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Register a new userAccurate Parameters of the Mass Distribution in Spiral Galaxies: 1. Fabry - Perot Observations of NGC 5585
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Sebastien Blais-Ouellette
Publication date
1999
fields
Physics
and research's language is
English
Authors
Sebastien Blais-Ouellette
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Using the example of the Sd galaxy NGC 5585, it is shown that high resolution 2-D HII kinematical data are necessary to determine accurately the parameters of the mass distribution in spirals. New CFHT Fabry-Perot Halpha observations are combined with low resolution (20) Westerbork HI data to study its mass distribution. Using the combined rotation curve and best fit models, it can be seen that M/L of the luminous disk goes from 0.3 using only the HI rotation curve, to 0.8 using both the optical and the radio data. This reduces the dark-to-luminous mass ratio in NGC 5585 by ~30% through increasing the dark matter halo core radius by nearly the same amount. This shows the importance of the inner, rising part of the rotation curve for the accurate determination of the parameters of the global mass (luminous & dark) distribution and suggests that such a fine tuning of the rotation velocities using high resolution 2-D HII kinematics is necessary to look at correlations between the parameters of the dark matter component and other properties of galaxies.
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High resolution Fabry-Perot data of six spiral galaxies are presented. Those data extend the previous sample of spiral galaxies studied with high resolution 3D spectroscopy to earlier morphological types. All the galaxies in the sample have available HI data at 21 cm from the VLA or Westerbork. Velocity fields are analyzed and Halpha rotation curves are computed and compared to HI curves. The kinematics of NGC 5055 central regions are looked at more closely. Its peculiar kinematics can be interpreted either as a bipolar outflow or as a counter-rotating disk, possibly hosting a 9 pm 2 10^8 Msol compact object. Most of the Halpha rotation curves present a significantly steeper inner slope than their HI counterparts. The 21 cm data thus seems affected by moderate to strong beam smearing. The beam smearing has an effect at higher scale-length/beam-width than previously thought (up to 20 km/s at a ratio of 8.5).
We have obtained a Halpha position-velocity cube from Fabry-Perot interferometric observations of the HH 110 flow. We analyze the results in terms of anisotropic wavelet transforms, from which we derive the spatial distribution of the knots as well as their characteristic sizes (along and across the outflow axis). We then study the spatial behaviour of the line width and the central radial velocity. The results are interpreted in terms of a simple ``mean flow+turbulent eddy jet/wake model. We find that most of the observed kinematics appear to be a direct result of the mean flow, on which are superposed low amplitude (35 km/s) turbulent velocities.
New high resolution CFHT Fabry-Perot data, combined with published VLA 21 cm observations are used to determine the mass distribution of NGC 3109 and IC 2574. The multi-wavelength rotation curves allow to test with confidence different dark halo functional forms from the pseudo-isothermal sphere to some popular halo distributions motivated by N-body simulations. It appears that density distribution with an inner logarithmic slope <= -1 are very hard to reconcile with rotation curves of late type spirals. Modified Newtonian Dynamics (MOND) is also considered as a potential solution to missing mass and tested the same way. The new higher resolution data show that MOND can reproduce in details the rotation curve of IC 2574 but confirm its difficulty to fit the kinematics of NGC 3109.
We show that significant water wave amplification is obtained in a water resonator consisting of two spatially separated patches of small-amplitude sinusoidal corrugations on an otherwise flat seabed. The corrugations reflect the incident waves according to the so-called Bragg reflection mechanism, and the distance between the two sets controls whether the trapped reflected waves experience constructive or destructive interference within the resonator. The resulting amplification or suppression is enhanced with increasing number of ripples, and is most effective for specific resonator lengths and at the Bragg frequency, which is determined by the corrugation period. Our analysis draws on the analogous mechanism that occurs between two partially reflecting mirrors in optics, a phenomenon named after its discoverers Charles Fabry and Alfred Perot.
We show how to analyze the motion of very low dissipation suspended mirrors in a Fabry-Perot. The very precise measurements of the mirrors motion can be determined, also in the presence of a disturbing noise, by means of the sudden reflectivity changes in special points of the mirrors positions. When the mirrors cross such positions, the effective opto-mechanical potential that arises in the device is (roughly) at a maximum. We show that the motion cross such potential maxima is not only confused by the presence of noise, but also favoured by noise itself that induces hoppings. Thus, the measurements of the times at which the crossings occur can be exploited to identify the properties of the applied signal. We also show how to circumvent the difficulty of the extremely long transient that occur in the system analyzing the escape average time with two different methods: a direct sample average and the indirect estimate from the tail distribution. Numerical simulations and physical insight suggest that the indirect estimate, through the analysis of the distribution tails with an appropriated cut off is robust against the disturbances that arise from the presence of transient dynamics.
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