Control of the major African malaria vector species continues to rely extensively on the application of residual insecticides through indoor house spraying or bed net impregnation. Insecticide ...resistance is undermining the sustainability of these control strategies. Alternatives to the currently available conventional chemical insecticides are, therefore, urgently needed. Use of fungal pathogens as biopesticides is one such possibility. However, one of the challenges to the approach is the potential influence of varied environmental conditions and target species that could affect the efficacy of a biological 'active ingredient'. An initial investigation into this was carried out to assess the susceptibility of insecticide-susceptible and resistant laboratory strains and wild-collected Anopheles arabiensis mosquitoes to infection with the fungus Beauveria bassiana under two different laboratory temperature regimes.
Insecticide susceptibility to all four classes of insecticides recommended by WHO for vector control was tested on laboratory and wild-caught An. arabiensis, using standard WHO bioassay protocols. Mosquito susceptibility to fungus infection was tested using dry spores of B. bassiana under two temperature regimes (21 +/- 1 degrees C or 25 +/- 2 degrees C) representative of indoor conditions observed in western Kenya. Cox regression analysis was used to assess the effect of fungal infection on mosquito survival and the effect of insecticide resistance status and temperature on mortality rates following fungus infection.
Survival data showed no relationship between insecticide susceptibility and susceptibility to B. bassiana. All tested colonies showed complete susceptibility to fungal infection despite some showing high resistance levels to chemical insecticides. There was, however, a difference in fungus-induced mortality rates between temperature treatments with virulence significantly higher at 25 degrees C than 21 degrees C. Even so, because malaria parasite development is also known to slow as temperatures fall, expected reductions in malaria transmission potential due to fungal infection under the cooler conditions would still be high.
These results provide evidence that the entomopathogenic fungus B. bassiana has potential for use as an alternative vector control tool against insecticide-resistant mosquitoes under conditions typical of indoor resting environments. Nonetheless, the observed variation in effective virulence reveals the need for further study to optimize selection of isolates, dose and use strategy in different eco-epidemiological settings.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present the X-ray properties of 108 Dust-Obscured Galaxies (DOGs; F24 m/FR > 1000) in the COSMOS field, all of which are detected in at least three far-infrared bands with the Herschel ...Observatory. Out of the entire sample, 22 are individually detected in the hard 2-8 keV X-ray band by the Chandra COSMOS Legacy survey, allowing us to classify them as AGN. Six (27%) of them are Compton-thick AGN candidates with column densities NH > 1024 cm−2, while 15 are moderately obscured AGNs with 1022 < NH < 1024 cm−2. Additionally, we estimate AGN contributions to the IR luminosity (8-1000 m rest-frame) greater than 20% for 19 DOGs based on SED decomposition using Spitzer/MIPS 24 m and the five Herschel bands (100-500 m). Only 7 of these are detected in X-rays individually. We performed an X-ray stacking analysis for the 86 undetected DOGs. We find that the AGN fraction in DOGs increases with 24 m flux and that it is higher than that of the general 24 m population. However, no significant difference is found when considering only X-ray detections. This strongly motivates the combined use of X-ray and far-IR surveys to successfully probe a wider population of AGNs, particularly for the most obscured ones.
Abstract
We present a detailed weak-lensing and X-ray study of the Frontier Fields galaxy cluster Abell 370, one of the most massive known lenses on the sky, using wide-field
BR
C
z
′ ...Subaru/Suprime-Cam and Chandra X-ray observations. By combining two-dimensional (2D) shear and azimuthally averaged magnification constraints derived from Subaru data, we perform a lensing mass reconstruction in a free-form manner, which allows us to determine both the radial structure and 2D morphology of the cluster mass distribution. In a triaxial framework assuming a Navarro–Frenk–White density profile, we constrain the intrinsic structure and geometry of the cluster halo by forward modeling the reconstructed mass map. We obtain a halo mass
M
200
= (1.54 ± 0.29) ×10
15
h
−1
M
⊙
, a halo concentration
c
200
= 5.27 ± 1.28, and a minor–major axis ratio
q
a
= 0.62 ± 0.23 with uninformative priors. Using a prior on the line-of-sight alignment of the halo major axis derived from binary merger simulations constrained by multi-probe observations, we find that the data favor a more prolate geometry with lower mass and lower concentration. From triaxial lens modeling with the line-of-sight prior, we find a spherically enclosed gas mass fraction of
f
gas
= (8.4 ± 1.0)% at 0.7
h
−1
Mpc ∼ 0.7
r
500
. When compared to the hydrostatic mass estimate (
M
HE
) from Chandra observations, our triaxial weak-lensing analysis yields spherically enclosed mass ratios of 1 −
b
≡
M
HE
/
M
WL
= 0.56 ± 0.09 and 0.51 ± 0.09 at 0.7
h
−1
Mpc with and without using the line-of-sight prior, respectively. Since the cluster is in a highly disturbed dynamical state, this represents the likely maximum level of hydrostatic bias in galaxy clusters.
ABSTRACT We present estimates of intrinsic scatter in the star formation rate (SFR)-stellar mass (M*) correlation in the redshift range and in the mass range M . We utilize photometry in the Hubble ...Ultradeep Field (HUDF12) and Ultraviolet Ultra Deep Field (UVUDF) campaigns and CANDELS/GOODS-S and estimate SFR, M* from broadband spectral energy distributions and the best-available redshifts. The maximum depth of the UDF photometry (F160W 29.9 AB, 5 depth) probes the SFR-M* correlation down to 107M , a factor of 10-100× lower in M* than previous studies, and comparable to dwarf galaxies in the local universe. We find the slope of the SFR-M* relationship to be near unity at all redshifts and the normalization to decrease with cosmic time. We find a moderate increase in intrinsic scatter with cosmic time from 0.2 to 0.4 dex across the epoch of peak cosmic star formation. None of our redshift bins show a statistically significant increase in intrinsic scatter at low mass. However, it remains possible that intrinsic scatter increases at low mass on timescales shorter than ∼100 Myr. Our results are consistent with a picture of gradual and self-similar assembly of galaxies across more than three orders of magnitude in stellar mass from as low as 107M .
We present new results from our search for z ~ 7 galaxies from deep spectroscopic observations of candidate z dropouts in the CANDELS fields. Despite the extremely low flux limits achieved by our ...sensitive observations, only two galaxies have robust redshift identifications, one from its Ly alpha emission line at z = 6.65, the other from its Lyman break, i.e., the continuum discontinuity at the Ly alpha wavelength consistent with a redshift of 6.42 but with no emission line. In addition, for 23 galaxies we present deep limits in the Ly alpha equivalent width derived from the nondetections in ultradeep observations. Using this new data as well as previous samples, we assemble a total of 68 candidate z ~ 7 galaxies with deep spectroscopic observations, of which 12 have a line detection. With this much enlarged sample we can place solid constraints on the declining fraction of Ly alpha emission in z ~ 7 Lyman-break galaxies compared to z ~ 6, both for bright and faint galaxies. Applying a simple analytical model, we show that the present data favor a patchy reionization process rather than a smooth one.
The Hubble Ultra Deep Field Beckwith, Steven V. W; Stiavelli, Massimo; Koekemoer, Anton M ...
The Astronomical journal,
11/2006, Letnik:
132, Številka:
5
Journal Article
Recenzirano
Odprti dostop
This paper presents the Hubble Ultra Deep Field (HUDF), a 1 million s exposure of an 11 arcmin2 region in the southern sky with the Advanced Camera for Surveys on the Hubble Space Telescope using ...Director's Discretionary Time. The exposure time was divided among four filters, F435W (B435), F606W (V606), F775W (i 775), and F850LP (z850), to give approximately uniform limiting magnitudes mAB ~ 29 for point sources. The image contains at least 10,000 objects, presented here as a catalog, the vast majority of which are galaxies. Visual inspection of the images shows few if any galaxies at redshifts greater than ~4 that resemble present-day spiral or elliptical galaxies. The image reinforces the conclusion from the original Hubble Deep Field that galaxies evolved strongly during the first few billion years in the infancy of the universe. Using the Lyman break dropout method to derive samples of galaxies at redshifts between 4 and 7, it is possible to study the apparent evolution of the galaxy luminosity function and number density. Examination of the catalog for dropout sources yields 504 B435 dropouts, 204 V 606 dropouts, and 54 i775 dropouts. The i775 dropouts are most likely galaxies at redshifts between 6 and 7. Using these samples, which are at different redshifts but derived from the same data, we find no evidence for a change in the characteristic luminosity of galaxies but some evidence for a decrease in their number densities between redshifts of 4 and 7. Assessing the factors needed to derive the luminosity function from the data suggests that there is considerable uncertainty in parameters from samples discovered with different instruments and derived using independent assumptions about the source populations. This assessment calls into question some of the strong conclusions of recently published work on distant galaxies. The ultraviolet luminosity density of these samples is dominated by galaxies fainter than the characteristic luminosity, and the HUDF reveals considerably more luminosity than shallower surveys. The apparent ultraviolet luminosity density of galaxies appears to decrease from redshifts of a few to redshifts greater than 6, although this decrease may be the result of faint-end incompleteness in the most distant samples. The highest redshift samples show that star formation was already vigorous at the earliest epochs at which galaxies have been observed, less than 1 billion years after the big bang.
The second most significant detection of the Planck Sunyaev−Zel'dovich survey, PLCK G287.0+32.9 (z = 0.385), boasts two similarly bright radio relics and a radio halo. One radio relic is located NW ...of the X-ray peak and the other Mpc to the SE. This large difference suggests that a complex merging scenario is required. A key missing puzzle for the merging scenario reconstruction is the underlying dark matter distribution in high resolution. We present a joint Subaru Telescope and Hubble Space Telescope weak-lensing analysis of the cluster. Our analysis shows that the mass distribution features four significant substructures. Of the substructures, a primary cluster of mass dominates the weak-lensing signal. This cluster is likely to be undergoing a merger with one (or more) subcluster whose mass is approximately a factor of 10 lower. One candidate is the subcluster of mass located to the SE. The location of this subcluster suggests that its interaction with the primary cluster could be the source of the NW radio relic. Another subcluster is detected Mpc to the SE of the X-ray peak with mass . This SE subcluster is in the vicinity of the SE radio relic and may have created the SE radio relic during a past merger with the primary cluster. The fourth subcluster, , is NW of the X-ray peak and beyond the NW radio relic.
We analyze the environments and galactic properties (morphologies and star formation histories) of a sample of 153 close kinematic pairs in the redshift range 0.2 < z < 1 identified in the ...zCOSMOS-bright 10k spectroscopic sample of galaxies. We then examine the morphologies and stellar populations of galaxies in the pairs, comparing them to control samples that are carefully matched in environment so as to remove as much of the well-known effects of environment on the properties of the parent population of galaxies as possible. Once the environment is properly taken into account in this way, we find that the early-late morphology mix is the same as for the parent population, but that the fraction of irregular galaxies is boosted by 50%-75%, with a disproportionate increase in the number of irregular-irregular pairs (factor of 4-8 times), due to the disturbance of disk galaxies.
This paper studies the properties of kiloparsec-scale clumps in star-forming galaxies at z similar to 2 through multi-wavelength broadband photometry. A sample of 40 clumps is identified from Hubble ...Space Telescope (HST)/Advanced Camera for Surveys (ACS) z-band images through auto-detection and visual inspection from 10 galaxies with 1.5 \textless z \textless 2.5 in the Hubble Ultra Deep Field, where deep and high-resolution HST/WFC3 and ACS images enable us to resolve structures of z similar to 2 galaxies down to the kiloparsec scale in the rest-frame UV and optical bands and to detect clumps toward the faint end. The physical properties of clumps are measured through fitting spatially resolved seven-band (BVizYJH) spectral energy distribution to models. On average, the clumps are blue and have similar median rest-frame UV-optical color as the diffuse components of their host galaxies, but the clumps have large scatter in their colors. Although the star formation rate (SFR)-stellar mass relation of galaxies is dominated by the diffuse components, clumps emerge as regions with enhanced specific star formation rates, contributing individually similar to 10% and together similar to 50% of the SFR of the host galaxies. However, the contributions of clumps to the rest-frame UV/optical luminosity and stellar mass are smaller, typically a few percent individually and similar to 20% together. On average, clumps are younger by 0.2 dex and denser by a factor of eight than diffuse components. Clump properties have obvious radial variations in the sense that central clumps are redder, older, more extincted, denser, and less active on forming stars than outskirt clumps. Our results are broadly consistent with a widely held view that clumps are formed through gravitational instability in gas-rich turbulent disks and would eventually migrate toward galactic centers and coalesce into bulges. Roughly 40% of the galaxies in our sample contain a massive clump that could be identified as a proto-bulge, which seems qualitatively consistent with such a bulge-formation scenario.
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