Maruša Bradač

Evidence of the accelerated expansion of the Universe from weak lensing tomography with COSMOS

We present a comprehensive analysis of weak gravitational lensing by large-scale structure in the Hubble Space Telescope Cosmic Evolution Survey (COSMOS), in which we combine space-based galaxy shape measurements with ground-based photometric redshifts to study the redshift dependence of the lensing signal and constrain cosmological parameters. After applying our weak lensing-optimized data reduction, principal-component interpolation for the spatially, and temporally varying ACS point-spread function, and improved modelling of charge-transfer inefficiency, we measured a lensing signal that is consistent with pure gravitational modes and no significant shape systematics. We carefully estimated the statistical uncertainty from simulated COSMOS-like fields obtained from ray-tracing through the Millennium Simulation, including the full non-Gaussian sampling variance. We tested our lensing pipeline on simulated space-based data, recalibrated non-linear power spectrum corrections using the ray-tracing analysis, employed photometric redshift information to reduce potential contamination by intrinsic galaxy alignments, and marginalized over systematic uncertainties. We find that the weak lensing signal scales with redshift as expected from general relativity for a concordance ACDM cosmology, including the full cross-correlations between different redshift bins. Assuming a flat ACDM cosmology, we measure σ 8 (Ω m /0.3) 0.51 = 0.75 ± 0.08 from lensing, in perfect agreement with WMAP-5, yielding joint constraints Ω m = 0.266 +0.025 -0.023 σ 8 = 0.802 +0.028 -0.029 (all 68.3% conf.). Dropping the assumption of flatness and using priors from the HST Key Project and Big-Bang nucleosynthesis only, we find a negative deceleration parameter q 0 at 94.3% confidence from the tomographic lensing analysis, providing independent evidence of the accelerated expansion of the Universe. For a flat ωCDM cosmology and prior ω ∈ [-2, 0], we obtain ω < -0.41 (90% conf.). Our dark energy constraints are still relatively weak solely due to the limited area of COSMOS. However, they provide an important demonstration of the usefulness of tomographic weak lensing measurements from space.

New Observations of z ~ 7 Galaxies: Evidence for a Patchy Reionization

We present new results from our search for z ~ 7 galaxies from deep spectroscopic observations of candidate z dropouts in the CANDELS fields. Despite the extremely low flux limits achieved by our sensitive observations, only two galaxies have robust redshift identifications, one from its Lyα emission line at z = 6.65, the other from its Lyman break, i.e., the continuum discontinuity at the Lyα wavelength consistent with a redshift of 6.42 but with no emission line. In addition, for 23 galaxies we present deep limits in the Lyα equivalent width derived from the nondetections in ultradeep observations. Using this new data as well as previous samples, we assemble a total of 68 candidate z ~ 7 galaxies with deep spectroscopic observations, of which 12 have a line detection. With this much enlarged sample we can place solid constraints on the declining fraction of Lyα emission in z ~ 7 Lyman-break galaxies compared to z ~ 6, both for bright and faint galaxies. Applying a simple analytical model, we show that the present data favor a patchy reionization process rather than a smooth one.

Multiple images of a highly magnified supernova formed by an early-type cluster galaxy lens

Finding four for the light of one Seeing double may cause concern for some, but seeing quadruple? Its just what astronomers have been hoping for. Kelly et al. have now detected four images of the same distant supernova with the sharp eye of a space telescope. The supernova shines brightly from the arm of a spiral galaxy that lies far beyond another galaxy between it and us. This intervening galaxy is massive enough to bend the light from the supernova and its host galaxy into multiple images. This behavior relies on the curvature of spacetime and will provide insight into the luminous and dark matter in the lensing galaxy. Science, this issue p. 1123 Light from a distant supernova at z = 1.491 is detected in four images after being deflected en route by gravitational forces. 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 grism lens-amplified survey from space (glass). i. survey overview and first data release

We give an overview of the Grism Lens Amplified Survey from Space (GLASS), a large Hubble Space Telescope program aimed at obtaining grism spectroscopy of the fields of ten massive clusters of galaxies at redshift z=0.308-0.686, including the Hubble Frontier Fields (HFF). The Wide Field Camera 3 yields near infrared spectra of the cluster cores, covering the wavelength range 0.81-1.69mum through grisms G102 and G141, while the Advanced Camera for Surveys in parallel mode provides G800L spectra of the infall regions of the clusters. The WFC3 spectra are taken at two almost orthogonal position angles in order to minimize the effects of confusion. After summarizing the scientific drivers of GLASS, we describe the sample selection as well as the observing strategy and data processing pipeline. We then utilize MACSJ0717.5+3745, a HFF cluster and the first one observed by GLASS, to illustrate the data quality and the high-level data products. Each spectrum brighter than H_AB=23 is visually inspected by at least two co-authors and a redshift is measured when sufficient information is present in the spectra. Furthermore, we conducted a thorough search for emission lines through all the GLASS WFC3 spectra with the aim of measuring redshifts for sources with continuum fainter than H_AB=23. We provide a catalog of 139 emission-line based spectroscopic redshifts for extragalactic sources, including three new redshifts of multiple image systems (one probable, two tentative). In addition to the data itself we also release software tools that are helpful to navigate the data.

DISCOVERY OF A DISSOCIATIVE GALAXY CLUSTER MERGER WITH LARGE PHYSICAL SEPARATION

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 (DM). 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 DM self-interaction cross-section σDM m –1 DM 7 cm2 g–1. The system is observed at least 0.7 ± 0.2 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.

Through the Looking GLASS: HST Spectroscopy of Faint Galaxies Lensed by the Frontier Fields Cluster MACSJ0717.5+3745

The Grism Lens-Amplified Survey from Space (GLASS) is a Hubble Space Telescope (HST) Large Program, which will obtain 140 orbits of grism spectroscopy of the core and infall regions of 10 galaxy clusters, selected to be among the very best cosmic telescopes. Extensive HST imaging is available from many sources including the CLASH and Frontier Fields programs. We introduce the survey by analyzing spectra of faint multiply-imaged galaxies and z ≳ 6 galaxy candidates obtained from the first 7 orbits out of 14 targeting the core of the Frontier Fields cluster MACSJ0717.5+3745. Using the G102 and G141 grisms to cover the wavelength range 0.8-1.7 μm, we confirm four strongly lensed systems by detecting emission lines in each of the images. For the 9 z ≳ 6 galaxy candidates clear from contamination, we do not detect any emission lines down to a 7 orbit 1σ noise level of ∼5 × 10 -18 erg s-1 cm-2. Taking lensing magnification into account, our flux sensitivity reaches ∼0.2-5 × 10-18 erg s-1cm-2. These limits over an uninterrupted wavelength range rule out the possibility that the high-z galaxy candidates are instead strong line emitters at lower redshift. These results show that by means of careful modeling of the background - and with the assistance of lensing magnification - interesting flux limits can be reached for large numbers of objects, avoiding pre-selection and the wavelength restrictions inherent to ground-based multi-slit spectroscopy. These observations confirm the power of slitless HST spectroscopy even in fields as crowded as a cluster core.

FOCUSING COSMIC TELESCOPES: EXPLORING REDSHIFT z ∼ 5-6 GALAXIES WITH THE BULLET CLUSTER 1E0657 – 56*

The gravitational potential of clusters of galaxies acts as a cosmic telescope allowing us to find and study galaxies at fainter limits than otherwise possible and thus probe closer to the epoch of formation of the first galaxies. We use the Bullet cluster 1E0657 – 56 (z = 0.296) as a case study, because its high mass and merging configuration makes it one of the most efficient cosmic telescopes we know. We develop a new algorithm to reconstruct the gravitational potential of the Bullet cluster based on a non-uniform adaptive grid, combining strong and weak gravitational lensing data derived from deep Hubble Space Telescope/Advanced Camera for Surveys F606W–F775W–F850LP and ground-based imaging. We exploit this improved mass map to study z ~ 5-6 Lyman break galaxies (LBGs), which we detect as dropouts. One of the LBGs is multiply imaged, providing a geometric confirmation of its high redshift, and is used to further improve our mass model. We quantify the uncertainties in the magnification map reconstruction in the intrinsic source luminosity, and in the volume surveyed, and show that they are negligible compared to sample variance when determining the luminosity function of high-redshift galaxies. With shallower and comparable magnitude limits to Hubble Ultra Deep Field (HUDF) and Great Observatories Origins Deep Survey (GOODS), the Bullet cluster observations, after correcting for magnification, probe deeper into the luminosity function of the high-redshift galaxies than GOODS and only slightly shallower than HUDF. We conclude that accurately focused cosmic telescopes are the most efficient way to sample the bright end of the luminosity function of high-redshift galaxies and—in case they are multiply imaged—confirm their redshifts.

THE GRISM LENS-AMPLIFIED SURVEY FROM SPACE (GLASS). III. A CENSUS OF Lyα EMISSION AT z ≳ 7 FROM HST SPECTROSCOPY

Draft version November 16, 2015 Preprint typeset using L A TEX style emulateapj v. 5/2/11 THE GRISM LENS-AMPLIFIED SURVEY FROM SPACE (GLASS). III. A CENSUS OF Lyα EMISSION AT z & 7 FROM HST SPECTROSCOPY ˇ 4 , B. Vulcani 5 , K.-H., Huang 4 , A. Hoag 4 , M. Maseda 6 L. Guaita 7 K. B. Schmidt 1,2 , T. Treu 3 , M. Brada c L. Pentericci 7 , G. B. Brammer 8 , M. Dijkstra 9 , A. Dressler 10 A. Fontana 7 , A. L. Henry 11 , T. A. Jones 1 , C. Mason 1 , M. Trenti 12 , X. Wang 1 , 1 Department of Physics, University of California, Santa Barbara, CA, 93106-9530, USA Leibniz-Institut f¨ ur Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany 3 Department of Physics and Astronomy, UCLA, Los Angeles, CA, 90095-1547, USA 4 Department of Physics, University of California, Davis, CA, 95616, USA Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, the University of Tokyo, Kashiwa, 277-8582, Japan 6 Max-Planck-Institut f¨ ur Astronomie, K¨ onigstuhl 17, D-69117 Heidelberg, Germany 7 INAF - Osservatorio Astronomico di Roma Via Frascati 33 - 00040 Monte Porzio Catone, I 8 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA 9 Institute of Theoretical Astrophysics, University of Oslo, Postboks 1029, 0858 Oslo, Norway 10 The Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA 11 Astrophysics Science Division, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 and 12 School of Physics, The University of Melbourne, VIC, 3010 Australia Draft version November 16, 2015 arXiv:1511.04205v1 [astro-ph.GA] 13 Nov 2015 ABSTRACT We present a census of Lyα emission at z & 7 utilizing deep near infrared HST grism spectroscopy from the first six completed clusters of the Grism Lens-Amplified Survey from Space (GLASS). In 24/159 photometrically selected galaxies we detect emission lines consistent with Lyα in the GLASS spectra. Based on the distribution of signal-to-noise ratios and on simulations we expect the com- pleteness and the purity of the sample to be 40-100% and 60-90%, respectively. For the objects without detected emission lines we show that the observed (not corrected for lensing magnification) 1σ flux limits reaches 5 × 10 −18 erg/s/cm 2 per position angle over the full wavelength range of GLASS (0.8–1.7µm). Based on the conditional probability of Lyα emission measured from the ground at z ∼ 7 we would have expected 12-18 Lyα emitters. This is consistent with the number of detections, within the uncertainties, confirming the drop in Lyα emission with respect to z ∼ 6. Deeper follow-up spectroscopy, here exemplified by Keck spectroscopy, is necessary to improve our estimates of com- pleteness and purity, and to confirm individual candidates as true Lyα emitters. These candidates include a promising source at z = 8.1. The spatial extent of Lyα in a deep stack of the most convincing Lyα emitters with hzi = 7.2 is consistent with that of the rest-frame UV continuum. Extended Lyα emission, if present, has a surface brightness below our detection limit, consistent with the properties of lower redshift comparison samples. From the stack we estimate upper limits on rest-frame UV emission line ratios and find f CIV /f Lyα . 0.32 and f CIII] /f Lyα . 0.23 in good agreement with other values published in the literature. Subject headings: galaxies: high-redshift – techniques: spectroscopic – methods: data analysis 1. INTRODUCTION With the deployment of the wide field camera 3 (WFC3) on the Hubble Space Telescope (HST ) in 2009, the samples of galaxies at the epoch of reionization, the phase-transition from a completely neutral inter-galactic medium (IGM) to a fully ionized IGM at z & 6, have grown dramatically. One of the main results of the WFC3 imaging campaigns has been the accurate deter- mination of the luminosity function of star forming high- redshift (based on their photometry) Lyman break galax- ies (e.g. Bouwens et al. 2015b; Finkelstein et al. 2015b). The UV luminosity functions of Lyman break galaxies have provided key constraints on the physics of reioniza- tion (e.g. Robertson et al. 2013; Schmidt et al. 2014a; Duffy et al. 2014). For example, it is clear that the pop- ulation of galaxies that has been detected so far cannot produce enough hard photons to keep the universe ion- ized. However, the luminosity function is found to have kbschmidt@aip.de a steep faint end slope (approximately φ ∝ L −2 ). Thus, faint galaxies could in principle provide enough ionizing photons (Bouwens et al. 2015a; Robertson et al. 2015; Barone-Nugent et al. 2015; Dressler et al. 2015). even though a contribution from AGN might end up being necessary (Madau & Haardt 2015; Giallongo et al. 2015). Also ground based spectroscopic follow-up of photo- metrically selected high-redshift candidates has been an important part of these studies and has provided addi- tional clues about the reionization epoch. Remarkably, only a handful of sources have been confirmed above red- shift 7 (Vanzella et al. 2011; Schenker et al. 2012, 2014; Ono et al. 2012; Finkelstein et al. 2013; Oesch et al. 2015; Roberts-Borsani et al. 2015; Zitrin et al. 2015b). The low probability of detecting Lyα in Lyman break galaxies, could be interpreted as the result of an increased optical depth in the IGM due to a significant fraction of neutral hydrogen. Thus the decline in detected Lyα is poten- tially a “smoking gun” of reionization (Fontana et al. 2010). The conditional probability of Lyα emission for

THE GRISM LENS-AMPLIFIED SURVEY FROM SPACE (GLASS). IV. MASS RECONSTRUCTION OF THE LENSING CLUSTER ABELL 2744 FROM FRONTIER FIELD IMAGING AND GLASS SPECTROSCOPY

We present a strong and weak lensing reconstruction of the massive cluster Abell 2744, the first cluster for which deep Hubble Frontier Field (HFF) images and spectroscopy from the Grism Lens-Amplified Survey from Space (GLASS) are available. By performing a targeted search for emission lines in multiply imaged sources using the GLASS spectra, we obtain 5 high-confidence spectroscopic redshifts and 2 tentative ones. We confirm 1 strongly lensed system by detecting the same emission lines in all 3 multiple images. We also search for additional line emitters blindly and use the full GLASS spectroscopic catalog to test reliability of photometric redshifts for faint line emitters. We see a reasonable agreement between our photometric and spectroscopic redshift measurements, when including nebular emission in photometric redshift estimations. We introduce a stringent procedure to identify only secure multiple image sets based on colors, morphology, and spectroscopy. By combining 7 multiple image systems with secure spectroscopic redshifts (at 5 distinct redshift planes) with 18 multiple image systems with secure photometric redshifts, we reconstruct the gravitational potential of the cluster pixellated on an adaptive grid, using a total of 72 images. The resulting mass map is compared with a stellar mass map obtained from the deep Spitzer Frontier Fields data to study the relative distribution of stars and dark matter in the cluster. We find that the stellar to total mass ratio varies substantially across the cluster field, suggesting that stars do not trace exactly the total mass in this interacting system. The maps of convergence, shear, and magnification are made available in the standard HFF format.

WEAK-LENSING RESULTS FOR THE MERGING CLUSTER A1758*

Here we present the weak-lensing results for A1758, which is known to consist of four subclusters undergoing two separate mergers, A1758N and A1758S. Weak-lensing results for A1758N agree with previous weak-lensing results for clusters 1E0657-558 (Bullet cluster) and MACS J0025.4-1222, whose X-ray gas components were found to be largely separated from their clusters’ gravitational potentials. A1758N has a geometry that is different from previously published mergers in that one of its X-ray peaks overlays the corresponding gravitational potential and the other X-ray peak is well separated from its cluster’s gravitational potential. The weak-lensing mass peaks of the two northern clusters are separated at the 2.5σ level. We estimate the combined mass of the clusters in A1758N to