278 research outputs found
Lyman Break Analogs: Constraints on the Formation of Extreme Starbursts at Low and High Redshift
Lyman Break Analogs (LBAs), characterized by high far-UV luminosities and
surface brightnesses as detected by GALEX, are intensely star-forming galaxies
in the low-redshift universe (), with star formation rates reaching
up to 50 times that of the Milky Way. These objects present metallicities,
morphologies and other physical properties similar to higher redshift Lyman
Break Galaxies (LBGs), motivating the detailed study of LBAs as local
laboratories of this high-redshift galaxy population. We present results from
our recent integral-field spectroscopy survey of LBAs with Keck/OSIRIS, which
shows that these galaxies have the same nebular gas kinematic properties as
high-redshift LBGs. We argue that such kinematic studies alone are not an
appropriate diagnostic to rule out merger events as the trigger for the
observed starburst. Comparison between the kinematic analysis and morphological
indices from HST imaging illustrates the difficulties of properly identifying
(minor or major) merger events, with no clear correlation between the results
using either of the two methods. Artificial redshifting of our data indicates
that this problem becomes even worse at high redshift due to surface brightness
dimming and resolution loss. Whether mergers could generate the observed
kinematic properties is strongly dependent on gas fractions in these galaxies.
We present preliminary results of a CARMA survey for LBAs and discuss the
implications of the inferred molecular gas masses for formation models.Comment: To appear in the proceedings of IAU Symposium 277, "Tracing the
Ancestry of Galaxies on the Land of our Ancestors", eds. C. Carignan, K.C.
Freeman, and F. Combe
Interglacials of the Quaternary defined by northern hemispheric land ice distribution outside of Greenland
Glacial/interglacial dynamics during the Quaternary were suggested to be mainly driven by obliquity (41-kyr periodicity), including irregularities during the last 1 Myr that resulted in on average 100-kyr cycles. Here, we investigate this so-called Mid-Pleistocene Transition via model-based deconvolution of benthic δ18O, redefining interglacials by lack of substantial northern hemispheric land ice outside of Greenland. We find that in 67%, 88% and 52% of the obliquity cycles during the early, middle and late Quaternary, respectively, a glacial termination is realized leading to irregular appearances of new interglacials during various parts of the last 2.6 Myr. This finding suggests that the proposed idea of terminations leading to new interglacials in the Quaternary as obliquity driven with growing influence of land ice volume on the timing of deglaciations during the last 1 Myr might be too simple. Alternatively, the land ice-based definition of interglacials needs revision if applied to the entire Quaternary
Big Changes in How Students are Tested
For the past decade, school accountability has relied on tests for which the essential format has remained unchanged. Educators are familiar with the yearly testing routine: schools are given curriculum frameworks, teachers use the frameworks to guide instruction, students take one big test at year’s end which relies heavily upon multiple-choice bubble items, and then school leaders wait anxiously to find out whether enough of their students scored at or above proficiency to meet state standards. All this will change with the adoption of Common Core standards. Testing and accountability aren’t going away. Instead, they are developing and expanding in ways that aim to address many of the present shortcomings of state testing routines. Most importantly, these new tests will be computer-based. As such, they will potentially shorten testing time, increase tests’ precision, and provide immediate feedback to students and teachers
Evidence for Elevated X-ray Emission in Local Lyman Break Galaxy Analogs
In this paper, we study the relationship between the 2-10 keV X-ray
luminosity (L_X), assumed to originate from X-ray binaries (XRBs), and star
formation rate (SFR) in UV-selected z<0.1 Lyman break analogs (LBAs). We
present Chandra observations for four new GALEX-selected LBAs. Including
previously studied LBAs, Haro 11 and VV 114, we find that LBAs demonstrate
L_X/SFR ratios that are elevated by ~1.5sigma compared to local galaxies,
similar to the ratios found for stacked LBGs in the early Universe (z>2). We
show that these LBAs are unlikely to harbor AGN, based on their optical and
X-ray spectra and the spatial distribution of the X-rays in three spatially
extended cases. We expect that high-mass X-ray binaries (HMXBs) dominate the
X-ray emission in these galaxies, based on their high specific SFRs
(sSFRs=SFR/M* > 10^{-9}/yr), which suggest the prevalence of young stellar
populations. Since both LBAs and LBGs have lower dust attenuations and
metallicities compared to similar samples of more typical local galaxies, we
investigate the effects of dust extinction and metallicity on the L_X/SFR for
the broader population of galaxies with high sSFRs (>10^{-10}/yr). The
estimated dust extinctions (corresponding to column densities of
N_H<10^{22}/cm^2) are expected to have insignificant effects on observed
L_X/SFR ratio for the majority of galaxy samples. We find that the observed
relationship between L_X/SFR and metallicity appears consistent with
theoretical expectations from X-ray binary population synthesis models.
Therefore, we conclude that lower metallicities, related to more luminous HMXBs
such as ultraluminous X-ray sources (ULXs), drive the elevated L_X/SFR observed
in our sample of z<0.1 LBAs. The relatively metal-poor, active mode of star
formation in LBAs and distant z>2 LBGs may yield higher total HMXB luminosity
than found in typical galaxies in the local Universe.Comment: 11 pages, 7 figures, Submitted to ApJ (references updated in v2
Climatic suitability ranking of biological control candidates: a biogeographic approach for ragweed management in Europe
Biological control using natural antagonists has been a most successful management tool against alien invasive plants that threaten biodiversity. The selection of candidate agents remains a critical step in a biocontrol program before more elaborate and time-consuming experiments are conducted. Here, we propose a biogeographic approach to identify candidates and combinations of candidates to potentially cover a large range of the invader. We studied Ambrosia artemisiifolia (common ragweed), native to North America (NA) and invasive worldwide, and six NA biocontrol candidates for the introduced Europe (EU) range of ragweed, both under current and future bioclimatic conditions. For the first time, we constructed species distribution models based on worldwide occurrences and important bioclimatic variables simultaneously for a plant invader and its biocontrol candidates in view of selecting candidates that potentially cover a large range of the target invader. Ordination techniques were used to explore climatic constraints of each species and to perform niche overlap tests with ragweed. We show a large overlap in climatic space between candidates and ragweed, but a considerable discrepancy in geographic range overlap between EU (31.4%) and NA (83.3%). This might be due to niche unfilling and expansion of ragweed in EU and the fact that habitats with high ragweed occurrences in EU are rare in NA and predicted to be unsuitable for the candidates. Total geographic range of all candidates combined is expected to decrease under climate change in both ranges, but they will respond differently. The relative geographic coverage of a plant invader by biocontrol candidates at home is largely transferable to the introduced range, even when the invader shifts its niche. Our analyses also identified which combination of candidates is expected to cover the most area and for which abiotic conditions to select in order to develop climatically adapted strains for particular regions, where ragweed is currently unlikely to be controlled
The kinematics of ionized gas in lyman-break analogs at z ~ 0.2
We present results for 19 “Lyman-break analogs” observed with Keck/OSIRIS with an adaptive-optics-assisted
spatial resolution of less than 200 pc. We detect satellites/companions, diffuse emission, and velocity shear, all
with high signal-to-noise ratios. These galaxies present remarkably high velocity dispersion along the line of sight
(~70 km s^(−1)), much higher than standard star-forming spirals in the low-redshift universe. We artificially redshift
our data to z ~ 2.2 to allow for a direct comparison with observations of high-z Lyman-break galaxies and find
striking similarities between both samples. This suggests that either similar physical processes are responsible
for their observed properties, or, alternatively, that it is very difficult to distinguish between different mechanisms
operating in the low- versus high-redshift starburst galaxies based on the available data. The comparison between
morphologies in the UV/optical continuum and our kinemetry analysis often shows that neither is by itself sufficient
to confirm or completely rule out the contribution from recent merger events. We find a correlation between the
kinematic properties and stellar mass, in that more massive galaxies show stronger evidence for a disk-like structure.
This suggests a co-evolutionary process between the stellar mass buildup and the formation of morphological and
dynamical substructure within the galaxy
Breath of Life: The Respiratory Vagal Stimulation Model of Contemplative Activity
Contemplative practices, such as meditation and yoga, are increasingly popular among the general public and as topics of research. Beneficial effects associated with these practices have been found on physical health, mental health and cognitive performance. However, studies and theories that clarify the underlying mechanisms are lacking or scarce. This theoretical review aims to address and compensate this scarcity. We will show that various contemplative activities have in common that breathing is regulated or attentively guided. This respiratory discipline in turn could parsimoniously explain the physical and mental benefits of contemplative activities through changes in autonomic balance. We propose a neurophysiological model that explains how these specific respiration styles could operate, by phasically and tonically stimulating the vagal nerve: respiratory vagal nerve stimulation (rVNS). The vagal nerve, as a proponent of the parasympathetic nervous system (PNS), is the prime candidate in explaining the effects of contemplative practices on health, mental health and cognition. We will discuss implications and limitations of our model
Minimising medicine use in organic dairy herds through animal health and welfare planning
Livestock is important in many organic farming systems, and it is an explicit goal to ensure high levels of animal health and welfare (AHW) through good management. This will lead to reduced medicine use and better quality of animal products. In two EU network projects NAHWOA & SAFO it was concluded that this is not guaranteed merely by following organic standards. Both networks recommended implementation of individual animal health plans to stimulate organic farmers to improve AHW. These plans should include a systematic evaluation of AHW and be implemented through dialogue with each farmer in order to identify goals and plan improvements. 15 research institutions in 8 European countries are involved in the proposed project with the main objective to minimise medicine use in organic dairy herds through active and well planned AHW promotion and disease prevention. The project consists of 5 work packages, 4 of which comprise research activities building on current research projects, new applications across borders, exchange of knowledge, results and conclusions between participating countries, and adopting them to widely different contexts. International and national workshops facilitate this exchange. Focus areas are animal health planning, AHW assessment using animal based parameters and development of advisory systems and farmer groups. Epidemiological analyses of the effect on AHW from reduced medicine use and herd improvements are planned in all participating countries
Modelling present-day basal melt rates for Antarctic ice shelves using a parametrization of buoyant meltwater plumes
Basal melting below ice shelves is a major factor
in mass loss from the Antarctic Ice Sheet, which can contribute
significantly to possible future sea-level rise. Therefore,
it is important to have an adequate description of the
basal melt rates for use in ice-dynamical models. Most current
ice models use rather simple parametrizations based on
the local balance of heat between ice and ocean. In this
work, however, we use a recently derived parametrization of
the melt rates based on a buoyant meltwater plume travelling
upward beneath an ice shelf. This plume parametrization
combines a non-linear ocean temperature sensitivity with an
inherent geometry dependence, which is mainly described
by the grounding-line depth and the local slope of the iceshelf
base. For the first time, this type of parametrization
is evaluated on a two-dimensional grid covering the entire
Antarctic continent. In order to apply the essentially onedimensional
parametrization to realistic ice-shelf geometries,
we present an algorithm that determines effective values for
the grounding-line depth and basal slope in any point beneath
an ice shelf. Furthermore, since detailed knowledge of
temperatures and circulation patterns in the ice-shelf cavities
is sparse or absent, we construct an effective ocean temperature
field from observational data with the purpose of
matching (area-averaged) melt rates from the model with observed
present-day melt rates. Our results qualitatively replicate
large-scale observed features in basal melt rates around
Antarctica, not only in terms of average values, but also in
terms of the spatial pattern, with high melt rates typically occurring
near the grounding line. The plume parametrization
and the effective temperature field presented here are therefore
promising tools for future simulations of the Antarctic
Ice Sheet requiring a more realistic oceanic forcing
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