the medium-term momentum in stock returns identified by Jegadeesh and Titman (1993). We test one such theory--based on the gradual-information-diffusion model of Hong and Stein (1997)--and establish three key results. First, once one moves past the very smallest stocks (where thin market-making capacity appears to be an issue) the profitability of momentum strategies declines sharply with firm size. Second, holding size fixed, momentum strategies work particularly well among stocks which have low analyst coverage. Finally, there is a strong asymmetry: the effect of analyst coverage is much more pronounced for stocks that are past losers than for stocks that are past winners. These findings are consistent with the hypothesis that firm-specific information only gradually across the investing public.
Geometric Corroboration of the Earliest Lensed Galaxy at z ≃ 10.8 from Robust Free-form Modelling
A multiply lensed galaxy, MACS0647-JD, with a probable photometric redshift of z ≃ 10.7_(-0.4)^(+0.6) is claimed to constitute one of the very earliest known galaxies, formed well before reionization was completed. However, spectral evidence that MACS0647-JD lies at high redshift has proven infeasible and so here we seek an independent-lensing-based "geometric redshift" derived from the angles between the three lensed images of MACS0647-JD, using our free-form mass model (WSLAP+) for the lensing cluster MACSJ0647.7+7015 (at z = 0.591). Our lens model uses the nine sets of multiple images, including those of MACS0647-JD, identified by the CLASH survey toward this cluster. We convincingly exclude the low-redshift regime of z < 3, for which convoluted critical curves are generated by our method, as the solution bends to accommodate the wide angles of MACS0647-JD for this low redshift. Instead, a best fit to all sets of lensed galaxy positions and redshifts provides a geometric redshift of z≃ 10.8_(-0.4)^(+0.3) for MACS0647-JD, strongly supporting the higher photometric redshift solution. Importantly, we find a tight linear relation between the relative brightnesses of all nine sets of multiply lensed images and their relative magnifications as predicted by our model. This agreement provides a benchmark for the quality of the lens model, and establishes the robustness of our free-form lensing method for measuring model-independent geometric source distances and for deriving objective central cluster mass distributions. After correcting for its magnification the luminosity of MACS0647-JD remains relatively high at M UV = −19.4, which is within a factor of a few in flux of some surprisingly luminous z sime 10–11 candidates discovered recently in Hubble blank field surveys
Geometric Corroboration of the Earliest Lensed Galaxy at z ≃ 10.8 from Robust Free-form Modelling
A multiply lensed galaxy, MACS0647-JD, with a probable photometric redshift of z ≃ 10.7_(-0.4)^(+0.6) is claimed to constitute one of the very earliest known galaxies, formed well before reionization was completed. However, spectral evidence that MACS0647-JD lies at high redshift has proven infeasible and so here we seek an independent-lensing-based "geometric redshift" derived from the angles between the three lensed images of MACS0647-JD, using our free-form mass model (WSLAP+) for the lensing cluster MACSJ0647.7+7015 (at z = 0.591). Our lens model uses the nine sets of multiple images, including those of MACS0647-JD, identified by the CLASH survey toward this cluster. We convincingly exclude the low-redshift regime of z < 3, for which convoluted critical curves are generated by our method, as the solution bends to accommodate the wide angles of MACS0647-JD for this low redshift. Instead, a best fit to all sets of lensed galaxy positions and redshifts provides a geometric redshift of z≃ 10.8_(-0.4)^(+0.3) for MACS0647-JD, strongly supporting the higher photometric redshift solution. Importantly, we find a tight linear relation between the relative brightnesses of all nine sets of multiply lensed images and their relative magnifications as predicted by our model. This agreement provides a benchmark for the quality of the lens model, and establishes the robustness of our free-form lensing method for measuring model-independent geometric source distances and for deriving objective central cluster mass distributions. After correcting for its magnification the luminosity of MACS0647-JD remains relatively high at M UV = −19.4, which is within a factor of a few in flux of some surprisingly luminous z sime 10–11 candidates discovered recently in Hubble blank field surveys
Geometric Support for Dark Matter by an Unaligned Einstein Ring in Abell 3827
The non-detection of dark matter (DM) particles in increasingly stringent
laboratory searches has encouraged alternative gravity theories where gravity
is sourced only from visible matter. Here, we consider whether such theories
can pass a two-dimensional test posed by gravitational lensing -- to reproduce
a particularly detailed Einstein ring in the core of the galaxy cluster Abell
3827. We find that when we require the lensing mass distribution to strictly
follow the shape (ellipticity and position angle) of the light distribution of
cluster member galaxies, intracluster stars, and the X-ray emitting
intracluster medium, we cannot reproduce the Einstein ring, despite allowing
the mass-to-light ratios of these visible components to freely vary with radius
to mimic alternative gravity theories. Alternatively, we show that the detailed
features of the Einstein ring are accurately reproduced by allowing a smooth,
freely oriented DM halo in the lens model, with relatively small contributions
from the visible components at a level consistent with their observed
brightnesses. This dominant DM component is constrained to have the same
orientation as the light from the intracluster stars, indicating that the
intracluster stars trace the gravitational potential of this component. The
Einstein ring of Abell 3827 therefore presents a new challenge for alternative
gravity theories: not only must such theories find agreement between the total
lensing mass and visible mass, but they must also find agreement between the
projected sky distribution of the lensing mass and that of the visible matter,
a more stringent test than has hitherto been posed by lensing data.Comment: 20 pages, 7 figures, 8 tables. Accepted for publication in Ap
Submillimeter Array Observation of the Proto-Planetary Nebula CRL 618 in the CO J=6-5 Line
We report on the results of a Submillimeter Array interferometric observation
of the proto-planetary nebula CRL 618 in the 12CO J=6-5 line. With the new
capability of SMA enabling us to use two receivers at a time, we also observed
simultaneously in the 12CO J=2-1 and 13CO J=2-1 lines. The 12CO J=6-5 and 13CO
J=2-1 lines were first interferometrically observed toward CRL 618. The flux of
the high velocity component of the 12CO J=6-5 line is almost fully recovered,
while roughly 80% of the flux of the low velocity component is resolved out.
The low recovery rate suggests that the emission region of the low velocity
component of the 12CO J=6-5 line is largely extended. Continuum emission is
detected both at 230 and 690 GHz. The flux of the 690 GHz continuum emission
seems to be partially resolved out, suggesting dust emission partly
contaminates the 690 GHz continuum flux. The cavity structure, which has been
confirmed in a previous observation in the 12CO J=2-1 line, is not clearly
detected in the 12CO J=6-5 line, and only the south wall of the cavity is
detected. This result suggests that the physical condition of the molecular
envelope of CRL 618 is not exactly axial symmetric.Comment: 24 pages, 9 figures, 1 table, accepted for publication in AJ. Full
resolution version available at
http://www.asiaa.sinica.edu.tw/~junichi/paper
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