East-west Features Research Articles

Evidence for a jet and outflow from Sgr A*: a continuum and spectral line study

ABSTRACT We study the environment of Sgr A* using spectral and continuum observations with the Atacama Large Millimeter/submillimeter Array and Very Large Array. Our analysis of subarcsecond H30 α, H39 α, H52 α , and H56 α line emission towards Sgr A* confirms the recently published broad-peak ∼500 km s−1 spectrum towards Sgr A*. We also detect emission at more extreme radial velocities peaking near −2500 and 4000 km s−1 within 0.2 arcsec. We then present broad-band radio continuum images at multiple frequencies on scales from arcseconds to arcminutes. A number of elongated continuum structures lie parallel to the Galactic plane, extending from ∼0.4 arcsec to ∼10 arcmin. We note a non-thermal elongated structure on an arcminute scale emanating from Sgr A* at low frequencies between 1 and 1.4 GHz where thermal emission from the minispiral is depressed by optical depth effects. The position angle of this elongated structure and the sense of motion of ionized features with respect to Sgr A* suggest a symmetric, collimated jet emerging from Sgr A* with an opening angle of ∼30○ and a position angle of ∼60○ punching through the medium before accelerating a significant fraction of the orbiting ionized gas to high velocities. The jet with an estimated mass flow rate of ∼1.4 × 10−5 M⊙ yr−1 emerges perpendicular to the equatorial plane of the accretion flow near the event horizon of Sgr A* and runs along the Galactic plane. To explain a number of east–west features near Sgr A*, we also consider the possibility of an outflow component with a wider angle launched from the accretion flow at larger radii.

Near- and Mid-infrared Observations in the Inner Tenth of a Parsec of the Galactic Center Detection of Proper Motion of a Filament Very Close to Sgr A*

Abstract We analyze the gas and dust emission in the immediate vicinity of the supermassive black hole Sgr A* at the Galactic center (GC) with the ESO Very Large Telescope (Paranal/Chile) instruments SINFONI and VISIR. The SINFONI H+K data cubes show several emission lines with related line map counterparts. From these lines, the Brγ emission is the most prominent one and appears to be shaped as a bar extending along the north–south direction. With VISIR, we find a dusty counterpart to this filamentary emission. In this work, we present evidence that this feature could most be likely connected to the minispiral and potentially influenced by the winds of the massive stars in the central cluster or an accretion wind from Sgr A*. To this end, we coadd the SINFONI data between 2005 and 2015. The spectroscopic analysis reveals a range of Doppler-shifted emission lines. We also detect substructures in the shape of clumps that can be investigated in the channel maps of the Brγ bar. In addition, we compare the detection of the near-infrared Brγ feature to PAH1 mid-infrared observations and published 226 GHz radio data. These clumps show a proper motion of about 320 km s−1 that are consistent with other infrared continuum–detected filaments in the GC. Deriving a mass of for the investigated Brγ feature shows an agreement with former derived masses for similar objects. Besides the north–south Brγ bar, we find a comparable additional east–west feature. Also, we identify several gas reservoirs that are located west of Sgr A* that may harbor dusty objects.

Examining the geometry, age and genesis of buried Quaternary valley systems in the Midland Valley of Scotland, UK

Buried palaeo‐valley systems have been identified widely beneath lowland parts of the UK including eastern England, central England, south Wales and the North Sea. In the Midland Valley of Scotland palaeo‐valleys have been identified yet the age and genesis of these enigmatic features remain poorly understood. This study utilizes a digital data set of over 100 000 boreholes that penetrate the full thickness of deposits in the Midland Valley of Scotland. It identified 18 buried palaeo‐valleys, which range from 4 to 36 km in length and 24 to 162 m in depth. Geometric analysis has revealed four distinct valley morphologies, which were formed by different subglacial and subaerial processes. Some palaeo‐valleys cross‐cut each other with the deepest features aligning east–west. These east–west features align with the reconstructed ice‐flow direction under maximum conditions of the Main Late Devensian glaciation. The shallower features appear more aligned to ice‐flow direction during ice‐sheet retreat, and were therefore probably incised under more restricted ice‐sheet configurations. The bedrock lithology influences and enhances the position and depth of palaeo‐valleys in this lowland glacial terrain. Faults have juxtaposed Palaeozoic sedimentary and igneous rocks and the deepest palaeo‐valleys occur immediately down‐ice of knick‐points in the more resistant igneous bedrock. The features are regularly reused and the fills are dominated by glacial fluvial and glacial marine deposits. This suggests that the majority of infilling of the features happened during deglaciation and may be unrelated to the processes that cut them.

Hydrochemical Analysis of Ground‐Water Flow and Saline Incursion in the Clarendon Basin, Jamaica

AbstractThe Clarendon Basin of south‐central Jamaica has been recognized for its productive sugar cane industry since the late 1800s. Much of its success is attributed to rich alluvial soils, a year‐round tropical climate and copious supplies of good quality irrigation water from a karstic limestone aquifer of Tertiary age. This aquifer extends throughout the northern part of the basin, but ends abruptly at the South Coast Fault, an east west feature that forms the northern boundary of a deep graben filled with alluvial sediments. These alluvial sediments are the only source of water for the area south of the fault (the Vere Plain). However, the sediments also lap onto the limestone to the north of the fault (the Clarendon Plain) and provide a supplementary ground‐water source. By the early 1970s nearly 200 wells supplied irrigation water for over 20,000 hectares of land. As development increased, the salinity of the ground water increased. Consequently, many wells were closed down and several sugar plantations were abandoned. In the study presented here, major ion (Ca, Mg, Na, K, HCO3, Cl, SO4, and NO3), minor ion (F, Br, and I), and environmental isotope (δ18O,δD) hydrochemistry is used to resolve the hydrodynamics of ground‐water flow in the basin and identify the source and mode of emplacement of the saline water.Oxygen and hydrogen isotope data confirm that while the major well production areas are located in lowland coastal areas, recharge originates almost exclusively as rainfall in the cooler elevated parts of the basin above 750 m (asl). Subsurface conduit flow brings this water to the limestone well fields, and any excess water is able to cross the South Coast Fault to feed the alluvial aquifer of the Vere Plain. The thin alluvial aquifer of the Clarendon Plain also receives limestone water but this water does not enter entirely by subsurface means. Instead data suggest that while some of the water can be attributed to natural upward vertical leakage in the northwest of the Clarendon Plain, the remainder can be attributed to the seepage of irrigation water drawn, at least in part, from wells developed in the underlying limestone.Saline ground waters affect all the aquifers of the basin and several potential sources have been proposed. Major and minor ion data point to a sea‐water source, and a sea‐water wedge extending beneath the thick alluvial aquifer of the Vere Plain is an obvious candidate for the source of salinity observed in wells from this aquifer. Closer examination of the chemical data reveals, however, that wells in the limestone and alluvial aquifers to the north of the South Coast Fault do not derive their salinity from this source location, and instead draw sea water from the east and west along the relatively permeable South Coast Fault zone. This water can move to limestone wells directly; wells in the alluvium of the Clarendon Plain, however, receive most of the saline water indirectly via leakage of irrigation water pumped initially from the limestone. Sea water drawn along the fault may also be the primary source of salinity in the aquifer of the Vere Plain but this cannot be confirmed on the basis of hydrochemical evidence alone.

Deformation of the Archean Quetico–Shebandowan subprovince boundary in the Canadian Shield near Kashabowie, northern Ontario

The southern boundary of the Quetico metasedimentary subprovince of the Superior Province of the Canadian Shield near Kashabowie, Ontario, is a vertical, east–west feature affected by dextral transpression that had a north-northwest – south-southeast compressional component. A synmetamorphic, locally D1 microfabric and magnetic-susceptibility fabric with an east-directed extension lineation is kinematically compatible with this pattern. It shows the same bedding–cleavage relationship and the same direction of structural facing on D1 in both the Quetico metasediments and the Shebandowan greenstone subprovince on the south side of the Quetico subprovince. In the low-grade rocks of the study area, there is a single phase of penetrative deformation, giving a nearly vertical schistosity at a consistent angle, anticlockwise with respect to the now nearly vertical east–west-striking strata. The absence of penetrative polyphase deformations may be due to the near parallelism of the subprovince boundary with the shear component of dextral transpression. Strain analysis indicates that the minimum shortening of the greywackes is 40% in a north–south direction. It is tentatively suggested that the shortening, the steepening of strata into a vertical position, and some of the S1 fabric development may have occurred prior to the climax of metamorphism and transpression. If this sequence is correct, the strata would have dipped gently to the north prior to the steepening event, with the embryonic schistosity dipping to the west.

The stratigraphy and structure of the Galley Head culmination zone: An area of enhanced shortening related to basin geometry within the Irish Variscides

AbstractIn southwest Ireland an Upper Devonian to Lower Carboniferous clastic succession was deposited in an ENE–WSW trending half‐graben, known as the South Munster Basin. Across the Galley Head peninsula on the south coast, this stratigraphical succession is attenuated due to the presence of a palaeogeographical feature called the Glandore High. Evidence suggests that the Glandore High was an east–west feature, faulted to the north and east, which was part of the southern flank (hangingwall rollover) of the South Munster Basin.During post‐Carboniferous Variscan deformation the relatively thin stratigraphy of Galley Head underwent prolonged folding, causing a local periclinal fold pair to develop within the hinge zone of a regional syncline. The main cleavage then developed parallel to bedding on the overturned south limb of the anticline of this fold pair. The local enhanced shortening caused the development of a structural culmination, and south facing, tight to isoclinal folds. The culmination was enhanced and tightened by a fault system of contractional, strike‐parallel faults linked by cross faults. Secondary folds occur across the hinges of regional anticlines and also on major fold limbs as isolated fold pairs and in monoclinal fold zones, some of which may have nucleated on irregular sandstone bodies. Local crenulation cleavages are related to late fault movements. Syn‐cleavage, conjugate, wrench faults record 10 per cent to 15 per cent strike‐parallel extension in the culmination.The deformation chronology of the Galley Head area is somewhat anomalous for the Irish Variscides in that the folds were well established before the onset of the main cleavage development. The enhanced shortening across the area was compartmentalized by major cross faults and a minor component of north–south sinistral shear was also active across the area causing a swing in strike and a late set of minor cross faults.Structural facing directions in southwest Ireland appear to be directly linked with the geometry of the deformed basins. Hence the southward facing along the south coast is due to the proximity of the southern margin of the South Munster Basin. Structural facing directions fan northwards across the basin and major folds are overturned to the north at the northern margin of the basin.

Coherent Fluctuations of Fxtratropical Geopotential Height and Tropical Convection in Intraseasonal Time Scales

Northern-Hemisphere twice-daily 500-mb-geopotential-height data for November-March 1975-1980 and November-December 1981 and NOAA satellite measurements of outgoing longwave radiation for the same period are processed to remove seasonal cycles and Fourier-decomposition bandpassed to study variations with 20-70-d periods. The results of analysis using correlation, complex EOF, and composite techniques are presented in extensive maps and graphs and characterized. Extratropical wavetrains are found to evolve systematically from Eurasia eastward to North America and the North Atlantic on 5-6-d time scales, while the intraseasonal variation in tropical convection is dominated by a dipolelike east-west feature propagating from the western Indian Ocean to the dateline with a quasi-period of 40-50 d. The possibility that normal modes coupled between the tropics and midlatitudes may be responsible for these phenomena is considered.

The Amazon shearing system

Abstract In the Amazon region there is a trough-like east-west feature hidden by young sediments. In the trough itself, which is transversely split up, there are Palaeozoic strata which have survived because of the subsidence. This probably took place when the Gondwana continent broke up whereby basaltics intruded. These are attributed to the Jurassic period although they are normally found as sills in the Palaeozoic sediments of the Amazon region. In addition, the Amazon Graben exhibits dislocation by a transcurrent fault system such that the northern block (= Guayana Shield) is transposed considerably to the west when compared with the southern block (Brazilian Shield). The Amazon transcurrent fault is a left-handed shearing system. Relations between the Amazon shearing system and the West African Benoue Graben, between the sigmoidal bulge of the western South American shore line and the West African continental margin and the proximity of the equator are discussed.

The musgrave mountain belt in South Australia

Structural elements impressed upon the more easterly extensions of the Westralian shield were dominantly east-west features. These tendencies have channelled subsequent orogenies and geomorphic evolution, right down through the long history of the area.