The end of an era:The Population III to Population II transition and the near-infrared background

There are only a few ways to constrain the Era of Reionization and the properties of high redshift (z>6) stars through observations. Here, we discuss one of these observables - the spectrum of the Near Infrared Background - and how it is potentially affected by the transition from Population III to Population II stars. The stronger Lyman-alpha emission expected from massive Population III stars could result in a 'bump' in the spectrum of the Near Infrared Background (referred to in this work as the Lyman-alpha bump). The strength and shape of this bump can reveal properties of Population III stars. The Lyman-alpha bump is predicted to be higher if Population III stars are more massive and present at lower redshifts. The shape of the bump is governed by the star formation rate and the time it takes Population III stars to transition to Population II stars. If Population III stars are indeed massive, a bump is predicted as long as Population III stars exist at z < 15, even if their star formation rate is as low as 10^-7 M_sun yr^-1 Mpc^-3. This means that there may be some observational signature in the Near Infrared Background of small pockets of metal-free gas forming Population III stars at z ~ 6, even if they are quite rare.Comment: 8 pages, 5 figures, accepted to MNRAS. Clarifications were added and typos were fixe

The Cosmic Near Infrared Background: Remnant Light from Early Stars

The redshifted ultraviolet light from early stars at z ~ 10 contributes to the cosmic near infrared background. We present detailed calculations of its spectrum with various assumptions about metallicity and mass spectrum of early stars. We show that if the near infrared background has a stellar origin, metal-free stars are not the only explanation of the excess near infrared background; stars with metals (e.g. Z=1/50 Z_sun) can produce the same amount of background intensity as the metal-free stars. We quantitatively show that the predicted average intensity at 1-2 microns is essentially determined by the efficiency of nuclear burning in stars, which is not very sensitive to metallicity. We predict \nu I_\nu / \dot{\rho}_* ~ 4-8 nW m^-2 sr^-1, where \dot{\rho_*} is the mean star formation rate at z=7-15 (in units of M_sun yr^-1 Mpc^-3) for stars more massive than 5 M_sun. On the other hand, since we have very little knowledge about the form of mass spectrum of early stars, uncertainty in the average intensity due to the mass spectrum could be large. An accurate determination of the near infrared background allows us to probe formation history of early stars, which is difficult to constrain by other means. While the star formation rate at z=7-15 inferred from the current data is significantly higher than the local rate at z<5, it does not rule out the stellar origin of the cosmic near infrared background. In addition, we show that a reasonable initial mass function, coupled with this star formation rate, does not over-produce metals in the universe in most cases, and may produce as little as less than 1 % of the metals observed in the universe today.Comment: 37 pages, 7 figures, (v2) Changes to abstract to emphasize that the excess near infrared background can solely be explained by stars with significant metals. (Metal-free stars are not necessarily needed.) (v3) Expanded discussion on the metallicity constraint. Accepted for publication in Ap

A Novel Approach to Constrain the Escape Fraction and Dust Content at High Redshift Using the Cosmic Infrared Background Fractional Anisotropy

The Cosmic Infrared Background (CIB) provides an opportunity to constrain many properties of the high redshift (z>6) stellar population as a whole. This background, specifically, from 1 to 200 microns, will contain any information about the era of reionization and the stars responsible for producing these ionizing photons. In this paper, we look at the fractional anisotropy delta I/I of this high redshift population, which is the ratio of the magnitude of the fluctuations (delta I) and the mean intensity (I). We show that this can be used to constrain the escape fraction of the population as a whole. The magnitude of the fluctuations of the CIB depend on the escape fraction, while the mean intensity does not. This results in lower values of the escape fraction producing higher values of the fractional anisotropy. This difference is predicted to be larger at the longer wavelengths bands (above 10 microns), albeit it is also much harder to observe in that range. We show that the fractional anisotropy can also be used to separate a dusty from a dust-free population. Finally, we discuss the constraints provided by current observations on the CIB fractional anisotropy.Comment: 8 pages, 4 figures, accepted to ApJ, some clarifications added, matches accepted versio

Mentoring the Mentors: Implementation and Evaluation of Four Fogarty-Sponsored Mentoring Training Workshops in Low-and Middle-Income Countries.

A growing body of evidence highlights the importance of competent mentoring in academic research. We describe the development, implementation, and evaluation of four regional 2-day intensive workshops to train mid- and senior-level investigators conducting public health, clinical, and basic science research across multiple academic institutions in low- and middle-income countries (LMICs) on tools and techniques of effective mentoring. Sponsored by the Fogarty International Center, workshops included didactic presentations, interactive discussions, and small-group problem-based learning and were conducted in Lima, Peru; Mombasa, Kenya; Bangalore, India; and Johannesburg, South Africa, from 2013 to 2016. Mid- or senior-level faculty from multiple academic institutions within each region applied and were selected. Thirty faculty from 12 South America-based institutions, 29 faculty from eight East Africa-based institutions, 37 faculty from 14 South Asia-based institutions, and 36 faculty from 13 Africa-based institutions participated, with diverse representation across disciplines, gender, and academic rank. Discussions and evaluations revealed important comparisons and contrasts in the practice of mentoring, and specific barriers and facilitators to mentoring within each cultural and regional context. Specific regional issues related to hierarchy, the post-colonial legacy, and diversity arose as challenges to mentoring in different parts of the world. Common barriers included a lack of a culture of mentoring, time constraints, lack of formal training, and a lack of recognition for mentoring. These workshops provided valuable training, were among the first of their kind, were well-attended, rated highly, and provided concepts and a structure for the development and strengthening of formal mentoring programs across LMIC institutions

The Cosmic Near Infrared Background II: Fluctuations

The Near Infrared Background (NIRB) is one of a few methods that can be used to observe the redshifted light from early stars at a redshift of six and above. Fluctuations of the NIRB can provide information on the first structures, such as halos and their surrounding ionized regions in the IGM. We combine, for the first time, N-body simulations, radiative transfer code, and analytic calculations of luminosity of early structures to predict the angular power spectrum (C_l) of fluctuations in the NIRB. We study the effects of various assumptions about the stellar mass, the initial mass spectrum of stars, metallicity, the star formation efficiency (f_*), the escape fraction of ionizing photons (f_esc), and the star formation timescale (t_SF), on the amplitude as well as the shape of C_l. The power spectrum of NIRB fluctuations is maximized when f_* is the largest (as C_l ~ (f_*)^2) and f_esc is the smallest. A significant uncertainty in the predicted amplitude of C_l exists due to our lack of knowledge of t_SF of these galaxies, which is equivalent to our lack of knowledge of the mass-to-light ratio. We do not see a turnover in the NIRB angular power spectrum of the halo contribution and explain this as the effect of high levels of non-linear bias. This is partly due to our choice of the minimum mass of halos contributing to NIRB, and a smaller minimum mass, which has a smaller non-linear bias, may still exhibit a turn over. Therefore, both the amplitude and shape of the NIRB power spectrum provide important information regarding the nature of sources contributing to the cosmic reionization. The angular power spectrum of the IGM, in most cases, is much smaller than the halo angular power spectrum. In addition, low levels of the observed mean background intensity tend to rule out high values of f_* > 0.2.Comment: 54 pages, 22 figures, Accepted for publication in ApJ. v2: Comments and references added, along with new figures and a section on fractional anisotrop

Specific Image Characteristics Influence Attitudes about Chimpanzee Conservation and Use as Pets

Chimpanzees are endangered in their native Africa but in the United States, they are housed not only in zoos and research centers but owned privately as pets and performers. In 2008, survey data revealed that the public is less likely to think that chimpanzees are endangered compared to other great apes, and that this is likely the result of media misportrayals in movies, television and advertisements. Here, we use an experimental survey paradigm with composite images of chimpanzees to determine the effects of specific image characteristics. We found that those viewing a photograph of a chimpanzee with a human standing nearby were 35.5% more likely to consider wild populations to be stable/healthy compared to those seeing the exact same picture without a human. Likewise, the presence of a human in the photograph increases the likelihood that they consider chimpanzees as appealing as a pet. We also found that respondents seeing images in which chimpanzees are shown in typically human settings (such as an office space) were more likely to perceive wild populations as being stable and healthy compared to those seeing chimpanzees in other contexts. These findings shed light on the way that media portrayals of chimpanzees influence public attitudes about this important and endangered species

The Cosmic Near Infrared Background. III. Fluctuations, Reionization, And The Effects Of Minimum Mass And Self-Regulation

Current observations suggest that the universe was reionized sometime before z similar to 6. One way to observe this epoch of the universe is through the Near Infrared Background (NIRB), which contains information about galaxies which may be too faint to be observed individually. We calculate the angular power spectrum (C-l) of the NIRB fluctuations caused by the distribution of these galaxies. Assuming a complete subtraction of any post-reionization component, C-l will be dominated by galaxies responsible for completing reionization (e.g., z similar to 6). The shape of C-l at high l is sensitive to the amount of nonlinear bias of dark matter halos hosting galaxies. As the nonlinear bias depends on the mass of these halos, we can use the shape of C-l to infer typical masses of dark matter halos responsible for completing reionization. We extend our previous study by using a higher-resolution N-body simulation, which can resolve halos down to 10(8) M-circle dot. We also include improved radiative transfer, which allows for the suppression of star formation in small-mass halos due to photoionization heating. As the nonlinear bias enhances the dark matter halo power spectrum on small scales, we find that C-l is steeper for the case with a complete suppression of small sources or partial suppression of star formation in small halos (the minimum galaxy mass is M-min = 10(9)M(circle dot) in ionized regions and M-min = 10(8)M(circle dot) in neutral regions) than for the case in which these small halos were unsuppressed. In all cases, we do not see a turnover toward high l in the shape of l(2)C(l).ANR ANR-09-BLAN-0224-02Southeast Physics Network (SEPNet)Science and Technology Facilities Council ST/F002858/1, ST/I000976/1NSF AST-0708176, ST-1009799NASA NNX07AH09G, NNG04G177G, NNX11AE09GNational Science Foundation through TeraGrid resources TG-AST090005Astronom

Green salad intake is associated with improved oral cancer survival and lower soluble CD44 levels

Deficiencies in fruit and vegetable intake have been associated with oral cancer (oral cavity and oropharyngeal). Salivary rinses contain measurable biomarkers including soluble CD44 (solCD44) and total protein, which are known markers of oral cancer risk. This study investigates the effect of nutritional factors on solCD44 and protein levels to evaluate oral cancer risk and survival. We evaluated solCD44 and protein levels from 150 patients with oral and oropharyngeal squamous cell carcinoma and 150 frequency-matched controls. We subsequently characterized the effect of food group consumption and these biomarkers on progression-free survival (PFS) and overall survival (OS). Patients reported eating fewer servings of salad (p = 0.015), while controls reported eating fewer servings of potatoes (p \u3c 0.001). Oral cancer patients who consumed at least one serving per week of green salad were found to have significantly lower CD44 levels than those who ate salad less frequently (mean of log2[solCD44]1.73 versus 2.25, p = 0.014). Patients who consumed at least one serving per week of “salad or other vegetables” had significantly longer PFS (median 43.5 versus 9.1 months, p = 0.003, adjusted hazard ratio (HR) = 0.39 p = 0.014) and OS (median 83.6 versus 10 months, p = 0.008, adjusted HR = 0.04 p = 0.029). These findings suggest that dietary factors, namely greater green salad and vegetable intake, may be associated with lower CD44 levels and better prognosis in oral cancer patients

The Effect of Galactic Properties on the Escape Fraction of Ionizing Photons

The escape fraction, fesc, of ionizing photons from early galaxies is a crucial parameter for determining whether the observed galaxies at z > 6 are able to reionize the high-redshift intergalactic medium. Previous attempts to measure fesc have found a wide range of values, varying from less than 0.01 to nearly 1. Rather than finding a single value of fesc, we clarify through modeling how internal properties of galaxies affect fesc through the density and distribution of neutral hydrogen within the galaxy, along with the rate of ionizing photons production. We find that the escape fraction depends sensitively on the covering factor of clumps, along with the density of the clumped and interclump medium. One must therefore be cautious when dealing with an inhomogeneous medium. Fewer, high-density clumps lead to a greater escape fraction than more numerous low-density clumps. When more ionizing photons are produced in a starburst, fesc increases, as photons escape more readily from the gas layers. Large variations in the predicted escape fraction, caused by differences in the hydrogen distribution, may explain the large observed differences in fesc among galaxies. Values of fesc must also be consistent with the reionization history. High-mass galaxies alone are unable to reionize the universe, because fesc > 1 would be required. Small galaxies are needed to achieve reionization, with greater mean escape fraction in the past.Comment: 27 pages, 8 figures. Accepted to ApJ. v2: Improvements based on referee's comment

Constraining the epoch of reionization with the variance statistic: simulations of the LOFAR case

Several experiments are underway to detect the cosmic redshifted 21-cm signal from neutral hydrogen from the Epoch of Reionization (EoR). Due to their very low signal-to-noise ratio, these observations aim for a statistical detection of the signal by measuring its power spectrum. We investigate the extraction of the variance of the signal as a first step towards detecting and constraining the global history of the EoR. Signal variance is the integral of the signal's power spectrum, and it is expected to be measured with a high significance. We demonstrate this through results from a simulation and parameter estimation pipeline developed for the Low Frequency Array (LOFAR)-EoR experiment. We show that LOFAR should be able to detect the EoR in 600 hours of integration using the variance statistic. Additionally, the redshift ($z_r$) and duration ($\Delta z$) of reionization can be constrained assuming a parametrization. We use an EoR simulation of $z_r = 7.68$ and $\Delta z = 0.43$ to test the pipeline. We are able to detect the simulated signal with a significance of 4 standard deviations and extract the EoR parameters as $z_r = 7.72^{+0.37}_{-0.18}$ and $\Delta z = 0.53^{+0.12}_{-0.23}$ in 600 hours, assuming that systematic errors can be adequately controlled. We further show that the significance of detection and constraints on EoR parameters can be improved by measuring the cross-variance of the signal by cross-correlating consecutive redshift bins.Comment: 13 pages, 14 figures, Accepted for publication in MNRA