The Power Spectrum of Supersonic Turbulence in Perseus

ArticleinThe Astrophysical Journal 653(2) · November 2006with5 Reads
DOI: 10.1086/510620 · Source: arXiv
Abstract
We test a method of estimating the power spectrum of turbulence in molecular clouds based on the comparison of power spectra of integrated intensity maps and single-velocity-channel maps, suggested by Lazarian and Pogosyan. We use synthetic 13CO data from non-LTE radiative transfer calculations based on density and velocity fields of a simulation of supersonic hydrodynamic turbulence. We find that the method yields the correct power spectrum with good accuracy. We then apply the method to the Five College Radio Astronomy Observatory 13CO map of the Perseus region, from the COMPLETE website. We find a power law power spectrum with slope beta=1.81+-0.10. The values of beta as a function of velocity resolution are also confirmed using the lower resolution map of the same region obtained with the AT&T Bell Laboratories antenna. Because of its small uncertainty, this result provides a useful constraint for numerical codes used to simulate molecular cloud turbulence. Comment: 4 pages, 3 figures. ApJ Letters, in press
    • "As new techniques for studying turbulence are being applied to observational data, the evidence of the turbulent nature of astrophysical media becomes really undeniable. For instance, the Velocity Channel Analysis (VCA) and Velocity Coordinate Spectrum (VCS) techniques (Lazarian and Pogosyan, 2000) provided unique insight into the velocity spectra of turbulence in molecular clouds (see Padoan et al, 2006 Padoan et al, , 2010), galactic and extragalactic atomic hydrogen (Stanimirovi´cStanimirovi´c and Lazarian (2001); Chepurnov et al ( , 2015, see also the review by Lazarian (2009) , where a compilation of velocity and density spectra obtained with contemporary HI and CO data is presented). We expect new flow of information on magnetic field spectra to come from the new techniques that treat synchrotron fluctuations (Lazarian and Pogosyan, 2012). "
    [Show abstract] [Hide abstract] ABSTRACT: Realistic astrophysical environments are turbulent due to the extremely high Reynolds numbers. Therefore, the theories of reconnection intended for describing astrophysical reconnection should not ignore the effects of turbulence on magnetic reconnection. Turbulence is known to change the nature of many physical processes dramatically and in this review we claim that magnetic reconnection is not an exception. We stress that not only astrophysical turbulence is ubiquitous, but also magnetic reconnection itself induces turbulence. Thus turbulence must be accounted for in any realistic astrophysical reconnection setup. We argue that due to the similarities of MHD turbulence in relativistic and non-relativistic cases the theory of magnetic reconnection developed for the non-relativistic case can be extended to the relativistic case and we provide numerical simulations that support this conjecture. We also provide quantitative comparisons of the theoretical predictions and results of numerical experiments, including the situations when turbulent reconnection is self-driven, i.e. the turbulence in the system is generated by the reconnection process itself. We show how turbulent reconnection entails the violation of magnetic flux freezing, the conclusion that has really far reaching consequences for many realistically turbulent astrophysical environments. In addition, we consider observational testing of turbulent reconnection as well as numerous implications of the theory. The former includes the Sun and solar wind reconnection, while the latter include the process of reconnection diffusion induced by turbulent reconnection, the acceleration of energetic particles, bursts of turbulent reconnection related to black hole sources as well as gamma ray bursts. Finally, we explain why turbulent reconnection cannot be explained by turbulent resistivity or derived through the mean field approach.
    Full-text · Article · Dec 2015 · Journal of Plasma Physics
    A. LazarianA. LazarianG. KowalG. KowalM. TakamotoM. Takamoto+1more author...[...]
    • "Initially, the volume was considered transparent, but later the treatment was generalized to volumes with self-absorption and to studies of turbulence using absorption lines (Lazarian and Pogosyan 2004, 2008). The resulting theory of mapping of fluctuations in Position-Position-Position space with turbulent velocity into PPV space was successfully tested in a number of studies (Padoan et al. 2006Padoan et al. , 2009 Chepurnov and Lazarian 2009; Burkhart et al. 2013). This theory lays the foundation for two separate techniques, Velocity Channel Analysis (VCA) and Velocity Correlation Spectrum (VCS) which were applied by MHD turbulence theory is in many respects similar to the famous Kolmogorov (1941) theory of turbulence. "
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    Full-text · Article · Jul 2013
    • "Besides the well known density fluctuation spectra also velocity power spectra may be obtained. One possible method for this has been presented by Lazarian & Pogosyan (1997) and was applied by Padoan et al. (2006). The connection between the velocity and density observations are not fully understood, as pointed out by Klessen (2000). "
    [Show abstract] [Hide abstract] ABSTRACT: Turbulence in the interstellar medium has been an active field of research in the last decade. Numerical simulations are the tool of choice in most cases. But while there are a number of simulations on the market some questions have not been answered finally. In this paper we are going to examine the influence of compressible and incompressible driving on the evolution of turbulent spectra in a number of possible interstellar medium scenarios. We conclude that the driving not only has an influence on the ratio of compressible to incompressible component but also on the anisotropy of turbulence.
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