Kasper B. Schmidt

THE CHANGING Lyα OPTICAL DEPTH IN THE RANGE 6 < z < 9 FROM THE MOSFIRE SPECTROSCOPY OF Y-DROPOUTS

We present MOSFIRE spectroscopy of 13 candidate z∼ 8 galaxies selected as Y-dropouts as part of the BoRG pure parallel survey. We detect no significant Ly α emission (our median 1 σ rest frame equivalent width sensitivity is in the range 2-16̊ A). Using the Bayesian framework derived in a previous paper , w perform a rigorous analysis of a statistical subsample of non-detec tions for ten Y-dropouts, including data from the literature, to study the cosmic evolution of the Ly α emission of Lyman Break Galaxies. We find that Ly α emission is suppressed at z∼ 8 by at least a factor of three with respect to z∼ 6 continuing the downward trend found by previous studies of z-dropouts at z∼ 7. This finding suggests a dramatic evolution in the conditio ns f the intergalactic or circumgalactic media in just 300 Myrs, consistent with the onset of reionization or changes in the physical conditions of the first generations of starfo rming regions. Subject headings: galaxies: evolution — galaxies: high-redshiftWe present the MOSFIRE spectroscopy of 13 candidate z ~ 8 galaxies selected as Y-dropouts as part of the Brightest of Reionization Galaxies pure parallel survey. We detect no significant Ly? emission (our median 1? rest-frame equivalent width sensitivity is in the range 2-16 ?). Using the Bayesian framework derived in a previous paper, we perform a rigorous analysis of a statistical subsample of non-detections for 10 Y-dropouts, including data from the literature, to study the cosmic evolution of the Ly? emission of Lyman break galaxies. We find that Ly? emission is suppressed at z ~ 8 by at least a factor of three with respect to z ~ 6 continuing the downward trend found by previous studies of z-dropouts at z ~ 7. This finding suggests a dramatic evolution in the conditions of the intergalactic or circumgalactic media in just 300?Myr, consistent with the onset of reionization or changes in the physical conditions of the first generations of star-forming regions.

SELECTING QUASARS BY THEIR INTRINSIC VARIABILITY

We present a new and simple technique for selecting extensive, complete, and pure quasar samples, based on their intrinsic variability. We parameterize the single-band variability by a power-law model for the light-curve structure function, with amplitude A and power-law index γ. We show that quasars can be efficiently separated from other non-variable and variable sources by the location of the individual sources in the A-γ plane. We use ~60 epochs of imaging data, taken over ~5 years, from the SDSS stripe 82 (S82) survey, where extensive spectroscopy provides a reference sample of quasars, to demonstrate the power of variability as a quasar classifier in multi-epoch surveys. For UV-excess selected objects, variability performs just as well as the standard SDSS color selection, identifying quasars with a completeness of 90% and a purity of 95%. In the redshift range 2.5 < z < 3, where color selection is known to be problematic, variability can select quasars with a completeness of 90% and a purity of 96%. This is a factor of 5-10 times more pure than existing color selection of quasars in this redshift range. Selecting objects from a broad griz color box without u-band information, variability selection in S82 can afford completeness and purity of 92%, despite a factor of 30 more contaminants than quasars in the color-selected feeder sample. This confirms that the fraction of quasars hidden in the stellar locus of color space is small. To test variability selection in the context of Pan-STARRS 1 (PS1) we created mock PS1 data by down-sampling the S82 data to just six epochs over 3 years. Even with this much sparser time sampling, variability is an encouragingly efficient classifier. For instance, a 92% pure and 44% complete quasar candidate sample is attainable from the above griz-selected catalog. Finally, we show that the presented A-γ technique, besides selecting clean and pure samples of quasars (which are stochastically varying objects), is also efficient at selecting (periodic) variable objects such as RR Lyrae.

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.

First results from the 3D-HST survey: The striking diversity of massive galaxies at z > 1

We present first results from the 3D-HST program, a near-IR spectroscopic survey performed with the Wide Field Camera 3 (WFC3) on the HST. We have used 3D-HST spectra to measure redshifts and Hα equivalent widths (EWHα) for a complete, stellar mass-limited sample of 34 galaxies at 1 10^(11) M_☉ in the COSMOS, GOODS, and AEGIS fields. We find that a substantial fraction of massive galaxies at this epoch are forming stars at a high rate: the fraction of galaxies with EW_(Hα) >10 A is 59%, compared to 10% among Sloan Digital Sky Survey galaxies of similar masses at z = 0.1. Galaxies with weak Hα emission show absorption lines typical of 2-4 Gyr old stellar populations. The structural parameters of the galaxies, derived from the associated WFC3 F140W imaging data, correlate with the presence of Hα; quiescent galaxies are compact with high Sersic index and high inferred velocity dispersion, whereas star-forming galaxies are typically large two-armed spiral galaxies, with low Sersic index. Some of these star-forming galaxies might be progenitors of the most massive S0 and Sa galaxies. Our results challenge the idea that galaxies at fixed mass form a homogeneous population with small scatter in their properties. Instead, we find that massive galaxies form a highly diverse population at z > 1, in marked contrast to the local universe.

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.

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.

SPATIALLY RESOLVED Hα MAPS AND SIZES OF 57 STRONGLY STAR-FORMING GALAXIES AT z ∼ 1 FROM 3D-HST: EVIDENCE FOR RAPID INSIDE-OUT ASSEMBLY OF DISK GALAXIES

We investigate the buildup of galaxies at z ~ 1 using maps of Hα and stellar continuum emission for a sample of 57 galaxies with rest-frame Hα equivalent widths >100 A in the 3D-HST grism survey. We find that the Hα emission broadly follows the rest-frame R-band light but that it is typically somewhat more extended and clumpy. We quantify the spatial distribution with the half-light radius. The median Hα effective radius re (Hα) is 4.2 ± 0.1 kpc but the sizes span a large range, from compact objects with re (Hα) ~ 1.0 kpc to extended disks with re (Hα) ~ 15 kpc. Comparing Hα sizes to continuum sizes, we find =1.3 ± 0.1 for the full sample. That is, star formation, as traced by Hα, typically occurs out to larger radii than the rest-frame R-band stellar continuum; galaxies are growing their radii and building up from the inside out. This effect appears to be somewhat more pronounced for the largest galaxies. Using the measured Hα sizes, we derive star formation rate surface densities, ΣSFR. We find that ΣSFR ranges from ~0.05 M ☉ yr–1 kpc–2 for the largest galaxies to ~5 M ☉ yr–1 kpc–2 for the smallest galaxies, implying a large range in physical conditions in rapidly star-forming z ~ 1 galaxies. Finally, we infer that all galaxies in the sample have very high gas mass fractions and stellar mass doubling times <500 Myr. Although other explanations are also possible, a straightforward interpretation is that we are simultaneously witnessing the rapid formation of compact bulges and large disks at z ~ 1.

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.

The grism lens-amplified survey from space (Glass). II. Gas-phase metallicity and radial gradients in an interacting system at Z ≃ 2

We present spatially resolved gas-phase metallicity for a system of three galaxies at z=1.85 detected in the Grism Lens-Amplified Survey from Space (GLASS). The combination of HSTs diffraction limit and strong gravitational lensing by the cluster MACS J0717+3745 results in a spatial resolution of ~200-300 pc, enabling good spatial sampling despite the intrinsically small galaxy sizes. The galaxies in this system are separated by 50-200 kpc in projection and are likely in an early stage of interaction, evidenced by relatively high specific star formation rates. Their gas-phase metallicities are consistent with larger samples at similar redshift, star formation rate, and stellar mass. We obtain a precise measurement of the metallicity gradient for one galaxy and find a shallow slope compared to isolated galaxies at high redshift, consistent with a flattening of the gradient due to gravitational interaction. An alternative explanation for the shallow metallicity gradient and elevated star formation rate is rapid recycling of metal-enriched gas, but we find no evidence for enhanced gas-phase metallicities which should result from this effect. Notably, the measured stellar masses log(M/Msun) = 7.2-9.1 probe to an order of magnitude below previous mass-metallicity studies at this redshift. The lowest mass galaxy has properties similar to those expected for Fornax at this redshift, indicating that GLASS is able to directly study the progenitors of local group dwarf galaxies on spatially resolved scales. Larger samples from the full GLASS survey will be ideal for studying the effects of feedback, and the time evolution of metallicity gradients. These initial results demonstrate the utility of HST spectroscopy combined with gravitational lensing for characterizing resolved physical properties of galaxies at high redshift.