ALBERT

Description: Suppressing star formation in quiescent galaxies with supermassive black hole winds Nature 533, 7604 (2016). doi:10.1038/nature18006 Authors: Edmond Cheung, Kevin Bundy, Michele Cappellari, Sébastien Peirani, Wiphu Rujopakarn, Kyle Westfall, Renbin Yan, Matthew Bershady, Jenny E. Greene, Timothy M. Heckman, Niv Drory, David R. Law, Karen L. Masters, Daniel Thomas, David A. Wake, Anne-Marie Weijmans, Kate Rubin, Francesco Belfiore, Benedetta Vulcani, Yan-mei Chen, Kai Zhang, Joseph D. Gelfand, Dmitry Bizyaev, A. Roman-Lopes & Donald P. Schneider Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 1010 times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1, 2, 3, 4). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss or mergers and that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the quiescent population with masses around 2 × 1010 times that of the Sun. In a prototypical example, we calculate that the energy input from the galaxy’s low-level active supermassive black hole is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.

Description: A direct localization of a fast radio burst and its host Nature 541, 7635 (2017). doi:10.1038/nature20797 Authors: S. Chatterjee, C. J. Law, R. S. Wharton, S. Burke-Spolaor, J. W. T. Hessels, G. C. Bower, J. M. Cordes, S. P. Tendulkar, C. G. Bassa, P. Demorest, B. J. Butler, A. Seymour, P. Scholz, M. W. Abruzzo, S. Bogdanov, V. M. Kaspi, A. Keimpema, T. J. W. Lazio, B. Marcote, M. A. McLaughlin, Z. Paragi, S. M. Ransom, M. Rupen, L. G. Spitler & H. J. van Langevelde Fast radio bursts are astronomical radio flashes of unknown physical nature with durations of milliseconds. Their dispersive arrival times suggest an extragalactic origin and imply radio luminosities that are orders of magnitude larger than those of all known short-duration radio transients. So far all fast radio bursts have been detected with large single-dish telescopes with arcminute localizations, and attempts to identify their counterparts (source or host galaxy) have relied on the contemporaneous variability of field sources or the presence of peculiar field stars or galaxies. These attempts have not resulted in an unambiguous association with a host or multi-wavelength counterpart. Here we report the subarcsecond localization of the fast radio burst FRB 121102, the only known repeating burst source, using high-time-resolution radio interferometric observations that directly image the bursts. Our precise localization reveals that FRB 121102 originates within 100 milliarcseconds of a faint 180-microJansky persistent radio source with a continuum spectrum that is consistent with non-thermal emission, and a faint (twenty-fifth magnitude) optical counterpart. The flux density of the persistent radio source varies by around ten per cent on day timescales, and very long baseline radio interferometry yields an angular size of less than 1.7 milliarcseconds. Our observations are inconsistent with the fast radio burst having a Galactic origin or its source being located within a prominent star-forming galaxy. Instead, the source appears to be co-located with a low-luminosity active galactic nucleus or a previously unknown type of extragalactic source. Localization and identification of a host or counterpart has been essential to understanding the origins and physics of other kinds of transient events, including gamma-ray bursts and tidal disruption events. However, if other fast radio bursts have similarly faint radio and optical counterparts, our findings imply that direct subarcsecond localizations may be the only way to provide reliable associations.

Description: One of the most outstanding apparent examples in N America of a forcibly emplaced pluton is the Papoose Flat Pluton of eastern California. Sideways expansion of this granitic pluton, during emplacement into a series of Cambrian shelf strata, has been regarded by early workers as resulting in the observed intense crystal plastic deformation of the pluton's mylonitic border facies and surrounding country rocks. This deformation is evidenced by up to 90% thinning of individual stratigraphic layers within the pluton's metamorphic aureole, although such intense penetrative deformation of the country rocks is not observed outside the aureole.Previously published quartz c-axis fabrics associated with this deformation (and presented on projection planes oriented perpendicular to lineation) were interpreted as being symmetrical with respect to foliation and lineation, implying almost coaxial deformation histories. Such fabrics could be interpreted as indicating that the pluton evolved by “ballooning” as a result of new magma being intruded into its core during emplacement. However, a major problem with applying the strict ballooning model to the Papoose Flat Pluton is that while oblate strains would be expected to develop in association with a ballooning mechanism, the mylonitic rocks of this elongate WNW-ESE-trending pluton and its aureole are characterised by both a strongly developed foliation, which is concordant with the pluton's margin, and an intense, NW-SE trending, shallow plunging stretching lineation.Previously published fabrics from the Papoose Flat Pluton and its metamorphic aureole have been rotated on to a projection plane oriented parallel to lineation and perpendicular to foliation. Examination of the fabrics in this projection plane has revealed that they are in fact dominantly asymmetric, and that a constant sense of asymmetry is detected across the pluton, suggesting a consistent (top-to-the-SE) shear-sense. This new interpretation is strongly supported by microstructural and petrofabric analysis of additional L-S tectonites collected, during recent fieldwork, from both the aureole and quartz veins within the pluton's gneissic border facies. Thus mylonite formation around the Papoose Flat Pluton could have involved large-scale consistently oriented translation and associated shearing, rather than passive “blister-like” coaxial deformation associated with pluton ballooning. It should be noted that mylonitic deformation is restricted to the western half of the pluton, features indicative of a more “permitted” emplacement mechanism being found in the eastern portion of the pluton.The detected top-to-the-SE shear-sense could be interpreted as indicating that the granitic material forming the western part of the pluton was forcibly intruded in a northwestward direction from the pluton source as a nearly solidified wedge beneath a static cover of sedimentary rocks. Alternatively, the detected shear sense could also be interpreted as indicating SE-directed thrusting of the cover rocks over the underlying pluton, the western margin of the pluton suffering intense mylonitic deformation, while the eastern margin was located in a “stress-shadow” region. If this alternative interpretation is correct, then the deformation temperatures indicated by the pattern of quartz c-axis fabrics dictate that thrusting must either be synchronous with pluton emplacement, or at least have commenced during the early stages of pluton cooling.

Description: summaryIn the Highlands of Kenya every 1-week delay in planting maize after the onset of the rains reduces the grain yield by approximately 0·6 t/ha. No satisfactory explanation has been found for this phenomenon. A physiological growth study was made on four dates of planting per year over 4 years. Early growth rates and maximum crop growth rates showed a progressive decline with delay in planting which resulted in smaller plants at 5 weeks post-emergence and at 50 % tassel emergence in maize planted later. There was a strong relationship between the size of plant at tasselling and the final grain yield and a highly significant relationship (r = 0·94) between the size of plant at 5 weeks post emergence and the final grain yield. Other environmental studies showed that soil temperature at 7·5 cm, coupled with a soil moisture stress factor, largely controlled the dry-matter production rate during early growth, and consideration of the mean value of these two variables over the first 5 weeks of growth accounted for 70% of the variation of dry matter at 5 weeks post-emergence. It was further shown that 82% of the variation in final grain yield caused by date of planting could be accounted for by consideration of the mean value of these two variables during the first 5 weeks of growth.

Description: SummaryPrevious work has shown a strong relationship between the mean soil temperature during the first 5 weeks of growth of a maize crop, and the final grain yield, warmer soils leading to greater yields. Trials were laid down in 1975 and 1976 to establish how early in the development of a maize crop higher soil temperatures would lead to increased yields. Soil temperatures were raised by polythene mulching applied at planting with six times of mulch removal: at crop emergence, 1, 2, 3, 4 and 5 weeks after emergence. Raised soil temperature led to a greater rate of development and leaf area production during early growth. Greater leaf area was due to greater leaf emergence rate rather than increase in leaf size, since increase in soil temperature was associated with a decrease in individual leaf size. This trend was reversed from leaf number 15 onwards resulting in no differences in leaf area, leaf weight or total dry matter at tasselling. In spite of this, yield differences were observed. Increase in soil temperature during germination alone had a beneficial effect on final grain yield, and this effect increased with duration. Increasing soil temperature for longer than 3–4 weeks from emergence caused no further yield increase. Yields increased from 133 and 172 g/ plant to 220 and 238 g/plant in 1975 and 1976 respectively. Yield increases were associated with more grains per plant rather than greater grain size. The period during which increased soil temperature led to increased yields coincided with the period when the apical meristem was below ground level. The mechanism involved is not yet clear.

Description: Early petrofabric studies of quartz c axis preferred orientation within the Tarskavaig Nappe, located at the southern end of the Moine thrust zone, have been interpreted as indicating that structures within the nappe have been produced by tectonic movements acting at right angles to those responsible for formation of structures within the overlying, but immediately adjacent, Moine Nappe. Such a dramatic contrast in inferred transport direction has not been recognized within the rest of the thrust zone.Re-examination of the microstructures and c axis fabrics within mylonitic metasediments from the western part of the Tarskavaig Nappe has revealed that these tectonites are characterized by maximum principal extension axes which trend sub-parallel to the WNW-trending Moine thrust zone transport direction. Later folding has reorientated and modified these structures within the eastern part of the nappe producing fabrics which have erroneously been taken to indicate a transport direction orientated sub-perpendicular to that of the rest of the Moine thrust zone.WNW-trending maximum principal extension axes and WNW-directed overthrust senses are indicated by microstructures within schists from the adjacent Moine Nappe, suggesting that structures within both the Tarskavaig and Moine nappes may be associated with a common west-northwest transport direction.Essentially coaxial (pure shear) strain paths (indicated by symmetrical c axis fabrics) dominate the internal parts of the Tarskavaig Nappe. Close to the base of the nappe, non-coaxial strain paths, originally associated with WNW-directed overthrusting, are indicated by asymmetrical c axis fabrics and oblique grain shape alignments. Strain compatibility considerations indicate that the lower kinematic domain (which must either be contemporaneous with, or later than, formation of the upper domain) must be characterized by a combination of pure and simple shear deformation.