Radial migration is defined as the change in guiding centre radius of stars and gas caused by gains or losses of angular momentum that result from gravitational interaction with non-axisymmetric ...structure. This has been shown to have significant impact on the metallicity distribution in galactic discs, and therefore affects the interpretation of Galactic archaeology. We use a simulation of a Milky Way-sized galaxy to examine the effect of radial migration on the star and gas radial metallicity distribution. We find that both the star and gas component show significant radial migration. The stellar radial metallicity gradient remains almost unchanged but the radial metallicity distribution of the stars is broadened to produce a greater dispersion at all radii. However, the metallicity dispersion of the gas remains narrow. We find that the main drivers of the gas metallicity distribution evolution are metal enrichment and mixing: more efficient metal enrichment in the inner region maintains a negative slope in the radial metallicity distribution, and the metal mixing ensures the tight relationship of the gas metallicity with the radius. The metallicity distribution function reproduces the trend in the age-metallicity relation found from observations for stars younger than 1.0 Gyr in the Milky Way.
Radial distribution of stellar motions in Gaia DR2 Kawata, Daisuke; Baba, Junichi; Ciucă, Ioana ...
Monthly Notices of the Royal Astronomical Society Letters,
09/2018, Letnik:
479, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract By taking advantage of the superb measurements of position and velocity for an unprecedented large number of stars provided in Gaia DR2, we have generated the first maps of the rotation ...velocity, Vrot, and vertical velocity, Vz, distributions as a function of the Galactocentric radius, Rgal, across a radial range of 5 < Rgal < 12 kpc. In the R − Vrot map, we have identified many diagonal ridge features, which are compared with the location of the spiral arms and the expected outer Lindblad resonance of the Galactic bar. We have detected also radial wave-like oscillations of the peak of the vertical velocity distribution.
The first half of this paper explores the origin of systematic biases in the measurement of weak gravitational lensing. Compared to previous work, we expand the investigation of point spread function ...instability and fold in for the first time the effects of non-idealities in electronic imaging detectors and imperfect galaxy shape measurement algorithms. Together, these now explain the additive
and multiplicative
systematics typically reported in current lensing measurements. We find that overall performance is driven by a product of a telescope/camera's absolute performance, and our knowledge about its performance.
The second half of this paper propagates any residual shear measurement biases through to their effect on cosmological parameter constraints. Fully exploiting the statistical power of Stage IV weak lensing surveys will require additive biases
and multiplicative biases
. These can be allocated between individual budgets in hardware, calibration data and software, using results from the first half of the paper.
If instrumentation is stable and well calibrated, we find extant shear measurement software from Gravitational Lensing Accuracy Testing 2010 (GREAT10) already meet requirements on galaxies detected at signal-to-noise ratio = 40. Averaging over a population of galaxies with a realistic distribution of sizes, it also meets requirements for a 2D cosmic shear analysis from space. If used on fainter galaxies or for 3D cosmic shear tomography, existing algorithms would need calibration on simulations to avoid introducing bias at a level similar to the statistical error. Requirements on hardware and calibration data are discussed in more detail in a companion paper. Our analysis is intentionally general, but is specifically being used to drive the hardware and ground segment performance budget for the design of the European Space Agency's recently selected Euclid mission.
ABSTRACT
Using a numerical simulation of an isolated barred disc galaxy, we first demonstrate that the resonances of the inner bar structure induce more prominent features in the action space ...distribution for the kinematically hotter stars, which are less sensitive to the local perturbation, such as the transient spiral arms. Then, we analyse the action distribution for the kinematically hotter stars selected from the Gaia EDR3 data as the stars with higher values of radial and vertical actions. We find several resonance features, including two new features, in the angular momentum distribution similar to what are seen in our numerical simulations. We show that the bar pattern speeds of about Ωbar ∼ 34 and 42 km s−1 kpc−1 explain all these features equally well. The resonance features we find correspond to the inner 4:1, co-rotation (CR), outer 4:1, outer Lindblad, and outer 4:3 (CR, outer 4:1, outer Lindblad, outer 4:3, and outer 1:1) resonances, when Ωbar ∼ 34 (42) km s−1 kpc−1 is assumed.
Recent numerical N-body simulations of spiral galaxies have shown that spiral arms in N-body simulations do not rotate rigidly as expected in classic density wave theory, but instead seem to rotate ...at a similar speed to the local rotation speed of the stellar disc material. This in turn yields winding, transient and recurrent spiral structure, whose corotating nature gives rise to changes in the angular momentum (radial migration) of star particles close to the spiral arm at many radii. From high-resolution N-body simulations, we highlight the evolution of strongly migrating star particles (migrators) and star particles that do not migrate (non-migrators) around a spiral arm. We investigate the individual orbit histories of migrators and non-migrators and find that there are several types of migrator and non-migrator, each with unique radial evolution. We find the important quantities that affect the orbital evolution to be the radial and tangential velocity components in combination with the azimuthal distance to the spiral arm at the time the star particle begins to feel tangential force. We contrast each type of orbit to compare how these factors combine for migrators and non-migrators. We find that the positive (negative) migrators sustain a position behind (in front of) the spiral arm, and feel continuous tangential force as long as the spiral arm persists. This is because the positive (negative) migrators are close to the apocentre (pericentre) epicycle phase during their migration, and rotate slower (faster) than the corotating spiral arm. On the other hand, non-migrators stay close to the spiral arm, and pass or are passed by the spiral arm one or two times. Although they gain or lose the angular momentum when they are behind or in front of the spiral arm, their net angular momentum change becomes close to zero. We discuss also the long-term effects of radial migration on the radial metallicity distribution and radial angular momentum and mass profiles.
Fuel cells: a survey of current developments Cropper, Mark A.J; Geiger, Stefan; Jollie, David M
Journal of power sources,
05/2004, Letnik:
131, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
Since the first practical uses of fuel cells were developed, it has become clear that they could find use in many products over a wide power range of milliwatts to tens of megawatts. Throughout the ...1990s, and later, there has been significant work carried out on adapting the various different fuel cell technologies for use in targetted consumer and industrial applications. This paper discusses these developments and gives details on the specific market segments for providing power to vehicles, portable devices and large- and small-scale stationary power generation.
We have observed a snapshot of our N-body/smoothed particle hydrodynamics simulation of a Milky Way-sized barred spiral galaxy in a similar way to how we can observe the Milky Way. The simulated ...galaxy shows a corotating spiral arm, i.e. the spiral arm rotates with the same speed as the circular speed. We observed the rotation and radial velocities of the gas and stars as a function of the distance from our assumed location of the observer at the three lines of sight on the disc plane, (l, b) = (90, 0), (120, 0) and (150, 0) deg. We find that the stars tend to rotate slower (faster) behind (at the front of) the spiral arm and move outwards (inwards), because of the radial migration. However, because of their epicycle motion, we see a variation of rotation and radial velocities around the spiral arm. On the other hand, the cold gas component shows a clearer trend of rotating slower (faster) and moving outwards (inwards) behind (at the front of) the spiral arm, because of the radial migration. We have compared the results with the velocity of the maser sources from Reid et al., and find that the observational data show a similar trend in the rotation velocity around the expected position of the spiral arm at l = 120 deg. We also compared the distribution of the radial velocity from the local standard of the rest, V
LSR, with the Apache Point Observatory Galactic Evolution Experiment (APOGEE) data at l = 90 deg as an example.
We combine near-ultraviolet (NUV), optical and IR imaging of the nearby starburst galaxy M82 to explore the properties of the dust both in the interstellar medium of the galaxy and the dust entrained ...in the superwind. The three NUV filters of Swift-Ultraviolet/Optical Telescope enable us to probe in detail the properties of the extinction curve in the region around the 2175 Å bump. The NUV colour-colour diagram strongly rules out a 'bump-less' Calzetti-type law, which can either reflect intrinsic changes in the dust properties or in the star formation history compared to starbursts well represented by such an attenuation law. We emphasize that it is mainly in the NUV region where a standard Milky Way-type law is preferred over the Calzetti law. The age and dust distribution of the stellar populations is consistent with the scenario of an encounter with M81 in the recent 400 Myr. The radial variation of NUV/optical/IR photometry in the galaxy region - including the polycyclic-aromatic-hydrocarbon-dominated emission at 8 μm - confirms the central location of the star formation. The radial gradients of the NUV and optical colours in the superwind region supports the hypothesis that the emission in the wind cone is driven by scattering from dust grains entrained in the ejecta. The observed wavelength dependence, ∝λ−1.5, reveals either a grain size distribution n(a) ∝ a
−2.5, or a flatter distribution with a maximum size cutoff, suggesting that only small grains are entrained in the supernova-driven wind.
We have observed an N-body/smoothed particle hydrodynamics simulation of a Milky Way-like barred spiral galaxy. We present a simple method that samples N-body model particles into mock Gaia stellar ...observations and takes into account stellar populations, dust extinction and Gaia’s science performance estimates. We examine the kinematics of stars with V ≤ 16 mag around a nearby spiral arm at a similar position to the Perseus arm at three lines of sight in the disc plane; (l, b) = (90, 0), (120, 0) and (150, 0) deg. We find that the structure of the peculiar kinematics around the corotating spiral arm, which is found in Kawata et al. (2014b), is still visible in the observational data expected to be produced by Gaia, despite the dust extinction and expected observational errors of Gaia. These observable kinematic signatures will enable testing whether the Perseus arm of the Milky Way is similar to the corotating spiral arms commonly seen in N-body simulations.
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