Time Delay Measurements for the Cluster-lensed Sextuple Quasar SDSS J2222+2745

We report first results from an ongoing monitoring campaign to measure time delays between the six images of the quasar SDSS\,J2222$+$2745, gravitationally lensed by a galaxy cluster. The time delay between A and B, the two most highly magnified images, is measured to be $\tau_{\rm AB} = 47.7 \pm 6.0$ days (95\% confidence interval), consistent with previous model predictions for this lens system. The strong intrinsic variability of the quasar also allows us to derive a time delay value of $\tau_{\rm CA} = 722 \pm 24$ days between image C and A, in spite of modest overlap between their light curves in the current data set. Image C, which is predicted to lead all the other lensed quasar images, has undergone a sharp, monotonic flux increase of 60-75\% during 2014. A corresponding brightening is firmly predicted to occur in images A and B during 2016. The amplitude of this rise indicates that time delays involving all six known images in this system, including those of the demagnified central images D-F, will be obtainable from further ground-based monitoring of this system during the next few years.Comment: 9 pages, 9 figures, Version accepted for publication in Ap

On the lack of correlation between Mg II 2796, 2803 Angstrom and Lyman alpha emission in lensed star-forming galaxies

We examine the Mg II 2796, 2803 Angstrom, Lyman alpha, and nebular line emission in five bright star-forming galaxies at 1.66<z<1.91 that have been gravitationally lensed by foreground galaxy clusters. All five galaxies show prominent Mg II emission and absorption in a P Cygni profile. We find no correlation between the equivalent widths of Mg II and Lyman alpha emission. The Mg II emission has a broader range of velocities than do the nebular emission line profiles; the Mg II emission is redshifted with respect to systemic by 100 to 200 km/s. When present, Lyman alpha is even more redshifted. The reddest components of Mg II and Lyman alpha emission have tails to 500-600 km/s, implying a strong outflow. The lack of correlation in the Mg II and Lyman alpha equivalent widths, the differing velocity profiles, and the high ratios of Mg II to nebular line fluxes together suggest that the bulk of Mg II emission does not ultimately arise as nebular line emission, but may instead be reprocessed stellar continuum emission.Comment: The Astrophysical Journal, in press. 6 pages, 2 figure

Searching for Cooling Signatures in Strong Lensing Galaxy Clusters: Evidence Against Baryons Shaping the Matter Distribution in Cluster Cores

The process by which the mass density profile of certain galaxy clusters becomes centrally concentrated enough to produce high strong lensing (SL) cross-sections is not well understood. It has been suggested that the baryonic condensation of the intra-cluster medium (ICM) due to cooling may drag dark matter to the cores and thus steepen the profile. In this work, we search for evidence of ongoing ICM cooling in the first large, well-defined sample of strong lensing selected galaxy clusters in the range 0.1 < z < 0.6. Based on known correlations between the ICM cooling rate and both optical emission line luminosity and star formation, we measure, for a sample of 89 strong lensing clusters, the fraction of clusters that have [OII]3727 emission in their brightest cluster galaxy (BCG). We find that the fraction of line-emitting BCGs is constant as a function of redshift for z > 0.2 and shows no statistically significant deviation from the total cluster population. Specific star formation rates, as traced by the strength of the 4000 angstrom break, D_4000, are also consistent with the general cluster population. Finally, we use optical imaging of the SL clusters to measure the angular separation, R_arc, between the arc and the center of mass of each lensing cluster in our sample and test for evidence of changing [OII] emission and D_4000 as a function of R_arc, a proxy observable for SL cross-sections. D_4000 is constant with all values of R_arc, and the [OII] emission fractions show no dependence on R_arc for R_arc > 10" and only very marginal evidence of increased weak [OII] emission for systems with R_arc < 10". These results argue against the ability of baryonic cooling associated with cool core activity in the cores of galaxy clusters to strongly modify the underlying dark matter potential, leading to an increase in strong lensing cross-sections.Comment: 9 Pages, 5 Figures, 1 Tabl

Constraining the metallicities, ages, star formation histories, and ionizing continua of extragalactic massive star populations

We infer the properties of massive star populations using the far-ultraviolet stellar continua of 61 star-forming galaxies: 42 at low-z observed with HST and 19 at z~2 from the Megasaura sample. We fit each stellar continuum with a linear combination of up to 50 single age and single metallicity Starburst99 models. From these fits, we derive light-weighted ages and metallicities, which agree with stellar wind and photospheric spectral features, and infer the spectral shapes and strengths of the ionizing continua. Inferred light-weighted stellar metallicities span 0.05-1.5 Z$_\odot$ and are similar to the measured nebular metallicities. We quantify the ionizing continua using the ratio of the ionizing flux at 900\AA\ to the non-ionizing flux at 1500\AA\ and demonstrate the evolution of this ratio with stellar age and metallicity using theoretical single burst models. These single burst models only match the inferred ionizing continua of half of the sample, while the other half are described by a mixture of stellar ages. Mixed age populations produce stronger and harder ionizing spectra than continuous star formation histories, but, contrary to previous studies that assume constant star formation, have similar stellar and nebular metallicities. Stellar population age and metallicity affect the far-UV continua in different and distinguishable ways; assuming a constant star formation history diminishes the diagnostic power. Finally, we provide simple prescriptions to determine the ionizing photon production efficiency ($\xi_{ion}$) from the stellar population properties. $\xi_{ion}$ has a range of log($\xi_{ion})=24.4-25.7$ Hz erg$^{-1}$ that depends on stellar age, metallicity, star formation history, and contributions from binary star evolution. These stellar population properties must be observationally determined to determine the number of ionizing photons generated by massive stars.Comment: 31 pages, 23 figures, resubmitted to ApJ after incorporating the referee's comments. Comments encourage

Accurately predicting the escape fraction of ionizing photons using restframe ultraviolet absorption lines

The fraction of ionizing photons that escape high-redshift galaxies sensitively determines whether galaxies reionized the early universe. However, this escape fraction cannot be measured from high-redshift galaxies because the opacity of the intergalactic medium is large at high redshifts. Without methods to indirectly measure the escape fraction of high-redshift galaxies, it is unlikely that we will know what reionized the universe. Here, we analyze the far-ultraviolet (UV) H I (Lyman series) and low-ionization metal absorption lines of nine low-redshift, confirmed Lyman continuum emitting galaxies. We use the H I covering fractions, column densities, and dust attenuations measured in a companion paper to predict the escape fraction of ionizing photons. We find good agreement between the predicted and observed Lyman continuum escape fractions (within $1.4\sigma$) using both the H I and ISM absorption lines. The ionizing photons escape through holes in the H I, but we show that dust attenuation reduces the fraction of photons that escape galaxies. This means that the average high-redshift galaxy likely emits more ionizing photons than low-redshift galaxies. Two other indirect methods accurately predict the escape fractions: the Ly$\alpha$ escape fraction and the optical [O III]/[O II] flux ratio. We use these indirect methods to predict the escape fraction of a sample of 21 galaxies with rest-frame UV spectra but without Lyman continuum observations. Many of these galaxies have low escape fractions ($f_{\rm esc} \le 1$\%), but 11 have escape fractions $>1$\%. The methods presented here will measure the escape fractions of high-redshift galaxies, enabling future telescopes to determine whether star-forming galaxies reionized the early universe.Comment: Accepted for publication in A&A. 12 pages, 5 figure

In-situ X-ray Video Microscopy Studies of Al-Si Eutectic Solidification

In-situ studies of Al-Si eutectic growth has been carried out for the first time by X-ray video microscopy during directional solidification of Al-Si-Cu alloys with and without Sr-addtions. The unmodified eutectics showed distinctive non-isothermal growth dynamics, where Si-crystals attained needle-like tip morphologies and progressed under significantly higher undercooling than Al, leading to formation of an irregular eutectic with Si as the leading phase and subsequent nucleation of Al on the Si-surfaces. In the Sr-modified alloys, the eutectic reaction was found to be strongly suppressed, occurring with low nucleation frequencies at undercoolings in the range 10-18 K. In the Cu-enriched melt, the eutectic front was found to attain meso-scale interface perturbations evolving into equiaxed cellular rosettes in order to accommodate to the long-range redistribution of Cu from the composite eutectic interface. The eutectic front also attained short-range microscale interface perturbations consistent with characteristics of a fibrous Si growth, however further improvements in spatial resolution is required in order to study microscale structure formation in greater detail. Evidence was found in support of Si-nucleation occurring on potent particles suspended in the melt. Yet, both with Sr- modified and unmodified alloys, Si precipitation alone was not sufficient to facilitate the eutectic reaction, which apparently required additional undercooling for Al to form on the Si-particles. To what extent nucleation mechanisms in the Cu-enriched systems are transferable to binary or commercial Al-Si alloys remains uncertain

The Mass Distribution of the Strong Lensing Cluster SDSS J1531+3414

We present the mass distribution at the core of SDSS J1531+3414, a strong-lensing cluster at z=0.335. We find that the mass distribution is well described by two cluster-scale halos with a contribution from cluster-member galaxies. New HST observations of SDSS J1531+3414 reveal a signature of ongoing star formation associated with the two central galaxies at the core of the cluster, in the form of a chain of star forming regions at the center of the cluster. Using the lens model presented here, we place upper limits on the contribution of a possible lensed image to the flux at the center region, and rule out that this emission is coming from a background source.Comment: 8 pages, 5 figures; Submitted to Ap

Upscaled modeling of CO2 injection and migration with coupled thermal processes

A practical modeling approach for CO2 storage over relatively large length and time scales is the vertical-equilibrium model, which solves partially integrated conservation equations for flow in two lateral dimensions. We couple heat transfer within the vertical equilibrium framework for fluid flow, focusing on thermal processes that most impact the CO2 plume. We investigate a simplified representation of heat exchange that also includes transport of heat within the plume. In addition, we explore available CO2 thermodynamic models for reliable prediction of density under different injection pressures and temperatures. The model concept is demonstrated on simplified systems.publishedVersio

Gravitational lensing reveals ionizing ultraviolet photons escaping from a distant galaxy

During the epoch of reionisation, neutral gas in the early Universe was ionized by hard ultraviolet radiation emitted by young stars in the first galaxies. To do so, ionizing ultraviolet photons must escape from the host galaxy. We present Hubble Space Telescope observations of the gravitationally lensed galaxy PSZ1-ARC G311.6602-18.4624, revealing bright, multiply-imaged ionizing photon escape from a compact star-forming region through a narrow channel in an optically thick gas. The gravitational lensing magnification shows how ionizing photons escape this galaxy, contributing to the re-ionization of the Universe. The multiple sight lines to the source probe absorption by intergalactic neutral hydrogen on scales of no more than a few hundred, perhaps even less than ten, parsec.Comment: 17 pages, 9 figures. Published in Scienc

The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MEGaSaURA) I: The Sample and the Spectra

We introduce Project MEGaSaURA: The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas. MEGaSaURA comprises medium-resolution, rest-frame ultraviolet spectroscopy of N=15 bright gravitationally lensed galaxies at redshifts of 1.68$<$z$<$3.6, obtained with the MagE spectrograph on the Magellan telescopes. The spectra cover the observed-frame wavelength range $3200 < \lambda_o < 8280$ \AA ; the average spectral resolving power is R=3300. The median spectrum has a signal-to-noise ratio of $SNR=21$ per resolution element at 5000 \AA . As such, the MEGaSaURA spectra have superior signal-to-noise-ratio and wavelength coverage compared to what COS/HST provides for starburst galaxies in the local universe. This paper describes the sample, the observations, and the data reduction. We compare the measured redshifts for the stars, the ionized gas as traced by nebular lines, and the neutral gas as traced by absorption lines; we find the expected bulk outflow of the neutral gas, and no systemic offset between the redshifts measured from nebular lines and the redshifts measured from the stellar continuum. We provide the MEGaSaURA spectra to the astronomical community through a data release.Comment: Resubmitted to AAS Journals. Data release will accompany journal publication. v2 addresses minor comments from refere