Intense, millisecond-duration bursts of radio waves (named fast radio bursts) have been detected from beyond the Milky Way
. Their dispersion measures-which are greater than would be expected if they ...had propagated only through the interstellar medium of the Milky Way-indicate extragalactic origins and imply contributions from the intergalactic medium and perhaps from other galaxies
. Although several theories exist regarding the sources of these fast radio bursts, their intensities, durations and temporal structures suggest coherent emission from highly magnetized plasma
. Two of these bursts have been observed to repeat
, and one repeater (FRB 121102) has been localized to the largest star-forming region of a dwarf galaxy at a cosmological redshift of 0.19 (refs.
). However, the host galaxies and distances of the hitherto non-repeating fast radio bursts are yet to be identified. Unlike repeating sources, these events must be observed with an interferometer that has sufficient spatial resolution for arcsecond localization at the time of discovery. Here we report the localization of a fast radio burst (FRB 190523) to a few-arcsecond region containing a single massive galaxy at a redshift of 0.66. This galaxy is different from the host of FRB 121102, as it is a thousand times more massive, with a specific star-formation rate (the star-formation rate divided by the mass) a hundred times smaller.
ABSTRACT
The Deep Synoptic Array 10-dish prototype (DSA-10) is an instrument designed to detect and localize fast radio bursts with arcsecond accuracy in real time. Deployed at Owens Valley Radio ...Observatory, it consists of ten 4.5-m diameter dishes, equipped with a 250-MHz bandwidth dual polarization receiver, centred at 1.4 GHz. The 20 input signals are digitized and field programmable gate arrays are used to transform the data to the frequency domain and transmit it over ethernet. A series of computer servers buffer both raw data samples and perform a real time search for fast radio bursts on the incoherent sum of all inputs. If a pulse is detected, the raw data surrounding the pulse are written to disc for coherent processing and imaging. The prototype system was operational from 2017 June to 2018 February conducting a drift scan search. Giant pulses from the Crab Pulsar were used to test the detection and imaging pipelines. The 10-dish prototype system was brought online again in 2019 March, and will gradually be replaced with the new DSA-110, a 110-dish system, over the next 2 yr to improve sensitivity and localization accuracy.
Using CARMA, we imaged the 87 GHz SiO v = 0 J = 2-1 line toward Orion-KL with 0.''45 angular resolution. The maps indicate that radio source I drives a bipolar outflow into the surrounding molecular ...cloud along a NE-SW axis, in agreement with the model of Greenhill et al. The extended high-velocity outflow from Orion-KL appears to be a continuation of this compact outflow. High-velocity gas extends farthest along a NW-SE axis, suggesting that the outflow direction changes on timescales of a few hundred years.
Abstract
Ten years ago, the genus-level and species-level taxonomy of African pipistrelloid bats was in a state of flux. In spite of advances in the past decade, gaps in collecting from species-rich ...regions like Angola have hampered efforts to revise this group. We report on new collections of pipistrelle-like bats from the poorly sampled central highlands of Angola (1000–1500 m a.s.l.) as well as comparative material from lower-lying areas of Eswatini and South Africa. Specimens identified as Neoromicia anchietae, collected 400–700 km east of the holotype locality in the western highlands of Angola, were genetically and morphologically distinctive from N. anchietae s.l. from South Africa and Eswatini. We describe herein this latter lineage as a distinct species from low-lying areas of south-eastern Africa, distinct from N. anchietae s.s., which is therefore restricted to the central and western Angolan highlands. We also identified shallow to deep genetic divergence between different African regions in other recognized pipistrelloid species, such as conspecificity between the long-eared species Laephotis angolensis from Angola and Laephotis botswanae from northern Botswana, northern Namibia and south-western Zambia. Our phylogeny supports a recently proposed generic classification of African pipistrelloid bats.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We respond to recent criticisms of supposed “taxonomic anarchy” which is said to hamper conservation efforts. Using examples from African small mammals, we document recent increases of 13% (rodents) ...and 18% (bats) over the past three decades in the number of recognized species of Afro-Malagasy rodents and bats. By reference to a number of case studies involving Afro-Malagasy taxa (predominantly from montane habitats), and a suggested four-criterion approach to delimiting species accurately, we show that these increases are a genuine reflection of speciation in cryptic species complexes. Moreover, we show that some of these cryptic species are subject to increased extinction risks due to small population size and anthropogenic changes (habitat degradation and climate change). These changes were captured accurately in a recent Mammal Red List of South Africa, Lesotho and Swaziland, indicating that taxonomists and conservationists can work together to assess the Red List status of cryptic species based on robust taxonomic revisions.
The 229 GHz (lambda 1.3 mm) radio emission from Orion-KL was mapped with up to 0".4 angular resolution with CARMA, allowing measurements of the flux densities of Source I ("SrcI") and the ...Becklin-Neugebauer Object (BN), the two most massive stars in this region. We find integrated flux densities of 310 + or - 45 mJy for SrcI and 240 + or - 35 mJy for BN. SrcI is optically thick even at 229 GHz. No trace of the H30 alpha recombination line is seen in its spectrum, although the nu sub(2) = 1, 5(5,0)-6(4,3) transition of H sub(2)O, 3450 K above the ground state, is prominent. SrcI is elongated at position angle 140degrees, as in 43 GHz images. These results are most easily reconciled with models in which the radio emission from SrcI arises via the H- free-free opacity in a T < 4500 K disk, as considered by Reid et al. By contrast, the radio spectrum of BN is consistent with p super(+)/e super(-) free-free emission from a dense (ne ~ 5 x 10 super(7) cm super(-3)), but otherwise conventional, hypercompact H II region. The source is becoming optically thin at 229 GHz, and the H30 alpha recombination line, at V sub(LSR) = 23.2 + or - 0.5 km s super(-1), is prominent in its spectrum. A Lyman continuum flux of 5 x 10 super(45) photons s super(-1), consistent with that expected from a B star, is required to maintain the ionization. Supplementary 90 GHz observations were made to measure the H41 alpha and H42 alpha recombination lines toward BN. Published 43 and 86 GHz data suggest that SrcI brightened with respect to BN over the 15 year period from 1994 to 2009.
South-central Africa is characterized by an archipelago of wetlands, which has evolved in time and space since at least the Miocene, providing refugia for animal species during Pleistocene arid ...episodes. Their importance for biodiversity in the region is reflected in the evolution of a variety of specialist mammal and bird species, adapted to exploit these wetland habitats. Populations of lions (Panthera leo) across south-central and east Africa have contrasting signatures of mitochondrial DNA haplotypes and biparental nuclear DNA in wetland and savannah habitats, respectively, pointing to the evolution of distinct habitat preferences. This explains the absence of genetic admixture of populations from the Kalahari savannah of southwest Botswana and the Okavango wetland of northern Botswana, despite separation by only 500 km. We postulate that ancestral lions were wetland specialists and that the savannah lions evolved from populations that were isolated during arid Pleistocene episodes. Expansion of grasslands and the resultant increase in herbivore populations during mesic Pleistocene climatic episodes provided the stimulus for the rapid population expansion and diversification of the highly successful savannah lion specialists. Our model has important implications for lion conservation.
ABSTRACT We present a 67-93.6 GHz spectral line survey of Orion-KL with the new 4 mm Receiver on the Green Bank Telescope (GBT). The survey reaches unprecedented depths and covers the low-frequency ...end of the 3 mm atmospheric window which has been relatively unexplored previously. The entire spectral-line survey is published electronically for general use by the astronomical community. The calibration and performance of the 4 mm Receiver on the GBT is also summarized.
We tested the prediction that at coarse spatial scales, variables associated with climate, energy, and productivity hy- potheses should be better predictor（s） of bat species richness than those ...associated with environmental heterogeneity. Distribution ranges of 64 bat species were estimated with niche-based models informed by 3629 verified museum specimens. The influence of environmental correlates on bat richness was assessed using ordinary least squares regression （OLS）, simultaneous autoregressive models （SAR）, conditional autoregressive models （CAR）, spatial eigenvector-based filtering models （SEVM）, and Classification and Regression Trees （CART）. To test the assumption of stationarity, Geographically Weighted Regression （GWR） was used. Bat species richness was highest in the eastern parts of southern Africa, particularly in central Zimbabwe and along the western border of Mozambique. We found support for the predictions of both the habitat heterogeneity and climate/productivity/energy hypothe- ses, and as we expected, support varied among bat families and model selection. Richness patterns and predictors of Miniopteridae and Pteropodidae clearly differed from those of other bat families. Altitude range was the only independent variable that was sig- nificant in all models and it was most often the best predictor of bat richness. Standard coefficients of SAR and CAR models were similar to those of OLS models, while those of SEVM models differed. Although GWR indicated that the assumption of stationa- rity was violated, the CART analysis corroborated the findings of the curve-fitting models. Our results identify where additional data on current species ranges, and future conservation action and ecological work are needed.
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