5,305 research outputs found
The Size and Origin of Metal-enriched Regions in the Intergalactic Medium from Spectra of Binary Quasars
We present tomography of the circum-galactic metal distribution at redshift 1.7-4.5 derived from echellete spectroscopy of binary quasars. We find C IV systems at similar redshifts in paired sightlines more often than expected for sightline-independent redshifts. As the separation of the sightlines increases from 36 kpc to 907 kpc, the amplitude of this clustering decreases. At the largest separations, the C IV systems cluster similar to the Lyman-break galaxies studied by Adelberger et al. in 2005. The C IV systems are significantly less correlated than these galaxies, however, at separations less than R_1 0.42 ± 0.15 h^( –1) comoving Mpc. Measured in real space, i.e., transverse to the sightlines, this length scale is significantly smaller than the break scale estimated previously from the line-of-sight correlation function in redshift space by Scannapieco et al. in 2006. Using a simple model, we interpret the new real-space measurement as an indication of the typical physical size of enriched regions. We adopt this size for enriched regions and fit the redshift-space distortion in the line-of-sight correlation function. The fitted velocity kick is consistent with the peculiar velocity of galaxies as determined by the underlying mass distribution and places an upper limit on the average outflow (or inflow) speed of metals. The implied timescale for dispersing metals is larger than the typical stellar ages of Lyman-break galaxies, and we argue that enrichment by galaxies at z > 4.3 played a greater role in dispersing metals. To further constrain the growth of enriched regions, we discuss empirical constraints on the evolution of the C IV correlation function with cosmic time. This study demonstrates the potential of tomography for measuring the metal enrichment history of the circum-galactic medium
Ionized Gas Motions and the Structure of Feedback Near a Forming Globular Cluster in NGC 5253
We observed Brackett 4.05m emission towards the supernebula in
NGC 5253 with NIRSPEC on Keck II in adaptive optics mode, NIRSPAO, to probe
feedback from its exciting embedded super star cluster (SSC). NIRSPEC's
Slit-Viewing Camera was simultaneously used to image the K-band continuum at
resolution. We register the IR continuum with HST imaging, and
find that the visible clusters are offset from the K-band peak, which coincides
with the Br peak of the supernebula and its associated molecular
cloud. The spectra of the supernebula exhibit Br emission with a
strong, narrow core. The linewidths are 65-76 km s, FWHM, comparable to
those around individual ultra-compact HII regions within our Galaxy. A weak,
broad (FWHM150-175 km s) component is detected on the base of
the line, which could trace a population of sources with high-velocity winds.
The core velocity of Br emission shifts by +13 km s from NE to
SW across the supernebula, possibly indicating a bipolar outflow from an
embedded object, or linked to a foreground redshifted gas filament. The results
can be explained if the supernebula comprises thousands of ionized wind regions
around individual massive stars, stalled in their expansion due to critical
radiative cooling and unable to merge to drive a coherent cluster wind. Based
on the absence of an outflow with large mass loss, we conclude that feedback is
currently ineffective at dispersing gas, and the SSC retains enriched material
out of which it may continue to form stars.Comment: 24 pages, 9 figure
Governance and Capacity to Manage Resilience of Health Systems: Towards a New Conceptual Framework.
The term resilience has dominated the discourse among health systems researchers since 2014 and the onset of the Ebola outbreak in West Africa. There is wide consensus that the global community has to help build more resilient health systems. But do we really know what resilience means, and do we all have the same vision of resilience? The present paper presents a new conceptual framework on governance of resilience based on systems thinking and complexity theories. In this paper, we see resilience of a health system as its capacity to absorb, adapt and transform when exposed to a shock such as a pandemic, natural disaster or armed conflict and still retain the same control over its structure and functions
Tree Responses to an Invasive Sap-Feeding Insect
Although sap-feeding insects are known to negatively affect plant growth and physiology, less is known about sap-feeding insects on woody plants. Adelges tsugae (Annand Hemiptera: Adelgidae), the hemlock woolly adelgid, is an invasive sap-feeding insect in eastern North America that feeds on and kills Tsuga canadensis (L. Carrière), eastern hemlock. Newly hatched adelgid nymphs crawl to young unattacked tissue, settle and immediately enter diapause (aestivation) while attached to hemlock in summer. We assessed the effect of A. tsugae infestation on T. canadensis growth and physiology by analyzing hemlock growth on lateral and terminal branches, water potential, photosynthesis, stomatal conductance, and foliar nitrogen (%N). A. tsugae infestation greatly decreased terminal and lateral growth of eastern hemlock. In addition, A. tsugae presence reduced photosynthesis by 10 % in September and 36 % in October. Adelgid-infested hemlocks also exhibited signs of water stress that included notable reductions in water potential and stomatal conductance. These responses shed light on possible mechanisms of adelgid-induced mortality
Galaxy mergers moulding the circum-galactic medium - I. The impact of a major merger
Galaxies are surrounded by sizeable gas reservoirs which host a significant
amount of metals: the circum-galactic medium (CGM). The CGM acts as a mediator
between the galaxy and the extra-galactic medium. However, our understanding of
how galaxy mergers, a major evolutionary transformation, impact the CGM remains
deficient. We present a theoretical study of the effect of galaxy mergers on
the CGM. We use hydrodynamical cosmological zoom-in simulations of a major
merger selected from the Illustris project such that the z=0 descendant has a
halo mass and stellar mass comparable to the Milky Way. To study the CGM we
then re-simulated this system at a 40 times better mass resolution, and
included detailed post-processing ionization modelling. Our work demonstrates
the effect the merger has on the characteristic size of the CGM, its
metallicity, and the predicted covering fraction of various commonly observed
gas-phase species, such as H I, C IV, and O VI. We show that merger-induced
outflows can increase the CGM metallicity by 0.2-0.3 dex within 0.5 Gyr
post-merger. These effects last up to 6 Gyr post-merger. While the merger
increases the total metal covering fractions by factors of 2-3, the covering
fractions of commonly observed UV ions decrease due to the hard ionizing
radiation from the active galactic nucleus, which we model explicitly. Our
study of the single simulated major merger presented in this work demonstrates
the significant impact that a galaxy interaction can have on the size,
metallicity, and observed column densities of the CGM
Transverse Sizes of CIV Absorption Systems Measured from Multiple QSO Sightlines
We present tomography of the circum-galactic metal distribution at redshift
1.7 to 4.5 derived from echellete spectroscopy of binary quasars. We find CIV
systems at similar redshifts in paired sightlines more often than expected for
sightline-independent redshifts. As the separation of the sightlines increases
from 36 kpc to 907 kpc, the amplitude of this clustering decreases. At the
largest separations, the CIV systems cluster similar to Lyman-break galaxies
(Adelberger et al. 2005a). The CIV systems are significantly less correlated
than these galaxies, however, at separations less than R_1 ~ 0.42 +/- 0.15 h-1
comoving Mpc. Measured in real space, i.e., transverse to the sightlines, this
length scale is significantly smaller than the break scale estimated from the
line-of-sight correlation function in redshift space (Scannapieco et al.
2006a). Using a simple model, we interpret the new real-space measurement as an
indication of the typical physical size of enriched regions. We adopt this size
for enriched regions and fit the redshift-space distortion in the line-of-sight
correlation function. The fitted velocity kick is consistent with the peculiar
velocity of galaxies as determined by the underlying mass distribution and
places an upper limit on the outflow (or inflow) speed of metals. The implied
time scale for dispersing metals is larger than the typical stellar ages of
Lyman-break galaxies (Shapley et al. 2001), and we argue that enrichment by
galaxies at z > 4.3 played a greater role in dispersing metals. To further
constrain the growth of enriched regions, we discuss empirical constraints on
the evolution of the CIV correlation function with cosmic time. This study
demonstrates the potential of tomography for measuring the metal enrichment
history of the circum-galactic medium.Comment: 22 pages, 15 figures, 1 tabl
Seasonal variation in effects of herbivory on foliar nitrogen of a threatened conifer
Invasive herbivores can dramatically impact the nitrogen (N) economy of native hosts. In deciduous species, most N is stored in stem tissues, while in evergreen conifer species N is stored in needles, making them potentially more vulnerable to herbivory. In eastern forests of the USA, the long-lived, foundational conifer eastern hemlock (Tsuga canadensis) is under the threat of extirpation by the invasive hemlock woolly adelgid (HWA: Adelges tsugae). We assessed the impact of HWA infestation on the patterns of seasonal foliar N availability in hemlock planted in a deciduous forest understory. Over the course of a year, we sampled needles and twigs and measured N, carbon (C), C:N ratio, and total protein concentrations. Tissue sampling events were timed to coincide with key life-history transitions for HWA to determine the association between HWA development and feeding with these foliar nutrients. In uninfested trees, needle and twig N concentrations fluctuated across seasons, indicating the potential importance of N storage and remobilization for the N economy of eastern hemlock. Although N levels in HWA-infested trees also cycled annually, the degree to which N concentrations fluctuated seasonally in tissues was significantly affected by HWA feeding. These fluctuations exceeded N levels observed in control trees and coincided with HWA feeding. HWA feeding generally increased N concentrations but did not affect protein levels, suggesting that changes in N do not occur via adelgid-induced protein breakdown. Herbivore-induced mobilization of N to feeding sites and its rapid depletion may be a significant contributor to eastern hemlock mortality in US forests
Isolation of a Wickerhamomyces anomalus yeast strain from the sandfly Phlebotomus perniciosus, displaying the killer phenotype
The yeast Wickerhamomyces anomalus has been studied for its wide biotechnological potential, mainly for applications in the food industry. Different strains of W. anomalus have been isolated from diverse habitats and recently from insects, including mosquitoes of medical importance. This paper reports the isolation and phylogenetic characterization of W. anomalus from laboratory-reared adults and larvae of Phlebotomus perniciosus (Diptera: Psychodidae), a main phlebotomine vector of human and canine leishmaniasis. Of 65 yeast strains isolated from P. perniciosus, 15 strains were identified as W. anomalus; one of these was tested for the killer phenotype and demonstrated inhibitory activity against four yeast sensitive strains, as reported for mosquito-isolated strains. The association between P. perniciosus and W. anomalus deserves further investigation in order to explore the possibility that this yeast may exert inhibitory/killing activity against Leishmania spp
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