Mass selection bias in galaxy cluster peculiar velocities from the kinetic Sunyaev–Zel'dovich effect     

Alan C. Peel 《Monthly notices of the Royal Astronomical Society》2006,365(4):1191-1202

Upcoming surveys for galaxy clusters using the Sunyaev–Zel'dovich effect are potentially sensitive enough to create a peculiar velocity catalogue. The statistics of these peculiar velocities are sensitive to cosmological parameters. We develop a method to explore parameter space using N -body simulations in order to quantify dark matter halo velocity statistics which will be useful for cluster peculiar velocity observations. We show that mass selection bias from a kinetic Sunyaev–Zel'dovich velocity catalogue forecasts rms peculiar velocities with a much more complicated  Ω_m  dependency than suggested by linear perturbation theory. In addition, we show that both two-point functions for velocities disagree with linear theory predictions out to  ∼40  h ⁻¹ Mpc  separations. A pedagogical appendix is included developing linear theory notation with respect to the two-point peculiar velocities functions.  相似文献   

Dual chromospheric flows in the vicinity of a solar pore     

U. M. Leiko  N. N. Kondrashova 《Kinematics and Physics of Celestial Bodies》2017,33(3):111-121

Chromospheric line-of-sight velocities are investigated in a small pore and its vicinity on the part of the active region NOAA 11024 with a size of 5″. We used H_α spectra of the active region and undisturbed atmosphere obtained with the French–Italian solar telescope THEMIS (Tenerife, Spain). Significant line-of-sight velocity time variations are found. At the beginning of the observations, the investigated region consisted of two areas of oppositely directed flows. The first area had a bright point in the vicinity of the pore and the second area covered the pore. There were upflows in the former and downflows in the latter. Oppositely directed flows appeared in both areas 2.7 min after the start of observations. In the part of the active region with a length of 2Mm, two oppositely directed flows within the same resolution elements, the so-called dual flows, were observed. The size of the area occupied by the dual flows varied quickly. The area shifted toward the pore. The velocity of upflows and downflows reached 25 km/s. The downflows in the first area lasted only for approximately 1 min. Upflows in the second area gradually covered the pore and lasted for 2 min. The resulting velocity field distribution can be due to a new small-scale magnetic flux emergence.  相似文献   

Spatial velocities of pulsars     

Yu. P. Pskovsky  O. F. Dorofeyev 《Journal of Astrophysics and Astronomy》1990,11(4):507-514

Assuming that the orientation of a pulsar’s velocity vector is parallel to its spin axis, we have calculated the space velocities of 61 pulsars from their tangential velocities. The mean space velocity of the sample is equal to 267 km s^-1. The radial velocities and kinematical ages of 20 pulsars are obtained. The decay time of the magnetic field of pulsars is τ_D = 2 Myr, smaller than previously found  相似文献   

The height variation of granular and oscillatory velocities     

Richard C. Canfield 《Solar physics》1976,50(2):239-254

Previous observations of spatially-resolved vertical velocity variations in ten lines of Fe i spanning the height range 0 h 1000 km are re-analyzed using velocity weighting functions. The amplitudes and scale heights of granular and oscillatory velocities are determined, as well as those of the remaining unresolved velocities. I find that the optimal representation of the amplitude of the outward-decreasing granular velocities is an exponentially decreasing function of height, with a scale height of 150 km and a velocity at zero height of 1.27 km s^–1. The optimal representation of the same quantities for oscillatory velocities is an exponential increase with height, with a scale height of 1100 km and a velocity at zero height of 0.35 km s^–1. The remaining unresolved velocities decrease with height, with a scale height of 380 km and a velocity at zero height of 2.3 km s^–1.  相似文献   

Mass and energy flow near sunspots     

Alan Nye  David Bruning  Barry J. Labonte 《Solar physics》1988,115(2):251-268

Sunspots block the flow of energy to the solar surface. The blocked energy heats the volume beneath the spot, producing a pressure excess which drives an outflow of mass. Linear numerical models of the mass and energy flow around spots were constructed to estimate the predictions of this physical picture against the observed properties of sunspot bright rings and moat flows. The width of the bright ring and moat are predicted to be proportional to the depth of the spot penumbra, in conflict with the observed proportionally of the moat width to the spot diameter. Postulating that spot depths are proportional to spot diameters would bury the moat flow too deeply to be observed, because the radial velocity at the surface is found to be inversely proportional to the depth of the spot penumbra. The radial velocity at the surface is of order a few hundred meters per second after 1 day, in agreement with the observed excess of moat velocities over supergranule velocities.  相似文献   

The Horizontal Component of Photospheric Plasma Flows During the Emergence of Active Regions on the Sun     

A. Khlystova 《Solar physics》2013,284(2):343-361

The dynamics of horizontal plasma flows during the first hours of the emergence of active region magnetic flux in the solar photosphere have been analyzed using SOHO/MDI data. Four active regions emerging near the solar limb have been considered. It has been found that extended regions of Doppler velocities with different signs are formed in the first hours of the magnetic flux emergence in the horizontal velocity field. The flows observed are directly connected with the emerging magnetic flux; they form at the beginning of the emergence of active regions and are present for a few hours. The Doppler velocities of flows observed increase gradually and reach their peak values 4?–?12 hours after the start of the magnetic flux emergence. The peak values of the mean (inside the ±?500 m?s^?1 isolines) and maximum Doppler velocities are 800?–?970 m?s^?1 and 1410?–?1700 m?s^?1, respectively. The Doppler velocities observed substantially exceed the separation velocities of the photospheric magnetic flux outer boundaries. The asymmetry was detected between velocity structures of leading and following polarities. Doppler velocity structures located in a region of leading magnetic polarity are more powerful and exist longer than those in regions of following polarity. The Doppler velocity asymmetry between the velocity structures of opposite sign reaches its peak values soon after the emergence begins and then gradually drops within 7?–?12 hours. The peak values of asymmetry for the mean and maximal Doppler velocities reach 240?–?460 m?s^?1 and 710?–?940 m?s^?1, respectively. An interpretation of the observable flow of photospheric plasma is given.  相似文献   

THE DEPTH DEPENDENCE OF PENUMBRAL ABSOLUTE VELOCITIES     

Balthasar  H.  Schmidt  W.  Wiehr  E. 《Solar physics》1997,171(2):331-336

Penumbral line-core shifts at different heights are determined from the lines Fei 5434.5 Å, Fei 5435.2 Å, and Nii 5435.8 Å using two adjacent water vapor lines for an absolute wavelength scale. The large granular blue shift of 0.6 km s^-1 for the faint Fe 5435 line from deep layers yields for the centre-side penumbra absolute velocities up to 3 km s^-1. This value is much larger than velocities deduced from the bisectors of the line wings of Ni 5436 and Fe 5434, thus supporting the concern against an interpretation of the line asymmetries in term of a velocity gradient with depth.  相似文献