The CIII and CIV rest-frame UV emission lines are powerful probes of the ionizations states of galaxies. They have furthermore been suggested as alternatives for spectroscopic redshift confirmation ...of objects at the epoch of reionization (\(z>6\)), where the most frequently used redshift indicator, Ly\(\alpha\), is attenuated by the high fraction of neutral hydrogen in the inter-galactic medium. However, currently only very few confirmations of carbon UV lines at these high redshifts exist, making it challenging to quantify these claims. Here, we present the detection of CIV\(\lambda\lambda\)1548,1551\AA\ in \HST\ slitless grism spectroscopy obtained by GLASS of a Ly\(\alpha\) emitter at \(z=6.11\) multiply imaged by the massive foreground galaxy cluster RXJ2248. The CIV emission is detected at the 3--5\(\sigma\) level in two images of the source, with marginal detection in two other images. We do not detect significant CIII\(\lambda\lambda\)1907,1909\AA\ emission implying an equivalent width EW\(_\textrm{CIII}<20\)\AA\ (1\(\sigma\)) and \(\textrm{CIV/CIII}>0.7\) (2\(\sigma\)). Combined with limits on the rest-frame UV flux from the HeII\(\lambda\)1640\AA\ emission line and the OIII\(\lambda\lambda\)1661,1666\AA\ doublet, we put constraints on the metallicity and the ionization state of the galaxy. The estimated line ratios and equivalent widths do not support a scenario where an AGN is responsible for ionizing the carbon atoms. SED fits including nebular emission lines imply a source with a mass of log(M/M\(_\odot)\sim9\), SFR of around 10M\(_\odot\)/yr, and a young stellar population \(<50\)Myr old. The source shows a stronger ionizing radiation field than objects with detected CIV emission at \(z<2\) and adds to the growing sample of low-mass (log(M/M\(_\odot)\lesssim9\)) galaxies at the epoch of reionization with strong radiation fields from star formation.
We use imaging obtained with the Hubble Space Telescope Wide Field Camera 3 to search for z_850 dropouts at z~7 and J_110 dropouts at z~9 lensed by the Bullet Cluster. In total we find 10 z_850 ...dropouts in our 8.27 arcmin^2 field. Using magnification maps from a combined weak and strong lensing mass reconstruction of the Bullet Cluster and correcting for estimated completeness levels, we calculate the surface density and luminosity function of our z_850 dropouts as a function of intrinsic (accounting for magnification) magnitude. We find results consistent with published blank field surveys, despite using much shallower data, and demonstrate the effectiveness of cluster surveys in the search for z~7 galaxies.
In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery ...of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z=0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z=1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.
The TMT Detailed Science Case describes the transformational science that the Thirty Meter Telescope will enable. Planned to begin science operations in 2024, TMT will open up opportunities for ...revolutionary discoveries in essentially every field of astronomy, astrophysics and cosmology, seeing much fainter objects much more clearly than existing telescopes. Per this capability, TMT's science agenda fills all of space and time, from nearby comets and asteroids, to exoplanets, to the most distant galaxies, and all the way back to the very first sources of light in the Universe. More than 150 astronomers from within the TMT partnership and beyond offered input in compiling the new 2015 Detailed Science Case. The contributing astronomers represent the entire TMT partnership, including the California Institute of Technology (Caltech), the Indian Institute of Astrophysics (IIA), the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), the National Astronomical Observatory of Japan (NAOJ), the University of California, the Association of Canadian Universities for Research in Astronomy (ACURA) and US associate partner, the Association of Universities for Research in Astronomy (AURA).
We present evidence for a Spitzer-selected luminous infrared galaxy (LIRG) behind the Bullet Cluster. The galaxy, originally identified in IRAC photometry as a multiply imaged source, has a spectral ...energy distribution consistent with a highly extincted (A_V~3.3), strongly star-forming galaxy at z=2.7. Using our strong gravitational lensing model presented in Bradac et al. (2006), we find that the magnifications are 10 to 50 for the three images of the galaxy. The implied infrared luminosity is consistent with the galaxy being a LIRG, with a stellar mass of M_*~2e11 M_Sun and a star formation rate of ~90 M_Sun/yr. With lensed fluxes at 24 microns of 0.58 mJy and 0.39 mJy in the two brightest images, this galaxy presents a unique opportunity for detailed study of an obscured starburst with star fomation rate comparable to that of L* galaxies at z>2.
We present DLSCL J0916.2+2951 (z=0.53), a newly discovered major cluster merger in which the collisional cluster gas has become dissociated from the collisionless galaxies and dark matter. We ...identified the cluster using optical and weak lensing observations as part of the Deep Lens Survey. Our follow-up observations with Keck, Subaru, Hubble Space Telescope, and Chandra show that the cluster is a dissociative merger and constrain the dark matter self-interaction cross-section {\sigma}_{DM}m_{DM}^{-1}\leq7 cm^2g^{-1}. The system is observed at least 0.7\pm0.2 Gyr since first pass-through, thus providing a picture of cluster mergers 2-5 times further progressed than similar systems observed to date. This improved temporal leverage has implications for our understanding of merging clusters and their impact on galaxy evolution.
(Abridged) We compare recent results from X-ray, strong lensing, weak lensing, and optical observations with numerical simulations of the merging galaxy cluster 1E0657-56. X-ray observations reveal a ...bullet-like subcluster with a prominent bow shock, while lensing results show that the positions of the total mass peaks are consistent with the centroids of the collisionless galaxies (and inconsistent with the X-ray brightness peaks). Previous studies, based on older observational datasets, have placed upper limits on the self-interaction cross-section of dark matter per unit mass, sigma/m, using simplified analytic techniques. In this work, we take advantage of new, higher-quality observational datasets by running N-body simulations of 1E0657-56 that include the effects of self-interacting dark matter, and comparing the results with observations. Furthermore, the recent data allow for a new independent method of constraining sigma/m, based on the non-observation of an offset between the bullet subcluster mass peak and galaxy centroid. This new method places an upper limit (68% confidence) of sigma/m < 1.25 cm^2/g. If we make the assumption that the subcluster and the main cluster had equal mass-to-light ratios prior to the merger, we derive our most stringent constraint of sigma/m < 0.7 cm^2/g, which comes from the consistency of the subcluster's observed mass-to-light ratio with the main cluster's, and with the universal cluster value, ruling out the possibility of a large fraction of dark matter particles being scattered away due to collisions. Our limit is a slight improvement over the previous result from analytic estimates, and rules out most of the 0.5 - 5cm^2/g range invoked to explain inconsistencies between the standard collisionless cold dark matter model and observations.
Lens modeling is the key to successful and meaningful automated strong galaxy-scale gravitational lens detection. We have implemented a lens-modeling "robot" that treats every bright red galaxy (BRG) ...in a large imaging survey as a potential gravitational lens system. Using a simple model optimized for "typical" galaxy-scale lenses, we generate four assessments of model quality that are used in an automated classification. The robot infers the lens classification parameter H that a human would have assigned; the inference is performed using a probability distribution generated from a human-classified training set, including realistic simulated lenses and known false positives drawn from the HST/EGS survey. We compute the expected purity, completeness and rejection rate, and find that these can be optimized for a particular application by changing the prior probability distribution for H, equivalent to defining the robot's "character." Adopting a realistic prior based on the known abundance of lenses, we find that a lens sample may be generated that is ~100% pure, but only ~20% complete. This shortfall is due primarily to the over-simplicity of the lens model. With a more optimistic robot, ~90% completeness can be achieved while rejecting ~90% of the candidate objects. The remaining candidates must be classified by human inspectors. We are able to classify lens candidates by eye at a rate of a few seconds per system, suggesting that a future 1000 square degree imaging survey containing 10^7 BRGs, and some 10^4 lenses, could be successfully, and reproducibly, searched in a modest amount of time. Abridged
Astrophys.J.648:L109-L113,2006 We present new weak lensing observations of 1E0657-558 (z=0.296), a unique
cluster merger, that enable a direct detection of dark matter, independent of
assumptions ...regarding the nature of the gravitational force law. Due to the
collision of two clusters, the dissipationless stellar component and the
fluid-like X-ray emitting plasma are spatially segregated. By using both
wide-field ground based images and HST/ACS images of the cluster cores, we
create gravitational lensing maps which show that the gravitational potential
does not trace the plasma distribution, the dominant baryonic mass component,
but rather approximately traces the distribution of galaxies. An 8-sigma
significance spatial offset of the center of the total mass from the center of
the baryonic mass peaks cannot be explained with an alteration of the
gravitational force law, and thus proves that the majority of the matter in the
system is unseen.
Astrophys.J.652:937-947,2006 The galaxy cluster 1E0657-56 (z = 0.296) is remarkably well-suited for
addressing outstanding issues in both galaxy evolution and fundamental physics.
We present a ...reconstruction of the mass distribution from both strong and weak
gravitational lensing data. Multi-color, high-resolution HST ACS images allow
detection of many more arc candidates than were previously known, especially
around the subcluster. Using the known redshift of one of the multiply imaged
systems, we determine the remaining source redshifts using the predictive power
of the strong lens model. Combining this information with shape measurements of
"weakly" lensed sources, we derive a high-resolution, absolutely-calibrated
mass map, using no assumptions regarding the physical properties of the
underlying cluster potential. This map provides the best available
quantification of the total mass of the central part of the cluster. We also
confirm the result from Clowe et al. (2004,2006a).
