The First Galaxies

We review our current understanding of how the first galaxies formed at the end of the cosmic dark ages, a few 100 million years after the Big Bang. Modern large telescopes discovered galaxies at redshifts greater than seven, whereas theoretical studies have just reached the degree of sophistication necessary to make meaningful predictions. A crucial ingredient is the feedback exerted by the first generation of stars, through UV radiation, supernova blast waves, and chemical enrichment. The key goal is to derive the signature of the first galaxies to be observed with upcoming or planned next-generation facilities, such as the James Webb Space Telescope or Atacama Large Millimeter Array. From the observational side, ongoing deep-field searches for very high-redshift galaxies begin to provide us with empirical constraints on the nature of the first galaxies.Comment: 75 pages, 14 figures, draft version for 2011 Annual Reviews of Astronomy and Astrophysic

Radiation Hydrodynamical Instabilities in Cosmological and Galactic Ionization Fronts

Ionization fronts, the sharp radiation fronts behind which H/He ionizing photons from massive stars and galaxies propagate through space, were ubiquitous in the universe from its earliest times. The cosmic dark ages ended with the formation of the first primeval stars and galaxies a few hundred Myr after the Big Bang. Numerical simulations suggest that stars in this era were very massive, 25 - 500 solar masses, with H II regions of up to 30,000 light-years in diameter. We present three-dimensional radiation hydrodynamical calculations that reveal that the I-fronts of the first stars and galaxies were prone to violent instabilities, enhancing the escape of UV photons into the early intergalactic medium (IGM) and forming clumpy media in which supernovae later exploded. The enrichment of such clumps with metals by the first supernovae may have led to the prompt formation of a second generation of low-mass stars, profoundly transforming the nature of the first protogalaxies. Cosmological radiation hydrodynamics is unique because ionizing photons coupled strongly to both gas flows and primordial chemistry at early epochs, introducing a hierarchy of disparate characteristic timescales whose relative magnitudes can vary greatly throughout a given calculation. We describe the adaptive multistep integration scheme we have developed for the self-consistent transport of both cosmological and galactic ionization fronts.Comment: 6 pages, 4 figures, accepted for proceedings of HEDLA2010, Caltech, March 15 - 18, 201

The faintest galaxies

We investigate the nature of Ultra Faint dwarf spheroidal galaxies (UF dSphs) in a general cosmological context, simultaneously accounting for various "classical" dSphs and Milky Way (MW) properties, including their Metallicity Distribution Function (MDF). The model successfully reproduces both the observed [Fe/H]-Luminosity relation and the mean MDF of UFs. According to our results UFs are the living fossils of H2-cooling minihaloes formed at z>8.5, i.e. before the end of reionization. They are the oldest and the most dark matter-dominated (M/L > 100) dSphs in the MW system, with a total mass of M = 10^(7-8) Msun. The model allows to interpret the different shape of UFs and classical dSphs MDF, along with the frequency of extremely metal-poor stars in these objects. We discuss the "missing satellites problem" by comparing the UF star formation efficiencies with those derived for minihaloes in the Via Lactea simulation.Comment: To appear in the conference proceeding: "First Stars and Galaxies: Challenges in the Next Decade" . Publisher: American Institute of Physics. Editors: V. Bromm, D. Whalen, N. Yoshid

MANGANESE LIMITATION AS A MECHANISM FOR REDUCED DECOMPOSITION IN SOILS UNDER LONG-TERM ATMOSPHERIC NITROGEN DEPOSITION

Long-term atmospheric nitrogen (N) deposition has been shown to reduce leaf litter and lignin decomposition in forest soils, leading to an accumulation of soil carbon. Reduced decomposition has been accompanied by altered structure and function of fungal communities, the primary decomposers in forest ecosystems; however, a mechanistic understanding of fungal responses to chronic N enrichment is lacking. A reduction in soil and litter manganese (Mn) concentrations under N enrichment (i.e., Mn limitation) may explain these observations, because Mn is a cofactor and regulator of lignin-decay enzymes produced by fungi. We conducted a 6-month incubation study to evaluate the effect of Mn availability on decomposition dynamics in chronically N-enriched soils. We measured ligninolytic enzyme activities, mass loss and lignin (% change) in litter, and characterized the whole litter fungal community by ITS2 metabarcoding. We show a significant positive correlation between Mn availability and ligninolytic enzyme activities in litter. In addition, we demonstrate an increase in the relative abundance of ‘weak’ decomposers (e.g., yeasts) under long-term N enrichment, and a reversal of this response with Mn amendment. Our results suggest that higher Mn availability may promote fungal communities better adapted to decompose lignin. We conclude that Mn limitation plays an important role in decomposition dynamics under long-term atmospheric N deposition and may represent a mechanism that explains reduced decomposition and soil C accumulation under this global change factor

Interactions between eagles and humans in the James River Bald Eagle Concentration Area

The lower James River supports the largest known concentration of summering eagles in eastern North America. In recent years, both the number of eagles using the river and their distribution along the shoreline appear to have increased substantially. At the same time, an increase in the human population surrounding the lower river has lead to an increase in the use of the river for recreational activities. These trends have heightened concerns within the management community about potential interactions and conflicts between these two user populations. In the summer of 1997, an investigation was initiated to collect data for the purpose of: 1) redefining the boundaries of the James River Bald Eagle concentration area, 2) determining the current level of human use within a section of the lower James River, and 3) investigating potential interactions between the human and eagle populations during the summer months. These objectives were accomplished using a combination of an extended shoreline survey and intensive observations of humans and eagles within the heart of the historic concentration area. The James River Bald Eagle concentration area has expanded well beyond the historic survey area. Elevated numbers of eagles now extend from Jones Neck down river to Fort Eustis, a distance of 140 river kilometers that contains 235 km of primary shoreline. The peak count of 448 eagles on 11 June approaches an average of 2 birds/krn of shoreline for the entire study area. In addition to the expansion of eagles along the shoreline, an increase in both the number and distribution of sites used for nocturnal roosts was documented. Four new communal roost sites spanning the length of the study area were located

Negative emotional reactivity as a marker of vulnerability in the development of borderline personality disorder symptoms

Negative emotionality is a distinguishing feature of borderline personality disorder (BPD). However, this person-level characteristic has not been examined as a marker of vulnerability in the development of this disorder. The current study utilized a multi-method approach to examine the interplay between negative emotional reactivity and cumulative exposure to family adversity on the development of BPD symptoms across three years (ages 16–18) in a diverse, at-risk sample of adolescent girls (N=113). A latent variable of negative emotional reactivity was created from multiple assessments at age 16: (1) self-report, (2) emotion ratings to stressors from ecological assessments across one week, and (3) observer-rated negative affectivity during a mother-daughter conflict discussion task. Exposure to family adversity was measured cumulatively between ages 5 and 16 from annual assessments of family poverty, single parent household, and difficult life circumstances. Results from latent growth curve models demonstrated a significant interaction between negative emotional reactivity and family adversity, such that exposure to adversity strengthened the association between negative emotional reactivity and BPD symptoms. Additionally, family adversity predicted increasing BPD symptoms during late adolescence. These findings highlight negative emotional reactivity as a marker of vulnerability that ultimately increases risk for the development of BPD symptoms

Detectability of the First Cosmic Explosions

We present a fully self-consistent simulation of a synthetic survey of the furthermost cosmic explosions. The appearance of the first generation of stars (Population III) in the Universe represents a critical point during cosmic evolution, signaling the end of the dark ages, a period of absence of light sources. Despite their importance, there is no confirmed detection of Population III stars so far. A fraction of these primordial stars are expected to die as pair-instability supernovae (PISNe), and should be bright enough to be observed up to a few hundred million years after the big bang. While the quest for Population III stars continues, detailed theoretical models and computer simulations serve as a testbed for their observability. With the upcoming near-infrared missions, estimates of the feasibility of detecting PISNe are not only timely but imperative. To address this problem, we combine state-of-the-art cosmological and radiative simulations into a complete and self-consistent framework, which includes detailed features of the observational process. We show that a dedicated observational strategy using $\lesssim 8$ per cent of total allocation time of the James Webb Space Telescope mission can provide us up to $\sim 9-15$ detectable PISNe per year.Comment: 9 pages, 8 figures. Minor corrections added to match published versio