Revisiting the Lyman Continuum Escape Crisis: Predictions for z > 6 from Local Galaxies

The intrinsic escape fraction of ionizing Lyman continuum photons ($f_{esc}$) is crucial to understand whether galaxies are capable of reionizing the neutral hydrogen in the early universe at z>6. Unfortunately, it is not possible to access $f_{esc}$ at z>4 with direct observations and the handful of measurements from low redshift galaxies consistently find $f_{esc}$ < 10%, while at least $f_{esc}$ ~ 10% is necessary for galaxies dominate reionization. Here, we present the first empirical prediction of $f_{esc}$ at z>6 by combining the (sparsely populated) relation between [OIII]/[OII] and $f_{esc}$ with the redshift evolution of [OIII]/[OII] as predicted from local high-z analogs selected by their H$\alpha$ equivalent-width. We find $f_{esc}$ = $5.7_{-3.3}^{+8.3}$% at z=6 and $f_{esc}$ = $10.4_{-6.3}^{+15.5}$% at z=9 for galaxies with log(M/M$_{sun}$) ~ 9.0 (errors given as 1$\sigma$). However, there is a negative correlation with stellar mass and we find up to 50% larger $f_{esc}$ per 0.5 dex decrease in stellar mass. The population averaged escape fraction increases according to $f_{esc}$ = $f_{esc,0} ((1+z)/3)^a$, with $f_{esc,0} = 2.3 \pm 0.05$% and $a=1.17 \pm 0.02$ at z > 2 for log(M/M$_{sun}$) ~ 9.0. With our empirical prediction of $f_{esc}$ (thus fixing an important previously unknown variable) and further reasonable assumption on clumping factor and the production efficiency of Lyman continuum photons, we conclude that the average population of galaxies is just capable to reionize the universe by z ~ 6.Comment: 10 pages, 4 figure, 1 table. Accepted by Ap

Sensitive dependence on initial conditions in transition to turbulence in pipe flow

The experiments by Darbyshire and Mullin (J. Fluid Mech. 289, 83 (1995)) on the transition to turbulence in pipe flow show that there is no sharp border between initial conditions that trigger turbulence and those that do not. We here relate this behaviour to the possibility that the transition to turbulence is connected with the formation of a chaotic saddle in the phase space of the system. We quantify a sensitive dependence on initial conditions and find in a statistical analysis that in the transition region the distribution of turbulent lifetimes follows an exponential law. The characteristic mean lifetime of the distribution increases rapidly with Reynolds number and becomes inaccessibly large for Reynolds numbers exceeding about 2200. Suitable experiments to further probe this concept are proposed.Comment: 10 pages, 12 figures; submitted to J. Fluid Mec

The ALPINE-ALMA [C II] survey: Star-formation-driven outflows and circumgalactic enrichment in the early Universe

We study the efficiency of galactic feedback in the early Universe by stacking the [C II] 158 μm emission in a large sample of normal star-forming galaxies at 4   4. From the stacking analysis of the datacubes, we find that the combined [C II] core emission (|v|< 200 km s⁻¹) of the higher-SFR galaxies is extended on physical sizes of ∼30 kpc (diameter scale), well beyond the analogous [C II] core emission of lower-SFR galaxies and the stacked far-infrared continuum. The detection of such extended metal-enriched gas, likely tracing circumgalactic gas enriched by past outflows, corroborates previous similar studies, confirming that baryon cycle and gas exchanges with the circumgalactic medium are at work in normal star-forming galaxies already at early epochs

Provoking Taboos: Representing Holocaust Art Today

Since the mid-1990s, representations of the Holocaust in the visual arts, literature, and popular culture have undergone a paradigm shift, becoming both more transgressive and more scandalous. How and why should artistic and cultural representations of the Holocaust arouse today precisely the kind of emotional provocation that is peculiar to its subject matter? These are the main questions that the artist testimonies and scholarly essays collected by Sophia Komor and Susanne Rohr in The Holocaust, Art, and Taboo: Transatlantic Exchanges on the Ethics and Aesthetics of Representation, invite their readers to grapple with—in utterly engaging and thought-provoking ways

Echoes of Emily

Young Emily Norcross is shy and awkward with few friends. She is the victim of many of her peers’ jokes and constantly doubts herself. Through the encouragement of a teacher, she begins to open up through the writing of poetry. When tragedy strikes, Emily finds comfort and self-confidence through her poetry and the gentle encouragement of the unseen Emily Dickinson

Modeling and fabrication of optically resonant periodic structures

Optically resonant periodic electrode (ORPEL) structures developed for use as an optical modulator at telecommunication wavelengths using standard microelectronic processes have been successfully fabricated. These structures combine passive optical components (i.e. waveguides, diffraction gratings) with optical and/or electrical excitation, which alters the optical properties of the device. Although the electro-optical effect in silicon is weak in comparison to HI-V materials, a change in the free carrier concentration will cause a change in the effective index of refraction, and can alter the resonance wavelength. Optical test results have demonstrated resonance near 1550 nm on devices with grating pitches ranging from 0.68 to 1.08micrometer. Parameters which are important to the electrical operation and optical performance of the devices have been investigated, both experimentally and using computer simulation. Simulation software has proven to be a very useful tool in structural and optical modeling of ORPEL devices; optical modeling predictions and experimental results for 0.70micrometer pitch grating structures are in reasonable agreement. This work will present the theory of operation, device design, fabrication details, and electrical and optical measurements on ORPEL structures

Digested sewage sludge: characterization of a residual and modeling for its disposal in the ocean off Southern California

Sewage sludge is a concentration of the residues that our modern municipal and industrial society discharges to the sewerage system. The sludge solids are removed from the sewage flow by sedimentation and then partially stabilized by biological digestion. Typical digested sludges are 95 to 98 percent water, with the majority of their potential environmental contaminates such as trace metals associated with the two to five percent solids fraction. This particulate matter has usually been characterized only for such gross constituents as total solids, total trace metals, and pesticides. For this work, the sludge particle system was approached on a much more detailed level. There is strong evidence that the particles in digested sludge may cause serious deleterious effects when discharged near the productive surface waters of the ocean. Such effects include disruption of light penetration into the water column. This can drastically reduce photosynthesis, the primary productivity in the ocean. Sludge particles discharged to the ocean are heavier than the surrounding water and tend to settle. They may "blanket" the bottom, interfering with the normal life cycles of bottom-dwelling organisms. The digested sludge, only partially stabilized by treatment processes before discharge, may also drastically alter the chemistry of the sediments where it settles. The very fine material in the sludge does not settle easily and may be carried many kilometers by the prevailing ocean currents. The trace metals and other components incorporated into the particles are also then carried great distances. Since many marine organisms such as bivalves and zooplankton are filter feeders, the presence of sludge-particulate matter of the right size in the water column may lead to uptake of sludge contaminants in the food chain

An alternate approach to measure specific star formation rates at 2<z<7

We trace the specific star formation rate (sSFR) of massive star-forming galaxies ($\gtrsim\!10^{10}\,\mathcal{M}_\odot$) from $z\sim2$ to 7. Our method is substantially different from previous analyses, as it does not rely on direct estimates of star formation rate, but on the differential evolution of the galaxy stellar mass function (SMF). We show the reliability of this approach by means of semi-analytical and hydrodynamical cosmological simulations. We then apply it to real data, using the SMFs derived in the COSMOS and CANDELS fields. We find that the sSFR is proportional to $(1+z)^{1.1\pm0.2}$ at $z>2$, in agreement with other observations but in tension with the steeper evolution predicted by simulations from $z\sim4$ to 2. We investigate the impact of several sources of observational bias, which however cannot account for this discrepancy. Although the SMF of high-redshift galaxies is still affected by significant errors, we show that future large-area surveys will substantially reduce them, making our method an effective tool to probe the massive end of the main sequence of star-forming galaxies.Comment: ApJ accepte