We investigate the environmental quenching of galaxies, especially those with stellar masses (M*) < 109.5 M , beyond the local universe. Essentially all local low-mass quenched galaxies (QGs) are ...believed to live close to massive central galaxies, which is a demonstration of environmental quenching. We use CANDELS data to test whether or not such a dwarf QG-massive central galaxy connection exists beyond the local universe. For this purpose, we only need a statistically representative, rather than complete, sample of low-mass galaxies, which enables our study to z 1.5. For each low-mass galaxy, we measure the projected distance (dproj) to its nearest massive neighbor (M* > 1010.5 M ) within a redshift range. At a given z and M*, the environmental quenching effect is considered to be observed if the dproj distribution of QGs ( ) is significantly skewed toward lower values than that of star-forming galaxies ( ). For galaxies with 108 M < M* < 1010 M , such a difference between and is detected up to z ∼ 1. Also, about 10% of the quenched galaxies in our sample are located between two and four virial radii (RVir) of the massive halos. The median projected distance from low-mass QGs to their massive neighbors, , decreases with satellite M* at M* 109.5 M , but increases with satellite M* at M* 109.5 M . This trend suggests a smooth, if any, transition of the quenching timescale around M* ∼ 109.5 M at 0.5 < z < 1.0.
We investigate the stellar structure of massive, quiescent galaxies at z ~ 2, based on Hubble Space Telescope/WFC3 imaging from the Early Release Science program. Our sample of 14 galaxies has ...stellar masses of M * > 1010.8 M and photometric redshifts of 1.5 < z < 2.5. In agreement with previous work, their half-light radii are <2 kpc, much smaller than equally massive galaxies in the present-day universe. A significant subset of the sample appears highly flattened in projection, which implies, considering viewing angle statistics, that a significant fraction of the galaxies in our sample have pronounced disks. This is corroborated by two-dimensional surface brightness profile fits. We estimate that 65% ? 15% of the population of massive, quiescent z ~ 2 galaxies are disk dominated. The median disk scale length is 1.5 kpc, substantially smaller than the disks of equally massive galaxies in the present-day universe. Our results provide strong observational evidence that the much-discussed ultra-dense high-redshift galaxies should generally be thought of as disk-like stellar systems with the majority of stars formed from gas that had time to settle into a disk.
Abstract
Background
Malaria transmission can be highly heterogeneous between and within localities, and is influenced by factors such as survival and biting frequencies of
Anopheles
mosquitoes. This ...study investigated the relationships between the biological age, distance from aquatic habitats and pyrethroid resistance status of
Anopheles funestus
mosquitoes, which currently dominate malaria transmission in south-east Tanzania. The study also examined how such relationships may influence malaria transmission and control.
Methods
Female
An. funestus
were collected in houses located 50–100 m, 150–200 m or over 200 m from the nearest known aquatic habitats. The mosquitoes were exposed to 1×, 5× and 10× the diagnostic doses of deltamethrin or permethrin, or to the synergist, piperonyl butoxide (PBO) followed by the pyrethroids, then monitored for 24 h-mortality. Ovaries of exposed and non-exposed mosquitoes were dissected to assess parity as a proxy for biological age. Adults emerging from larval collections in the same villages were tested against the same insecticides at 3–5, 8–11 or 17–20 days old.
Findings
Mosquitoes collected nearest to the aquatic habitats (50-100 m) had the lowest mortalities compared to other distances, with a maximum of 51% mortality at 10× permethrin. For the age-synchronized mosquitoes collected as larvae, the insecticide-induced mortality assessed at both the diagnostic and multiplicative doses (1×, 5× and 10×) increased with mosquito age. The highest mortalities at 1× doses were observed among the oldest mosquitoes (17–20 days). At 10× doses, mortalities were 99% (permethrin) and 76% (deltamethrin) among 8–11 day-olds compared to 80% (permethrin) and 58% (deltamethrin) among 3–5 day-olds. Pre-exposure to PBO increased the potency of both pyrethroids. The proportion of parous females was highest among mosquitoes collected farthest from the habitats.
Conclusion
In this specific setting, older
An. funestus
and those collected farthest from the aquatic habitats (near the centre of the village) were more susceptible to pyrethroids than the younger ones and those caught nearest to the habitats. These findings suggest that pyrethroid-based interventions may remain at least moderately effective despite widespread pyrethroid-resistance, by killing the older, less-resistant and potentially-infective mosquitoes. Further studies should investigate how and whether these observations could be exploited to optimize malaria control in different settings.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This article analyses the South African legal framework governing security rights in movable property with the view to inspire law reform. The analysis is based on a comparison of the current South ...African framework with the UNCITRAL Legislative Guide on Secured Transactions, a soft-law instrument containing international best practice. The problematic aspects of the South African framework benchmarked against the UNCITRAL Guide are: (1) not having a common legal framework that equally applies to all types of (including quasi-) real security transactions; (2) the scope of the current framework not being comprehensive (inclusive) enough; (3) not having an efficient enough method of creating the security right; (4) the current publicity method, particularly concerning special notarial bonds, being overly cumbersome and not providing effective public notice to third parties; and (5) the current enforcement measures potentially not being the most efficient. Regarding each of these problem areas, the article makes proposals on how the South African legislature could reform the current framework into one that is legally efficient and in step with international best practice.
Variability is a property shared by practically all active galactic nuclei (AGNs). This makes variability selection a possible technique for identifying AGNs. Given that variability selection makes ...no prior assumption about spectral properties, it is a powerful technique for detecting both low-luminosity AGNs in which the host galaxy emission is dominating and AGNs with unusual spectral properties. In this paper, we will discuss and test different statistical methods for the detection of variability in sparsely sampled data that allow full control over the false positive rates. We will apply these methods to the GOODS North and South fields and present a catalog of variable sources in the z band in both GOODS fields. Out of the 11,931 objects checked, we find 155 variable sources at a significance level of 99.9%, corresponding to about 1.3% of all objects. After rejection of stars and supernovae, 139 variability-selected AGNs remain. Their magnitudes reach down as faint as 25.5 mag in z. Spectroscopic redshifts are available for 22 of the variability-selected AGNs, ranging from 0.046 to 3.7. The absolute magnitudes in the rest-frame z band range from ~--18 to --24, reaching substantially fainter than the typical luminosities probed by traditional X-ray and spectroscopic AGN selection in these fields. Therefore, this is a powerful technique for future exploration of the evolution of the faint end of the AGN luminosity function up to high redshifts.
We present Hubble Space Telescope STIS FUV images of the Lyalpha and FUV continuum emission of the luminous emission-line nebulae in two cooling-core clusters, A1795 and A2597. The Lyalpha and FUV ...continuum emission consist of a diffuse component (approx60%) and more compact features (knots and filaments), which lie preferentially along the radio source edges. There are correlations between the FUV continuum flux and the emission-line fluxes of Lyalpha and Halpha that imply that the brighter parts of the nebulae are ionized locally. We suggest that the FUV knots are star clusters with ongoing star formation of several solar masses per year. The bolometric luminosity of such a starburst (if absorbed by dust) would be detectable with the Spitzer Space Telescope MIPS. It appears that star formation occurs throughout the nebula, although it is strongly enhanced along the edges of the radio source. We find that young hot stars (e.g. O5) probably provide the bulk of the photons that ionize the nebula, although other sources of ionization may contribute in selected regions of the nebula. Constraints on diagnostic UV emission lines are consistent with photoionization from a starburst population and perhaps marginally with intermediate-velocity shocks, approx400 km s super(-1). We suggest that the mass accretion rates are comparable to the star formation rates (of order 10 M sub(o) yr super(-1)). This is consistent with the lack of intermediate- temperature gas (<1 keV) being due to energy input to the cooling gas rather than to "hiding" the cooling gas.
KINEMATIC DOWNSIZING AT z ∼ 2 Simons, Raymond C.; Kassin, Susan A.; Trump, Jonathan R. ...
The Astrophysical journal,
10/2016, Letnik:
830, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT We present results from a survey of the internal kinematics of 49 star-forming galaxies at in the CANDELS fields with the Keck/MOSFIRE spectrograph, Survey in the near-Infrared of Galaxies ...with Multiple position Angles (SIGMA). Kinematics (rotation velocity Vrot and gas velocity dispersion ) are measured from nebular emission lines which trace the hot ionized gas surrounding star-forming regions. We find that by , massive star-forming galaxies ( ) have assembled primitive disks: their kinematics are dominated by rotation, they are consistent with a marginally stable disk model, and they form a Tully-Fisher relation. These massive galaxies have values of that are factors of 2-5 lower than local well-ordered galaxies at similar masses. Such results are consistent with findings by other studies. We find that low-mass galaxies ( ) at this epoch are still in the early stages of disk assembly: their kinematics are often dominated by gas velocity dispersion and they fall from the Tully-Fisher relation to significantly low values of Vrot. This "kinematic downsizing" implies that the process(es) responsible for disrupting disks at have a stronger effect and/or are more active in low-mass systems. In conclusion, we find that the period of rapid stellar mass growth at is coincident with the nascent assembly of low-mass disks and the assembly and settling of high-mass disks.
Abstract
We present the most distant detection of cosmic voids (
z
∼ 2.3) and the first detection of three-dimensional voids in the Ly
α
forest. We used a 3D tomographic map of the absorption with ...an effective comoving spatial resolution of 2.5
h
−1
Mpc and a volume of 3.15 × 10
5
h
−3
Mpc
3
, which was reconstructed from moderate-resolution Keck I/LRIS spectra of 240 background Lyman-break galaxies and quasars in a 0.16 deg
2
footprint in the COSMOS field. Voids were detected using a spherical overdensity finder calibrated from hydrodynamical simulations of the intergalactic medium (IGM). This allows us to identify voids in the IGM corresponding to voids in the underlying matter density field, yielding a consistent volume fraction of voids in both data (19.5%) and simulations (18.2%). We fit excursion set models to the void radius function and compare the radially averaged stacked profiles of large voids (
r
> 5
h
−1
Mpc) to stacked voids in mock observations and the simulated density field. Comparing with 432 coeval galaxies with spectroscopic redshifts in the same volume as the tomographic map, we find that the tomography-identified voids are underdense in galaxies by 5.95
σ
compared to random cells.
We present the results from the application of a two-dimensional emission line detection method, EMission-line two-Dimensional (EM2D), to the near-infrared G102 grism observations obtained with the ...Wide-Field Camera 3 (WFC3) as part of the Cycle 22 Hubble Space Telescope Treasury Program: the Faint Infrared Grism Survey (FIGS). Using the EM2D method, we have assembled a catalog of emission line galaxies (ELGs) with resolved star formation from each of the four FIGS fields. Not only can one better assess the global properties of ELGs, but the EM2D method allows for the analysis and improved study of the individual emission-line region within each galaxy. This paper includes a description of the methodology, advantages, and the first results of the EM2D method applied to ELGs in FIGS. The advantage of 2D emission line measurements includes significant improvement of galaxy redshift measurements, approaching the level of accuracy seen in high-spectral-resolution data, but with greater efficiency; and the ability to identify and measure the properties of multiple sites of star formation and over scales of ∼1 kpc within individual galaxies out to z ∼ 4. The EM2D method also significantly improves the reliability of high-redshift (z ∼ 7) Ly detections. Coupled with the wide field of view and high efficiency of space-based grism observations, EM2D provides a noteworthy improvement on the physical parameters that can be extracted from grism observations.
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