Segue 1 - A Compressed Star Formation History Before Reionization

Segue 1 is the current best candidate for a "first galaxy", a system which experienced only a single short burst of star formation and has since remained unchanged. Here we present possible star formation scenarios which can explain its unique metallicity distribution. While the majority of stars in all other ultra-faint dwarfs (UFDs) are within 0.5 dex of the mean [Fe/H] for the galaxy, 5 of the 7 stars in Segue 1 have a spread of $\Delta$[Fe/H] $>0.8$ dex. We show that this distribution of metallicities canot be explained by a gradual build-up of stars, but instead requires clustered star formation. Chemical tagging allows the separate unresolved delta functions in abundance space to be associated with discrete events in space and time. This provides an opportunity to put the enrichment events into a time sequence and unravel the history of the system. We investigate two possible scenarios for the star formation history of Segue 1 using Fyris Alpha simulations of gas in a $10^7$ M$_\odot$ dark matter halo. The lack of stars with intermediate metallicities $-3<$ [Fe/H] $<-2$ can be explained either by a pause in star formation caused by supernova feedback, or by the spread of metallicities resulting from one or two supernovae in a low-mass dark matter halo. Either possibility can reproduce the metallicity distribution function (MDF), as well as the other observed elemental abundances. The unusual MDF and the low luminosity of Segue 1 can be explained by it being a first galaxy that originated with $M_{\rm{vir}}\sim10^7$~M$_\odot$ at $z\sim10$.Comment: 12 pages, 6 figures, ApJ, Accepte

Ultrafaint Dwarf Galaxies - the lowest mass relics from before reionization

New observations indicate that ultrafaint dwarf galaxies (UFD) -- the least luminous systems bound by dark matter halos (<10^5 Lsun) -- may have formed before reionization. The extrapolated virial masses today are uncertain with estimates ranging from 10^8 Msun to 10^9 Msun. We show that the progenitor halo masses of UFDs can be as low as Mvir = 10^7 Msun. Under the right conditions, such a halo can survive the energy input of a supernova and its radiative progenitor. A clumpy medium is much less susceptible to both internal and external injections of energy. It is less prone to SN sweeping because the coupling efficiency of the explosive energy is much lower than for a diffuse ISM. With the aid of the 3D hydro/ionization code Fyris, we show that sufficient baryons are retained to form stars following a single supernova event in dark matter halos down to Mvir ~ 10^7 Msun with radiative cooling. The gas survives the SN explosion, is enriched with the abundance yields of the discrete events, and reaches surface densities where low mass stars can form. Our highest resolution simulations reveal why cooling is so effective in retaining gas compared to any other factor. In the early stages, the super-hot metal-enriched SN ejecta exhibit strong cooling, leading to much of the explosive energy being lost. Consistent with earlier work, the baryons do *not* survive in smooth or adiabatic models in the event of a supernova. The smallest galaxies carry signatures of the earliest epochs of star formation, which may distinguish a small primordial galaxy from one that was stripped down to its present size through tidal interaction. We discuss these results in the context of local UFDs and damped Ly-alpha systems (z~2) at very low metallicity ([Fe/H] ~ -3). We show that both classes of objects are consistent with primordial low-mass systems that have experienced only a few enrichment events.Comment: 32 pages, 25 figures, accepted by Ap

Ultrafaint Dwarfs - Star Formation and Chemical Evolution in the Smallest Galaxies

In earlier work we showed that a dark matter halo with a virial mass of $10^7$ M$_\odot$ can retain a large percentage of its baryons in the face of the pre-ionization phase and supernova explosion from a 25$M_\odot$ star. Here we expand on the results of that work, investigating the star formation and chemical evolution of the system beyond the first supernova. In a galaxy with a mass $M_{vir} = 10^7$M$_\odot$, sufficient gas is retained by the potential for a second period of star formation to occur. The impact of a central explosion is found to be much stronger than that of an off-centred explosion both in blowing out the gas and in enriching it, as in the off-centered case most of the supernova energy and metals escape into the IGM. We model the star formation and metallicity given the assumption that stars form for 100, 200, 400 and 600 Myr and discuss the results in the context of recent observations of very low mass galaxies. We show that we can account for most features of the observed relationship between [$\alpha$/Fe] and [Fe/H] in ultra-faint dwarf galaxies with the assumption that the systems formed at a low mass, rather than being remnants of much larger systems

Using grounded theory to inform the design of energy interventions for the workplace

Much work has been published on using technological interventions to motivate reductions in home energy consumption. These interventions have produced promising results, but typically focus on emphasising the financial benefits of reductions in consumption to users. Motivating employees to reduce their consumption of energy in the workplace is more problematic, as they are typically not responsible for energy costs. There has been very little work to date addressing energy interventions in the workplace, and indeed, there are many challenges in doing so. This paper presents an overview of the initial user-centred design stage of a large energy research project called Electro-Magnates. Three day-long workshops were run with a total of 65 participants from 5 universities and a number of representatives from industry. The workshops’ main focus was understanding behaviour change in organisations in an energy resource and usage context, supported by designing a 12 month intervention. Audio and design task accounts were transcribed and analysed using the grounded theory approach with the developed theory forming the design requirements and implications for the Electro-Magnates intervention software. Our findings identified some of the key concepts for inclusion in a workplace energy intervention; incentivisation, openness and management buy-in

Star formation in ultra-faint dwarfs: continuous or single-aged bursts?

We model the chemical evolution of six ultra-faint dwarfs (UFDs): Bootes I, Canes Venatici II, Coma Berenices, Hercules, Leo IV, and Ursa Major I based on their recently determined star formation histories. We show that two single-age bursts cannot explain the observed [α/Fe] versus [Fe/H] distribution in these galaxies and that some selfenrichment is required within the first burst. An alternative scenario is modeled, in which star formation is continuous except for short interruptions when one or more supernovae temporarily blow the dense gas out from the center of the system. This model allows for self-enrichment and can reproduce the chemical abundances of the UFDs in which the second burst is only a trace population. We conclude that the most likely star formation history is one or two extended periods of star formation, with the first burst lasting for at least 100 Myr. As found in earlier work, the observed properties of UFDs can be explained by formation at a low mass (Mvir ~ 107 Me), rather than being stripped remnants of much larger systems.D.W. is funded by an Australian Postgraduate Award. J.B.H. is funded by an ARC Laureate Fellowship

The Chemical Evolution of Very Metal-Poor Damped LYα Systems

In earlier work we showed that a dark matter halo with a virial mass of 107 M⊙ can survive feedback from its own massive stars and form stars for ≳100 Myr. We also found that our modeled systems were consistent with observations of ultrafaint dwarfs

Microbial residence time is a controlling parameter of the taxonomic composition and functional profile of microbial communities.

A remaining challenge within microbial ecology is to understand the determinants of richness and diversity observed in environmental microbial communities. In a range of systems, including activated sludge bioreactors, the microbial residence time (MRT) has been previously shown to shape the microbial community composition. However, the physiological and ecological mechanisms driving this influence have remained unclear. Here, this relationship is explored by analyzing an activated sludge system fed with municipal wastewater. Using a model designed in this study based on Monod-growth kinetics, longer MRTs were shown to increase the range of growth parameters that enable persistence, resulting in increased richness and diversity in the modeled community. In laboratory experiments, six sequencing batch reactors treating domestic wastewater were operated in parallel at MRTs between 1 and 15 days. The communities were characterized using both 16S ribosomal RNA and non-target messenger RNA sequencing (metatranscriptomic analysis), and model-predicted monotonic increases in richness were confirmed in both profiles. Accordingly, taxonomic Shannon diversity also increased with MRT. In contrast, the diversity in enzyme class annotations resulting from the metatranscriptomic analysis displayed a non-monotonic trend over the MRT gradient. Disproportionately high abundances of transcripts encoding for rarer enzymes occur at longer MRTs and lead to the disconnect between taxonomic and functional diversity profiles

DAzLE: The Dark Ages z (redshift) Lyman-alpha Explorer

DAzLE is an near infrared narrowband differential imager being built by the Institute of Astronomy, Cambridge, in collaboration with the Anglo-Australian observatory. It is a special purpose instrument designed with a sole aim; the detection of redshifted Lyman-alpha emission from star forming galaxies at z>7. DAzLE will use pairs of high resolution (R=1000) narrowband filters to exploit low background `windows' in the near infrared sky emission spectrum. This will enable it to reach sensitivities of ~2E-21 W/m^2, thereby allowing the detection of z>7 galaxies with star formation rates as low as a few solar masses per year. The design of the instrument, and in particular the crucial narrowband filters, are presented. The predicted performance of DAzLE, including the sensitivity, volume coverage and expected number counts, is discussed. The current status of the DAzLE project, and its projected timeline, are also presented.Comment: 11 pages, 7 figures, to appear in Proceedings of SPIE Vol. 5492, Ground-based Instrumentation for Astronom

Translation resources and translator disempowerment

Language resources used for machine translation are created by human translators. These translators have legal rights with regard to copyright ownership of translated texts and databases of parallel bilingual texts, but may not be in a position to assert these rights due to employment practices widespread in the translation industry. This paper examines these employment practices in detail, and looks at the legal situation for ownership of translation resources. It also considers the situation from the standpoint of current owners of resources