251 research outputs found
Flashlights: Properties of Highly Magnified Images Near Cluster Critical Curves in the Presence of Dark Matter Subhalos
Dark matter subhalos with extended profiles and density cores, and globular
stars clusters of mass , that live near the critical curves
in galaxy cluster lenses can potentially be detected through their lensing
magnification of stars in background galaxies. In this work we study the effect
such subhalos have on lensed images, and compare to the case of more well
studied microlensing by stars and black holes near critical curves. We find
that the cluster density gradient and the extended mass distribution of
subhalos are important in determining image properties. Both lead to an
asymmetry between the image properties on the positive and negative parity
sides of the cluster that is more pronounced than in the case of microlensing.
For example, on the negative parity side, subhalos with cores larger than about
pc do not generate any images with magnification above outside
of the immediate vicinity of the cluster critical curve. We discuss these
factors using analytical and numerical analysis, and exploit them to identify
observable signatures of subhalos: subhalos create pixel-to-pixel flux
variations of magnitudes, on the positive parity side of
clusters. These pixels tend to cluster around (otherwise invisible) subhalos.
Unlike in the case of microlensing, signatures of subhalo lensing can be found
up to away from the critical curves of massive clusters.Comment: ApJ, submitted, 21 pages, 17 figure
A search for transients in the Reionization Lensing Cluster Survey (RELICS): Three new supernovae
The Reionization Cluster Survey (RELICS) imaged 41 galaxy clusters with the
Hubble Space Telescope (HST), in order to detect lensed and high-redshift
galaxies. Each cluster was imaged to about 26.5 AB mag in three optical and
four near-infrared bands, taken in two distinct visits separated by varying
time intervals. We make use of the multiple near-infrared epochs to search for
transient sources in the cluster fields, with the primary motivation of
building statistics for bright caustic crossing events in gravitational arcs.
Over the whole sample, we do not find any significant ()
caustic crossing events, in line with expectations from semi-analytic
calculations but in contrast to what may be naively expected from previous
detections of some bright events, or from deeper transient surveys that do find
high rates of such events. Nevertheless, we find six prominent supernova (SN)
candidates over the 41 fields: three of them were previously reported and three
are new ones reported here for the first time. Out of the six candidates, four
are likely core-collapse (CC) SNe -- three in cluster galaxies, and among which
only one was known before, and one slightly behind the cluster at
. The other two are likely Ia -- both of them previously known,
one probably in a cluster galaxy, and one behind it at . Our study
supplies empirical bounds for the rate of caustic crossing events in galaxy
cluster fields to typical HST magnitudes, and lays the groundwork for a future
SN rate study.Comment: Accepted for publication in MNRAS. 10 pages, 3 figure
Unscrambling the lensed galaxies in JWST images behind SMACS0723
The first deep field images from the James Webb Space Telescope (JWST) of the
galaxy cluster SMACS~J0723.3-7327 reveal a wealth of new lensed images at
uncharted infrared wavelengths, with unprecedented depth and resolution. Here
we securely identify 14 new sets of multiply imaged galaxies totalling 42
images, adding to the five sets of bright and multiply-imaged galaxies already
known from Hubble Space Telescope data. We find examples of arcs crossing
critical curves, allowing detailed community follow-up, such as JWST
spectroscopy for precise redshift determinations, and measurements of the
chemical abundances and of the detailed internal gas dynamics of very distant,
young galaxies. One such arc contains compact knots of magnification
750, and features a microlensed transient. We also detect an Einstein
cross candidate only visible thanks to JWST's superb resolution. Our parametric
lens model is available at
https://www.dropbox.com/sh/gwup2lvks0jsqe5/AAC2RRSKce0aX-lIFCc9vhBXa?dl=0 , and
will be regularly updated using additional spectroscopic redshifts. The model
reproduces the multiple images to better than an rms of ,
and allows for accurate magnification estimates of high-redshift galaxies. The
intracluster light extends beyond the cluster members, exhibiting large-scale
features that suggest a significant past dynamical disturbance. This work
represents a first taste of the enhanced power JWST will have for
lensing-related science.Comment: Submitted to ApJ. 13 pages, 6 figure
Oral prehabilitation for patients with head and neck cancer:getting it right - the Restorative Dentistry-UK consensus on a multidisciplinary approach to oral and dental assessment and planning prior to cancer treatment
Historically, oral and dental issues for head and neck cancer patients were often not considered until after cancer treatment was complete. As a result, outcomes for oral rehabilitation were sometimes suboptimal. Inconsistencies in service delivery models and qualification, training and experience of staff delivering dental care often compounded this problem, making research and audit almost impossible. Collaborative working by consultants in restorative dentistry from all over the UK as part of a Restorative Dentistry-UK (RD UK) subgroup, renamed more recently as the RD-UK Head and Neck Cancer Clinical Excellence Network (CEN), has re-emphasised the importance of specialist restorative dentistry intervention at the outset of the head and neck cancer pathway to optimise outcomes of patient care. The CEN has driven several initiatives, reflecting Getting It Right First Time (GIRFT) principles aimed at reducing unwarranted variation. This improved consistency in approach and optimised collaborative working of the team now presents a better environment for multicentre audit and research. Ultimately, this should result in a continued improvement in patient and carer experience
Flashlights: an off-caustic lensed star at redshift z = 1.26 in Abell 370
We report the discovery of a transient seen in a strongly lensed arc at redshift zs = 1.2567 in Hubble Space Telescope imaging of the Abell 370 galaxy cluster. The transient is detected at 29.51 ± 0.14 AB mag in a WFC3/UVIS F200LP difference image made using observations from two different epochs, obtained in the framework of the Flashlights programme, and is also visible in the F350LP band (mF350LP ≈ 30.53 ± 0.76 AB mag). The transient is observed on the negative-parity side of the critical curve at a distance of ∼0.6 arcsec from it, greater than previous examples of lensed stars. The large distance from the critical curve yields a significantly smaller macromagnification, but our simulations show that bright, O/B-type supergiants can reach sufficiently high magnifications to be seen at the observed position and magnitude. In addition, the observed transient image is a trailing image with an observer-frame time delay of ∼+0.8 d from its expected counterpart, so that any transient lasting for longer than that should have also been seen on the minima side and is thus excluded. This, together with the blue colour we measure for the transient (mF200LP − mF350LP ≈ [−0.3, −1.6] AB), rules out most other transient candidates such as (kilo)novae, for example, and makes a lensed star the prime candidate. Assuming that the transient is indeed a lensed star as suggested, many more such events should be detected in the near future in cluster surveys with the Hubble Space Telescope and JWST.This research was supported by NASA/HST grants GO-15936 and GO-16278 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. AKM, AZ, and MG acknowledge support by grant 2020750 from the United States-Israel Binational Science Foundation (BSF) and grant 2109066 from the United States National Science Foundation (NSF), and by the Ministry of Science & Technology, Israel. This work was supported by JSPS KAKENHI grants JP22H01260, JP20H05856, and JP20H00181. AKM would like to thank Lukas Furtak for useful discussions. JMD acknowledges the support of projects PGC2018-101814-B-100 and MDM-2017-0765. AVF is grateful for additional financial support from the Christopher R. Redlich Fund and numerous individual donors.Peer reviewe
Flashlights: More than A Dozen High-Significance Microlensing Events of Extremely Magnified Stars in Galaxies at Redshifts z=0.7-1.5
Once only accessible in nearby galaxies, we can now study individual stars
across much of the observable universe aided by galaxy-cluster gravitational
lenses. When a star, compact object, or multiple such objects in the foreground
galaxy-cluster lens become aligned, they can magnify a background individual
star, and the timescale of a magnification peak can limit its size to tens of
AU. The number and frequency of microlensing events therefore opens a window
into the population of stars and compact objects, as well as high-redshift
stars. To assemble the first statistical sample of stars in order to constrain
the initial mass function (IMF) of massive stars at redshift z=0.7-1.5, the
abundance of primordial black holes in galaxy-cluster dark matter, and the IMF
of the stars making up the intracluster light, we are carrying out a 192-orbit
program with the Hubble Space Telescope called "Flashlights," which is now
two-thirds complete owing to scheduling challenges. We use the ultrawide F200LP
and F350LP long-pass WFC3 UVIS filters and conduct two 16-orbit visits
separated by one year. Having an identical roll angle during both visits, while
difficult to schedule, yields extremely clean subtraction. Here we report the
discovery of more than a dozen bright microlensing events, including multiple
examples in the famous "Dragon Arc" discovered in the 1980s, as well as the
"Spocks" and "Warhol" arcs that have hosted already known supergiants. The
ultradeep observer-frame ultraviolet-through-optical imaging is sensitive to
hot stars, which will complement deep James Webb Space Telescope infrared
imaging. We are also acquiring Large Binocular Telescope LUCI and Keck-I
MOSFIRE near-infrared spectra of the highly magnified arcs to constrain their
recent star-formation histories
BUFFALO/Flashlights: Constraints on the abundance of lensed supergiant stars in the Spock galaxy at redshift 1
In this work, we present a constraint on the abundance of supergiant (SG) stars at redshift z ≈ 1, based on recent observations of astrongly lensed arc at this redshift. First we derived a free-form model of MACS J0416.1-2403 using data from the Beyond Ultradeep Frontier Fields and Legacy Observations (BUFFALO) program. The new lens model is based on 72 multiply lensed galaxies thatproduce 214 multiple images, making it the largest sample of spectroscopically confirmed lensed galaxies on this cluster. The largercoverage in BUFFALO allowed us to measure the shear up to the outskirts of the cluster, and extend the range of lensing constraintsup to ∼1 Mpc from the central region, providing a mass estimate up to this radius. As an application, we make predictions for thenumber of high-redshift multiply lensed galaxies detected in future observations with the James Webb Space Telescope (JWST).Then we focus on a previously known lensed galaxy at z = 1.0054, nicknamed Spock, which contains four previously reportedtransients. We interpret these transients as microcaustic crossings of SG stars and explain how we computed the probability of suchevents. Based on simplifications regarding the stellar evolution, we find that microlensing (by stars in the intracluster medium) ofSG stars at z = 1.0054 can fully explain these events. The inferred abundance of SG stars is consistent with either (1) a numberdensity of stars with bolometric luminosities beyond the Humphreys-Davidson (HD) limit (Lmax ≈ 6 × 105 L for red stars), whichis below ∼400 stars kpc−2, or (2) the absence of stars beyond the HD limit but with a SG number density of ∼9000 kpc−2 for starswith luminosities between 105 L and 6 × 105 L. This is equivalent to one SG star per 10 × 10 pc2. Finally, we make predictions forfuture observations with JWST’s NIRcam. We find that in observations made with the F200W filter that reach 29 mag AB, if cool red SG stars exist at z ≈ 1 beyond the HD limit, they should be easily detected in this arc
BUFFALO/Flashlights: Constraints on the abundance of lensed supergiant stars in the Spock galaxy at redshift 1
We present a constraint on the abundance of supergiant (SG) stars at redshift
z approx. 1, based on recent observations of a strongly lensed arc at this
redshift. First we derive a free-form model of MACS J0416.1-2403 using data
from the BUFFALO program. The new lens model is based on 72 multiply lensed
galaxies that produce 214 multiple images, making it the largest sample of
spectroscopically confirmed lensed galaxies on this cluster. The larger
coverage in BUFFALO allows us to measure the shear up to the outskirts of the
cluster, and extend the range of lensing constraints up to ~ 1 Mpc from the
central region, providing a mass estimate up to this radius. As an application,
we make predictions for the number of high-redshift multiply-lensed galaxies
detected in future observations with JWST. Then we focus on a previously known
lensed galaxy at z=1.0054, nicknamed Spock, which contains four previously
reported transients. We interpret these transients as microcaustic crossings of
SG stars and compute the probability of such events. Based on simplifications
regarding the stellar evolution, we find that microlensing (by stars in the
intracluster medium) of SG stars at z=1.0054 can fully explain these events.
The inferred abundance of SG stars is consistent with either (1) a number
density of stars with bolometric luminosities beyond the Humphreys-Davidson
(HD) limit (L ~ ) that is below 400 stars per sq. kpc,
or (2) the absence of stars beyond the HD limit but with a SG number density of
~ 9000 per sq. kpc for stars with luminosities between and
. This is equivalent to one SG star per 10x10 pc. We finally
make predictions for future observations with JWST's NIRcam. We find that in
observations made with the F200W filter that reach 29 mag AB, if cool red SG
stars exist at z~1 beyond the HD limit, they should be easily detected in this
arcComment: 24 pages & 18 figure
JWST's PEARLS: a new lens model for ACT-CL J01024915, "EL Gordo'', and the first red supergiant star at cosmological distances discovered by JWST
The first JWST data on the massive colliding cluster El Gordo confirm 23
known families of multiply lensed images and identify 8 new members of these
families. Based on these families, which have been confirmed spectroscopically
by MUSE, we derived an initial lens model. This model guided the identification
of 37 additional families of multiply lensed galaxies, among which 28 are
entirely new systems, and 9 were previously known. The initial lens model
determined geometric redshifts for the 37 new systems. The geometric redshifts
agree reasonably well with spectroscopic or photometric redshifts when those
are available. The geometric redshifts enable two additional models that
include all 60 families of multiply lensed galaxies spanning a redshift range
. The derived dark-matter distribution confirms the double-peak
configuration of mass found by earlier work with the southern and northern
clumps having similar masses. We confirm that El Gordo is the most massive
known cluster at and has an estimated virial mass close the maximum
mass allowed by standard cosmological models. The JWST images also reveal the
presence of small-mass perturbers that produce small lensing distortions. The
smallest of these is consistent with being a dwarf galaxy at and has
an estimated mass of ~\Msol, making it the smallest substructure
found at . The JWST images also show several candidate caustic-crossing
events. One of them is detected at high significance at the expected position
of the critical curve and is likely a red supergiant star at . This
would be the first red supergiant found at cosmological distances. The cluster
lensing should magnify background objects at , making more of them visible
than in blank fields of similar size, but there appears to be a deficiency of
such objects.Comment: 27 pages, 21 figure
Reaching for the stars – JWST/NIRSpec spectroscopy of a lensed star candidate at z = 4.76
We present JWST/NIRSpec observations of a highly magnified star candidate at a photometric redshift of zphot ≃ 4.8, previously detected in JWST/NIRCam imaging of the strong lensing (SL) cluster MACS J0647+7015 (z = 0.591). The spectroscopic observation allows us to precisely measure the redshift of the host arc at zspec = 4.758 ± 0.004, and the star’s spectrum displays clear Lyman- and Balmer-breaks commensurate with this redshift. A fit to the spectrum suggests a B-type super-giant star of surface temperature K with either a redder F-type companion ( K) or significant dust attenuation (AV ≃ 0.82) along the line of sight. We also investigate the possibility that this object is a magnified young globular cluster rather than a single star. We show that the spectrum is in principle consistent with a star cluster, which could also accommodate the lack of flux variability between the two epochs. However, the lack of a counter image and the strong upper limit on the size of the object from lensing symmetry, r ≲ 0.5 pc, could indicate that this scenario is somewhat less likely – albeit not completely ruled out by the current data. The presented spectrum seen at a time when the Universe was only ∼1.2 Gyr old showcases the ability of JWST to study early stars through extreme lensing
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