Metallicity Floor Research Articles

THE BIRTH OF A GALAXY: PRIMORDIAL METAL ENRICHMENT AND STELLAR POPULATIONS

By definition, Population III stars are metal-free, and their protostellar collapse is driven by molecular hydrogen cooling in the gas-phase, leading to large characteristic masses. Population II stars with lower characteristic masses form when the star-forming gas reaches a critical metallicity of 10^{-6} - 10^{-3.5} Z_\odot. We present an adaptive mesh refinement radiation hydrodynamics simulation that follows the transition from Population III to II star formation. The maximum spatial resolution of 1 comoving parsec allows for individual molecular clouds to be well-resolved and their stellar associations to be studied in detail. We model stellar radiative feedback with adaptive ray tracing. A top-heavy initial mass function for the Population III stars is considered, resulting in a plausible distribution of pair-instability supernovae and associated metal enrichment. We find that the gas fraction recovers from 5 percent to nearly the cosmic fraction in halos with merger histories rich in halos above 10^7 solar masses. A single pair-instability supernova is sufficient to enrich the host halo to a metallicity floor of 10^{-3} Z_\odot and to transition to Population II star formation. This provides a natural explanation for the observed floor on damped Lyman alpha (DLA) systems metallicities reported in the literature, which is of this order. We find that stellar metallicities do not necessarily trace stellar ages, as mergers of halos with established stellar populations can create superpositions of t-Z evolutionary tracks. A bimodal metallicity distribution is created after a starburst occurs when the halo can cool efficiently through atomic line cooling.

Morning Cloud, Evening Rain

Morning Cloud, Evening Rain Wang Ping (bio) A dream is not a dream A butterfly not a butterfly In the cloud, a pining spirit A myth in the dream’s red chamber It’s dawn. Our cruise ship has passed the roaring Qutang Gorge and entered Wushan on the Yangtze. The deck is finally empty after an all-night party of drinking and gambling. I sneak past the sleeping guard to do yoga on the area reserved for the first-class passengers. When I look up from a back bend, she appears before me like an apparition, her slender waist and full hips shimmering through a silk gown, her painted toes curving through golden slippers, blond curls hugging her breasts. Her beauty takes my breath away, though I am supposed to detest her—a woman dressed to give pleasure to anyone who can pay. Yet she pulls me like the moon. The melancholy between her eyebrows makes my heart throb with pain. Below the deck, the tour guide is knocking on the first-class cabins, her shrill voice cutting through the metal floor. “Get up. We’re reaching Wushan Goddess Peak. Your tour counts for nothing unless you see the goddess.” When no one stirs, she shouts, “I’ve done my job. Don’t regret it later. Don’t ask for a refund.” I smile as I listen to the commotion downstairs. She knows how to move people. Money is the engine that drives China forward. Thick clouds hang on the mountains, shrouding the river, the boat, and the girl in white silk. How did she get here? Since I boarded this three-star [End Page 48] boat yesterday afternoon, I have combed though the first-, second-, and third-class passengers who live along the Three Gorges, or used to, before they were removed for the dam construction. I should have known better: why would any locals squander their money touring their homeland? The girl couldn’t have boarded the ship with us. I’d have spotted her right away. Light peeks out of the clouds, casting her shadow on the river. Even her shadow is beautiful and forlorn. It points north to a steep mountaintop, where mist hugs the shoulders of a slender rock. Is that the Wushan goddess the guide has been bragging about, the crown jewel of our three-day tour? Everything else pales after her, she told Dan. I was struck by the enthusiasm in her gleaming eyes. She’s a shrewd businesswoman. What’s her interest in a rock that doesn’t have much commercial value except that it provides her with a job? We disliked each other the minute we met. I detest her heavy makeup and elaborate hairdo, her tight T-shirt and jeans that show every inch of her robust curves, her shrill voice and the purple bags under the bulging eyes revealing her oversexed lifestyle. Likewise, she seems to hate everything about me: my blunt questions, my casual traveler’s clothes, my fluent English and my American colleague. The minute we boarded, she pulled Dan to her side, announcing in her broken English that it was her duty to give him, the only foreigner on board, her personal attention. Dan laughed when I translated her words into comprehensible English. She glared at me with her watery eyes: Just watch how I snatch the meat right out of your wrinkled mouth, you arrogant hag! “There she is, everyone, our goddess, our Chinese Venus!” the guide shrieks through a megaphone. The deck is packed. Dan stands next to her, craning his neck to locate the peak. She takes his hand and points it to the north shore. “There, the slenderest one. Doesn’t it look like a girl facing clouds? Isn’t she beautiful?” There seems to be someone in the folds of the mountain With eyes that hold laughter and pearls of smile. She starts singing “Shangui” from Qu Yuan’s Nine Songs, a ritual performance for gods and kings from two thousand years ago. Shangui is a goddess who roams the Three Gorges, gathering herbs as she waits for her [End Page 49] wandering warrior—“her wandering warrior—the God of...

Technical Note: Estimating Goat and Sheep Manure Production and their Nutrient Contribution in the Chesapeake Bay Watershed

The objectives of this study were to estimate the: (1) the daily manure (feces + urine) outputs by goats and sheep and characterize the nutrient composition, and (2) potential contribution of goats and sheep to the nutrients in the Chesapeake Bay Watershed (Bay) watershed. Manure (feces+ urine) was collected from four 8-month-old mixed-breed hair sheep rams and four 14-month-old meat goat bucks housed in aluminum metabolism crates with rubber-coated expanded metal floors. The animals were fitted with fecal collection bags. Animals were fed a diet of chopped grass hay (75%) and corn/soybean meal concentrates (25%). The animals' numbers in the Chesapeake Bay watershed were obtained from USDA national agricultural animal census database. The manure nutrients excreted by the goats and sheep were compared to those of dairy cows in the watershed to get a feel for the relative impacts. The nitrogen (N), phosphorus (P), and potassium (K) ratios were 8.8:1:6.5 and 8.3:1:6.9, in goat and sheep manure respectively, and over 50% of N and K were in the urine. The goat population in the Bay watershed increased by over 200% between 1997 and 2007, while the sheep population declined by about 10% over the same period of time. Based on the animal census for 2007 in the Bay watershed, the combined N and P excreted by goats and sheep combined were less than 3% of the nutrients excreted by dairy cows.

DEEP SPECTROSCOPY OF ULTRA-STRONG EMISSION-LINE GALAXIES

Ultra-strong emission-line galaxies (USELs) with extremely high equivalent widths (EW(Hβ) ≳ 30 Å) can be used to pick out galaxies of extremely low metallicity in the z = 0–1 redshift range. Large numbers of these objects are easily detected in deep narrow band searches. Since most have detectable [O iii]λ4363, their metallicities can be determined using the direct method. These large samples hold out the possibility for determining whether there is a metallicity floor for the galaxy population. In this, the second of our papers on the topic, we describe the results of an extensive spectroscopic follow-up of the Kakazu et al. catalog of 542 USELs carried out with the DEIMOS spectrograph on Keck. We have obtained high S/N spectra of 348 galaxies. The two lowest metallicity galaxies in our sample have 12 + log(O/H) = 6.97 ± 0.17 and 7.25 ± 0.03—values comparable to the lowest metallicity galaxies found to date. We determine an empirical relation between metallicity and the R23 parameter for our sample, and we compare this to the relationship for low-redshift galaxies. The determined metallicity–luminosity relation for this sample is compared with that of magnitude selected samples in the same redshift range. The emission-line-selected galaxies show a metal–luminosity relation where the metallicity decreases with luminosity, and they appear to define the lower bound of the galaxy metallicity distribution at a given continuum luminosity. We also compute the Hα luminosity function of the USELs as a function of redshift and use this to compute an upper bound on the Lyα emitter luminosity function over the z = 0–1 redshift range.

Mitologiziranoto gumno vo slovenskata tradicionalna kultura - II<br>The Mythologized Threshing Floor in the Slavic Traditional Culture - II</br>

In this part special place is given to the “Myth of the Metallic (Copper / Bronze) Threshing Floor”, present in the toponyms, legends, magical stories and in the mediaeval apocryphal texts. It contains analyses of the next mythical elements: the metallic components (threshing floor, castle, field, plants, food …); the connection between the mythical threshing floor and the cosmological myths about the first mountain; the relation between the “metallic threshing floor” and the “metallic shrine”. The similarity between the threshing floor and one type of the Slavic pagan shrines with circular form, and the representation of the threshing floor on the ritual loaves from the 19th century are also discussed. Elaboration is given to the chthonic and “outer world” location of the metallic threshing floor, and the basic actions that take place on it: the fight between the hero and the dragon; the holy marriage between the hero (=sky / cosmic axis) and the Earth, (=ground upon which the threshing floor lies).

Discharge Properties of Hippocampal Neurons during Performance of a Jump Avoidance Task

We recorded single hippocampal cells while rats performed a jump avoidance task. In this task, a rat was dropped onto the metal floor of a 33 cm gray wooden cube and was given a mild electric shock if it did not jump up onto the box rim in <15 s. We found that many hippocampal pyramidal cells and most interneurons discharged preferentially at the drop, the jump, or on both events. By simultaneously recording the hippocampal EEG, we found that the discharge of most of the event-related pyramidal cells was modulated by the theta rhythm and moreover that discharge precessed with theta cycles in the same manner seen for pyramidal cells in their role as place cells. The elevations of firing rate at drop and jump were accompanied by increases in theta frequency. We conclude that many of the features of event-related discharge can be interpreted as being equivalent to the activity of place cells with firing fields above the box floor. Nevertheless, there are sufficient differences between expectations from place cells and observed activity to indicate that pyramidal cells may be able to signal events as well as location.

Are double bunks used by indoor wintering sheep?: Testing a proposal for organic farming in Norway

The frequency with which ewe lambs lay on wooden surfaces at two levels, called “double bunks,” was documented by video recording at 6, 11 and 18 months of age: the number in each of 4 pens ( n = 4) lying either on double bunks (DBs) or on the expanded metal floor (EMF) was recorded. At 6 months, lambs were sheared half way through the research period and DBs of two different heights (50/60 cm) and depths (60/75 cm) were tested. At other ages the lambs were sheared before testing and all DBs were the 60 cm × 60 cm design. Fully fleeced lambs aged 6 months preferred to lie on EMF rather than DB ( P < 0.001). After shearing, the use of EMF for resting declined ( P < 0.05) and no significant preference between EMF and DB was found. The lambs tended to lie less when newly sheared ( P = 0.06). At 11 months, sheared lambs used DB just as much as EMF, whereas 18 month old sheared ewe lambs tended to choose DB to lie on ( P = 0.09). At 6 months, there was a tendency for more lambs to rest at ground level in the DB when headroom was higher at 60 cm ( P = 0.1). No other preferences between DB designs were found. The results are discussed according to the regulations for organic sheep farming in Norway. The lambs showed little preference for resting on a DB compared to EMF, so there is insufficient evidence to recommend a two-level, wooden lying area for sheep.

Chemical evolution of the Galaxy disk in connection with large-scale winds

AbstractComparison of elemental abundance features between old and young thin disk stars may reveal the action of ravaging winds from the Galactic bulge, which once enriched the whole disk, and set up the steep abundance gradient in the inner disk (RGC ≲ 10–;12 kpc) and simultaneously the metallicity floor ([Fe/H]~ −0.5) in the outer disk. After the end of a crucial influence by winds, chemical enrichment through accretion of a metal-poor material from the halo onto the disk gradually reduced the metallicity of the inner region, whereas an increase in the metallicity proceeded beyond a solar circle. This results in a flattening of abundance gradient in the inner disk, and our chemical evolution models confirm this mechanism for a flattening, which is in good agreement with the observations. Our scenario also naturally explains an observed break in the metallicity floor of the outer disk by young stars since the limit of self-enrichment in the outer disk is supposed to be [Fe/H]≲ −1 and inevitably incurs a direct influence of the dilution by a low-metal infall whose metallicity is [Fe/H]~ −1. Accordingly, we propose that the enrichment by large-scale winds is a crucial factor for chemical evolution of the disk, and claim to reconsider the models thus far for the disk including the solar neighborhood, in which the metallicity is predicted to monotonously increase with time. Furthermore, we anticipate that a flattening of abundance gradient together with a metal-rich floor in the outer disk are the hallmark of disk galaxies with significant central bulges.

Constrained semi-analytical models of galactic outflows

We present semi-analytic models of galactic outflows that are constrained by available observations on high-redshift star formation and reionization. Galactic outflows are modelled in a manner akin to models of stellar wind-blown bubbles. Large-scale outflows can generically escape from low-mass haloes (M≲ 109M⊙) for a wide range of model parameters while this is not the case in high-mass haloes (M≳ 1011M⊙). The flow generically accelerates within the halo virial radius, then starts to decelerate, and traverses well into the intergalactic medium (IGM), before freezing to the Hubble flow. The acceleration phase can result in shell fragmentation due to the Rayleigh–Taylor instability, although the final outflow radius is not significantly altered. The gas-phase metallicities of the outflow and within the galaxy are computed assuming uniform instantaneous mixing. Ionization states of different metal species are calculated and used to examine the detectability of metal lines from the outflows. The global influence of galactic outflows is also investigated using porosity-weighted averages and probability density functions of various physical quantities. Models with only atomic cooled haloes significantly fill the IGM at z∼ 3 with metals (with −2.5 ≳[Z/Z⊙]≳−3.7), the actual extent depending on the efficiency of winds, the initial mass function and the fractional mass that goes through star formation. The reionization history has a significant effect on the volume filling factor, due to radiative feedback. In these models, a large fraction of outflows at z∼ 3 are supersonic, hot (T≥ 105K) and have low density, making metal lines difficult to detect. They may also result in significant perturbations in the IGM gas on scales probed by the Lyman α forest. On the contrary, models including molecular cooled haloes with a normal mode of star formation can potentially volume fill the universe at z≥ 8 without drastic dynamic effects on the IGM, thereby setting up a possible metallicity floor (−4.0 ≤[Z/Z⊙]≤−3.6). The fluctuations of order unity at z∼ 8 that become the mildly non-linear fluctuations traced by Lyman α forest at z < 4 will then have this metallicity. Interestingly, molecular cooled haloes with a ‘top-heavy’ mode of star formation are not very successful in establishing the metallicity floor because of the additional radiative feedback that they induce.

The Metallicity of Intergalactic Gas in Cosmic Voids

We have used the Hubble/STIS and FUSE archives of ultraviolet spectra of bright AGN to identify intergalactic Lya absorbers in nearby (z < 0.1) voids. From a parent sample of 651 Lya absorbers, we identified 61 void absorbers located more than 1.4/h_70 Mpc from the nearest L* or brighter galaxy. Searching for metal absorption in high-quality (S/N > 10) spectra at the location of three diagnostic metal lines (O VI 1032, C IV 1548, Si III 1206), we detected no metal lines in any individual absorber, or in any group of absorbers using pixel co-addition techniques. The best limits on metal-line absorption in voids were set using four strong Lya absorbers with N(H I) > 10^{14} cm^-2, with 3-sigma equivalent-width limits ranging from 8 mA (O VI), 7-15 mA (C IV), and 4-10 mA (Si III). Photoionization modeling yields metallicity limits Z < 10^{-1.8+/-0.4} Z_sun, from non-detections of C IV and O VI, some 6 times lower than those seen in Lya and OVI absorbers at z < 0.1. Although the void Lya absorbers could be pristine material, considerably deeper spectra are required to rule out a universal metallicity floor produced by bursts of early star formation, with no subsequent star formation in the voids. The most consistent conclusion derived from these low-z results, and similar searches at z = 3-5, is that galaxy filaments have increased their mean IGM metallicity by factors of 30-100 since z = 3.

High‐Redshift Intergalactic CivAbundance Measurements from the Near‐Infrared Spectra of Twoz∼ 6 QSOs

New measurements of the z ~ 6 intergalactic C IV abundance are presented, using moderate-resolution IR spectra of two QSOs taken with GNIRS on Gemini-South. These data were systematically searched for high-redshift C IV absorption lines, using objective selection criteria. Comprehensive tests were performed to quantify sample incompleteness, as well as the rate of false-positive C IV identifications. The trend of constant Ω(z) observed at z ~ 2-5 appears to continue to z ~ 6, the highest observed redshift. The C IV sample is also consistent with the redshift-invariant form of the C IV column density distribution reported by Songaila at lower redshift, although with fairly large uncertainties due to a smaller sample size and noisier infrared data. The constant value of Ω does not necessarily imply that the IGM was infused with an early metallicity floor, but the presence of early C IV does indicate that heavy-element enrichment began 1 Gyr after the big bang. The lack of a decline in Ω at high redshift may indicate that integrated C IV measurements are sensitive to the instantaneous rate of feedback from galaxy formation at each epoch. Alternatively, it could result from a balance in the evolution of the intergalactic gas density, ionization conditions, and heavy-element abundance over time.

Assessment of the Non All-in All-out System and the All-in All-out System for Sows and Their Suckling Piglets

The goal of this study was to investigate the behavior of sows and their piglets reared using the non-all-in all-out system and the all-in all-out system during a 3-week lactation period. The 24 LandracexYorkshire sows (range of parity: 2 to 4) and their litters (range of litter size: 8 to 13 piglets) for each treatment (8 sows/replication) were used in this experiment. The sows were housed in farrowing crates (0.6x2.1 m) located in pens (2.4x1.8 m) with totally perforated metal flooring. The crates were kept in an experimental room that was thermostatically controlled to approximately 23°C. A 250-W infrared heat lamp was turned on above the creep area during lactation. The sows and piglets were conventionally managed. The animals were recorded during a 24-h period at 1, 4, 7, 14 and 21 days postpartum. The videotapes were scanned every minute to obtain an instantaneous behavioral sample. In the behaviors of sows, lateral recumbency decreased and ventral recumbency increased from 1 day postpartum to 21 days postpartum. In comparison to the AIAOS, sows in the NAIAOS spent much less time on lateral recumbency (p<0.01), whereas they spent much more time on ventral recumbency and sitting at 4 days postpartum (p<0.05 and p<0.05). In the behaviors of piglets, lying increased and unsuccessful suckling decreased until 21 days postpartum. Compared to the AIAOS at 4 days postpartum, piglets in the NAIAOS spent less time lying (p<0.01), whereas they spent much more time walking and unsuccessful suckling (p<0.01 and p<0.05). These results suggest that the all-in all-out system may be preferable to the non-all-in all-out system for promoting welfare.

Preferences of sheep for different types of pen flooring

In countries where the climate makes it practical with indoor housing during cold periods of the year and access to straw is limited, e.g. Iceland and Norway, housing of sheep on slats or expanded metal floors is common practice. However, European regulations for organic farming require that all animals should have access to a lying area with solid floor. The objective of this experiment was to investigate sheep preferences for different types of pen flooring. In Experiment 1, a total number of 16 ewes, divided into four groups, were subjected to four different treatments. In each treatment, the ewes could choose between two lying areas with one of the following flooring materials: (1) solid wood versus rubber mats, (2) expanded metal versus solid wood, (3) solid wood versus straw, (4) expanded metal versus straw. In Experiment 2, a total number of eight ewes were individually subjected to the same treatments, first fully coated and then sheared. The ewes were video taped for 48 h in each treatment period. In Experiment 1, the first animal that lay down after feeding preferred to lie down on straw or wood to expanded metal and straw to wooden floor ( P < 0.05), but this first choice did not reflect the overall flooring preference for unsheared ewes. The groups of unsheared ewes showed no significant preferences for lying area. In Experiment 2, single housed, unsheared ewes preferred wooden floor to rubber mats ( P < 0.05), and tended to prefer expanded metal floor to straw ( P = 0.08). There were no significant preferences in the two other treatments. After shearing, the ewes’ preferred wooden floor to expanded metal ( P < 0.05), straw to wooden floor ( P < 0.05), and straw to expanded metal floor ( P< 0.0001). There were no significant preferences between rubber mats and wooden floor. Mean lying time (% of observations) for all treatments was 64.7% for unsheared ewes, and there were no significant differences between treatments. Mean lying time (% of observations) for all treatments the first 2–3 days after shearing was 43%. Significant differences in pre-shearing versus post-shearing lying times (% of observations) existed when the ewes were housed in pens with no straw ( P < 0.05), this was not the case when the ewes had access to straw. In conclusion, sheared but not unsheared ewes, preferred softer floors with low thermal conductivity (straw and wood). The less dramatically reduction in lying time (% of observations) after shearing when the ewes had access to straw, suggest that access to straw the first weeks after shearing may improve animal welfare.

Effect of floor type and dietary molybdenum content on the liver copper concentration at slaughter and performance of intensively finished lambs

A 3×2 factorial experiment was used to evaluate the effects of added molybdenum (Mo) at the rate of 0, 4 or 8 ppm in the diet and two floor types (straw bedding or galvanised expanded metal) on 92 Texel cross intensively fed lambs in relation to hepatic copper levels and lamb growth. The lambs had ad libitum access to a coarse commercial lamb concentrate. The mean crude protein (%), copper (Cu) concentration (mg/kg) and background Mo (mg/kg) of the diets as fed were 18.6, 9.7 and 0.92, respectively. The lambs were slaughtered when they reached 38 kg live weight. Following slaughter, the caudate lobe of the liver was removed for Cu analysis. There was no effect ( P>0.05) of Mo level or floor type on lamb growth rate (mean 411±7.2 g/hd/day) or kill-out proportion. The added Mo was more effective in lowering liver copper values when the lambs were housed on straw bedding especially at the 4 ppm inclusion level. For the 4 and 8 ppm Mo inclusion, the respective reduction in liver copper values was 21% ( P<0.05) and 43% ( P<0.001) when lambs were housed on expanded metal flooring and 52% ( P<0.001) and 62% ( P<0.001) when lambs were bedded on straw. There was an interaction between floor type and the level of molybdenum inclusion. Overall, when lambs were bedded with straw, the hepatic Cu liver value was 15% lower than on the expanded metal, while if the 0 level Mo inclusion treatments are excluded, the effect of the straw was to lower the liver copper value by 32%. At the 4 ppm Mo inclusion, there was a positive relationship between liver weight and liver Cu concentration, although the liver Cu concentration did not approach what might be considered potentially toxic values. In conclusion, high Mo inclusion did not affect lamb growth rate and there were significant differences in its effect on hepatic copper levels depending on inclusion level and floor type. For intensively fed lambs, liver Cu accumulation and risk from Cu toxicity may be reduced, without loss of performance, by housing lambs on straw bedding when Mo is added to the diet and it is also possible that the Zn coating, frequently applied to protect metal flooring, may also confer protective properties evidenced in the absence of Mo. These outcomes should be taken into account when designing strategies for minimising copper toxicity in intensively fed lambs.

The Distribution of Metallicity in the Intergalactic Medium atz ∼ 2.5: Oviand CivAbsorption in the Spectra of Seven QSOs

We present a direct measurement of the metallicity distribution function for the high-redshift intergalactic medium (IGM). We determine the shape of this function using survival statistics, which incorporate both detections and nondetections of O VI and C IV absorption, associated with H I lines in high-resolution quasar spectra. The O VI sample (taken from seven QSOs at zabs ~ 2.5) contains lines with N ≥ 1013.6, encompassing ~50% of all baryons at z ~ 2.5. Our survey accounts for ≈98.8% of the C IV mass and ≈90% of the O VI mass in the universe at this epoch. We find a median intergalactic abundance of [O,C/H] = -2.82; the differential abundance distribution is approximately lognormal with mean ≈ -2.85 and σ = 0.75 dex. We discuss the sensitivity of these results to the assumed form of the ionizing UV radiation field. Some ~60%-70% of lines in the Lyα forest are enriched to observable levels of [O,C/H] -3.5, while the remaining ~30% of the lines have even lower abundances. Thus we have not detected a universal metallicity floor, as has been suggested for some Population III enrichment scenarios. In fact, we argue that the bulk of the intergalactic metals formed later than the first stars that are thought to have triggered reionization. We do not observe a strong trend of decreasing metallicity toward the lower density IGM, at least within regions that would be characterized as filaments in numerical simulations. However, an [O/H] enhancement may be present at somewhat high densities. We estimate that roughly half of all baryons at these redshifts have been enriched to [O,C/H] -3.5. Using a simple closed box model for the metallicity evolution of the IGM, we estimate the chemical yield of galaxies formed prior to z ~ 2.5, finding that the typical galaxy recycled 0.1%-0.4% of its mass back into the IGM as heavy elements in the first 3 Gyr after the big bang.

The Era of Massive Population III Stars: Cosmological Implications and Self‐Termination

The birth and death of the first generation of stars have important implications for the thermal state and chemical properties of the intergalactic medium (IGM) in the early universe. Sometime after recombination, the neutral chemically pristine gas was reionized by ultraviolet photons emitted from the first stars but was also enriched with heavy elements when these stars ended their lives as energetic supernovae. Using the results from previous high-resolution cosmological simulations of early structure formation that include radiative transfer, we show that a significant volume fraction of the IGM can be metal polluted, as well as ionized, by massive Population III stars formed in small-mass (~106-107 M?) halos early on. If most of the early generation stars die as pair-instability supernovae with energies up to ~1053 ergs, the volume-averaged mean metallicity will quickly reach Z ~ 10-4 Z? by a redshift of ~15-20, possibly causing a transition to the formation of a stellar population that is dominated by low-mass stars. In this scenario, the early chemical enrichment history should closely trace the reionization history of the IGM, and the end of the Population III era is marked by the completion of reionization and preenrichment by z ~ 15. We conclude that, while the preenrichment may partially account for the metallicity floor in high-redshift Ly? clouds, it does not significantly affect the elemental abundance in the intracluster medium.

Intergalactic HiiRegions Discovered in SINGG

A number of very small isolated HII regions have been discovered at projected distances up to 30 kpc from their nearest galaxy. These HII regions appear as tiny emission line objects in narrow band images obtained by the NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG). We present spectroscopic confirmation of four isolated HII regions in two systems, both systems have tidal HI features. The results are consistent with stars forming in interactive debris due to cloud-cloud collisions. The H-alpha luminosities of the isolated HII regions are equivalent to the ionizing flux of only a few O stars each. They are most likely ionized by stars formed in situ, and represent atypical star formation in the low density environment of the outer parts of galaxies. A small but finite intergalactic star formation rate will enrich and ionize the surrounding medium. In one system, NGC 1533, we calculate a star formation rate of 1.5e-3 msun/yr, resulting in a metal enrichment of ~1e-3 solar for the continuous formation of stars. Such systems may have been more common in the past and a similar enrichment level is measured for the `metallicity floor' in damped Lyman-alpha absorption systems.

The First Supernova Explosions in the Universe

We investigate the supernova explosions that end the lives of massive Population III stars in low-mass minihalos (M ~ 106 M☉) at redshifts z ~ 20. Employing the smoothed particle hydrodynamics method, we carry out numerical simulations in a cosmological setup of pair-instability supernovae with explosion energies of ESN = 1051 and 1053 ergs. Whereas the lower explosion energy leaves part of the halo intact, we find that the more energetic explosion leads to the complete disruption of the gas in the minihalo and expels 90% of the stellar metals into a region ~1 kpc across over a timescale of 3-5 Myr. Because of this burstlike initial star formation episode, a large fraction of the universe could have been endowed with a metallicity floor, Zmin 10-4 Z☉, already at z 15.

Linking the Metallicity Distribution of Galactic Halo Stars to the Enrichment History of the Universe

We compare the distribution of Galactic halo stars with three-dimensional realizations of hierarchical galaxy formation. Outflows from dwarf galaxies enrich the intergalactic medium inhomogeneously, at a rate depending on the local galaxy density. Consequently, the first stars created in small early-forming galaxies are less metal-rich than the first stars formed in more massive galaxies, which typically form later. As most halo stars are likely to originate in accreted dwarfs, while disk stars formed out of outflow-enriched gas, this scenario naturally generates a metallicity floor for old disk stars, which we find to be roughly coincident with the higher end of our predicted distribution of halo stars, in agreement with observations. The broad and centrally peaked distribution of halo star metallicities is well reproduced in our models, with a natural dispersion depending on the exact accretion history. Our modeling includes the important baryonic effect of early outflows, which brush away the tenuously held gas in neighboring previrialized density perturbations. This stripping process does not significantly modify the predicted shape of the halo star metal distribution but inhibits star formation and hence the number of accreted stars, helping to reconcile our model with the observed total Galactic halo luminosity and the lack of low-luminosity local dwarf galaxies relative to N-body predictions.

The Effect of Mats on the Welfare of Sows and Piglets in the Farrowing House

AbstractThe objective of this study was to assess the effect of providing mats in the farrowing pen on behaviour and lesions in sows (n = 38) and piglets. Nineteen of the sows and their litters housed in farrowing crates with metal slatted floors were provided with mats, the remaining 19 acting as controls. Sow skin was inspected pre-farrowing and at weaning: the skin and feet of piglets were examined when they were 6 days old. Skin lesions were scored (on a scale of 0 to 6) according to severity. Total lesion scores per sow and median total lesion scores per litter were calculated. Sow behaviour was recorded by direct observation at feeding. Usage of a heat pad for lying in the presence or absence of mats was assessed over a 2hr observation period. Median skin lesion scores of sows did not differ between treatments. Litters from the control treatment had lower skin lesion scores (median [range] 8 [2-12] vs 10 [5-21]; P &lt; 0.05). Median lesion scores of the front legs tended to be higher for piglets on mats (median [range] 8 [1.5-13] vs 4 [1.5-8]; ns). Sows on metal flooring went from kneeling to lowering their hindquarters faster (median [range] 15 [2—45] s) than sows on mats (23 [11—54] s) (P &lt; 0.05). Furthermore, they slipped more on their front (median [range] 2.7 [0-8.7] vs 0 [0-1.3] slips min1; P &lt; 0.001) and hind (median [range] 5.3 [0.3-31.7] vs 1.9 [0-33.3] slips min1; P &lt; 0.05) feet while standing, than sows on mats. More piglets lay on the heat pad when it was covered by a mat (mean ± SEM 45.97 ± 4.49 %) than when no mat was provided (29.29 ± 4.47 %)(P &lt; 0.05). Mats improve sow comfort and reduce slipping. They encourage piglets to lie on the heat pad but cause damage to the skin of the front legs. Providing pigs with mats in the farrowing house could greatly improve welfare on slatted floors, but further research is needed to identify materials that are less abrasive.