scholarly journals Heightened Faraday complexity in the inner 1 kpc of the galactic centre

2021 ◽  
Vol 502 (3) ◽  
pp. 3814-3828
Author(s):  
J D Livingston ◽  
N M McClure-Griffiths ◽  
B M Gaensler ◽  
A Seta ◽  
M J Alger
Keyword(s):  
Galactic Plane ◽  
Small Scale ◽  
Order Structure ◽  
Galactic Centre ◽  
Outer Scale ◽  
Large Rotation ◽  
Stellar Feedback ◽  
Upper Limit ◽  
Centre Region ◽  
Scale Turbulence

ABSTRACT We have measured the Faraday rotation of 62 extra-galactic background sources in 58 fields using the CSIRO Australia Telescope Compact Array (ATCA) with a frequency range of 1.1–3.1 GHz with 2048 channels. Our sources cover a region $\sim 12\, \times 12\, \mathrm{deg^{ 2}}$ (∼1 kpc) around the Galactic Centre region. We show that the Galactic Plane for |l| < 10° exhibits large Rotation Measures (RMs) with a maximum |RM| of $1691.2 \pm 4.9\, \mathrm{rad}\, \mathrm{m}^{-2}$ and a mean $|\mathrm{RM}| = 219 \pm 42\, \mathrm{rad}\, \mathrm{m}^{-2}$. The RMs decrease in magnitude with increasing projected distance from the Galactic Plane, broadly consistent with previous findings. We find an unusually high fraction (95 per cent) of the sources show Faraday complexity consistent with multiple Faraday components. We attribute the presences of multiple Faraday rotating screens with widely separated Faraday depths to small-scale turbulent RM structure in the Galactic Centre region. The second-order structure function of the RM in the Galactic Centre displays a line with a gradient of zero for angular separations spanning 0.83°–11° (∼120–1500 pc), which is expected for scales larger than the outer scale (or driving scale) of magneto-ionic turbulence. We place an upper limit on any break in the SF gradient of 66 arcsec, corresponding to an inferred upper limit to the outer scale of turbulence in the inner 1 kpc of the Galactic Centre of 3 pc. We propose stellar feedback as the probable driver of this small-scale turbulence.

Interstellar gas in the central region of the Galaxy

1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr
Keyword(s):  
Central Region ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Interstellar Gas ◽  
Hydrogen Recombination ◽  
The Galaxy ◽  
Centre Region ◽  
The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

Some statistical properties of small scale turbulence in an atmospheric boundary layer

1970 ◽  
Vol 41 (1) ◽  
pp. 141-152 ◽  
Author(s):  
R. W. Stewart ◽  
J. R. Wilson ◽  
R. W. Burling
Keyword(s):  
Boundary Layer ◽  
Lognormal Distribution ◽  
A Priori ◽  
Inertial Subrange ◽  
Small Scale ◽  
Order Structure ◽  
Third Order ◽  
The Difference ◽  
Scale Turbulence ◽  
Derivatives Of

Derivatives of velocity signals obtained in a turbulent boundary layer are examined for correspondence to the lognormal distribution. It is found that there is rough agreement but that unlikely events at high values are much less common in the observed fields than would be inferred from the lognormal distribution. The actual distributions correspond more to those obtained from a random walk with a limited number of steps, so the difference between these distributions and the lognormal may be related to the fact that the Reynolds number is finite.The third-order structure function is examined, and found to be roughly consistent with the existence of an inertial subrange of a Kolmogoroff equilibrium reacute;gime over a range of scale which is a priori reasonable but which is far less extensive than the $-\frac{5}{3}$ region of the spectrum.

scholarly journals Numerical Models of 3-D Galactic Dynamos

1993 ◽  
Vol 157 ◽  
pp. 345-348
Author(s):  
J.S. Panesar ◽  
N. Moore ◽  
A.H. Nelson
Keyword(s):  
Numerical Models ◽  
Density Wave ◽  
Vertical Component ◽  
Small Scale ◽  
Galactic Centre ◽  
Model Parameters ◽  
Magnetic Intensity ◽  
Field Mode ◽  
The Galaxy ◽  
Scale Turbulence

We describe here the results of 3-D numerical simulations of an αω-dynamo in galaxies with differential rotation, small scale turbulence, and a shock wave induced by a stellar density wave. A non-linear quenching mechanism for the dynamo instability is used, and with the model parameters employed the field achieves a steady state which closely resembles observed fields in galaxies. The magnetic field vectors are parallel to the plane in the disc, with the magnetic intensity decreasing away from the plane. The vectors are also nearly parallel to the spiral arms in the disc, and the field direction is axisymmetric about the galactic centre, but with significant increase of intensity in the arms. The magnetic intensity rises steeply towards the centre of the galaxy, where the field becomes dominated by the vertical component. Nowhere in the parameter range covered is the bi-symmetric field mode dominant.

The Galactic Centre

1974 ◽  
Vol 60 ◽  
pp. 539-547 ◽  
Author(s):  
J. H. Oort
Keyword(s):  
Central Region ◽  
Molecular Clouds ◽  
Direct Evidence ◽  
Galactic Plane ◽  
High Rate ◽  
Small Scale ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Complicated Structure ◽  
Sgr A

The phenomena displayed by the interstellar medium in the galactic centre are considered. The asymmetries shown by the features between 1 and 3 kpc from the centre together with the presence of material lying out of the galactic plane favour the expulsion hypothesis for their origin. The nuclear disk shows a perturbation which might have resulted from such expulsion. The dense molecular clouds in the disk may well be considered as the most direct evidence that matter is expelled from the nucleus and that this occurs at a high rate. The +50 km s-1 feature in the direction of Sgr A may be the most recently expelled body of molecular gas. New observations of the central radio source, Sgr A, have revealed details on a very small scale, and the infrared core also shows a complicated structure. Probably a number of individual concentrations of gas and dust are present. While the position of the actual nucleus seems now to have been defined to within a few arcseconds, no indication has yet been found concerning its nature nor concerning the mechanism that enables it to expel the vast expanding masses of gas observed in the central region.

scholarly journals The Production of Rotation Measure Gradients in the Lobes of Extragalactic Radio Sources

1990 ◽  
Vol 140 ◽  
pp. 477-481
Author(s):  
G.V. Bicknell ◽  
R.A. Cameron ◽  
R.A. Gingold
Keyword(s):  
Magnetic Field ◽  
Surrounding Medium ◽  
Small Scale ◽  
Radio Sources ◽  
Large Rotation ◽  
Extragalactic Radio Sources ◽  
Cygnus A ◽  
Rotation Measure ◽  
Order Of Magnitude ◽  
Scale Turbulence

It is proposed that the large rotation measure gradients observed in the lobes of some extragalactic radio sources are produced by non–linear Kelvin–Helmholtz surface waves. Related small scale turbulence is responsible for a “diffuse spray” of relativistic plasma and magnetic field into the surrounding medium. The mixture of magnetic field and thermal plasma causes large rotation measure variations on the scale of the Kelvin–Helmholtz waves. An order of magnitude prediction of the effect is in good agreement with the observations of Cygnus A and PKS 2104–25 N.

scholarly journals Birthing star forming clouds in the grand design

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Yusuke Fujimoto ◽  
Elizabeth J. Tasker ◽  
Greg L. Bryan ◽  
Asao Habe
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Galactic Centre ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Stellar Feedback ◽  
Star Formation Activity ◽  
Grand Design ◽  
Centre Region ◽  
Hydrodynamical Simulations

AbstractWe performed high resolution 3D hydrodynamical simulations of the barred galaxy M83 and investigated formation and evolution of the giant molecular clouds (GMCs) and star formation activity. We compared two simulations with and without stellar feedback. We found that the feedback disperses the cloud gas and causes clouds to inflow toward the galactic centre region due to hydrodynamical drag. The effect raises the star formation rate (SFR) and star formation efficiency (SFE) in the central bar region.

Temporal Evolution and Scaling of Mixing in Turbulent Thermal Convection for Inhomogeneous Boundary Conditions

2017 ◽  
Vol 9 (5) ◽  
pp. 1035-1051
Author(s):  
Yikun Wei ◽  
Hua-Shu Dou ◽  
Zuchao Zhu ◽  
Zhengdao Wang ◽  
Yuehong Qian ◽  
...  
Keyword(s):  
Thermal Convection ◽  
Large Scale ◽  
Temporal Evolution ◽  
Thermal Dissipation ◽  
Small Scale ◽  
Order Structure ◽  
Temperature Structure ◽  
Dissipation Rates ◽  
Theoretical Predictions ◽  
Scale Turbulence

AbstractNumerical simulations of two-dimensional (2D) turbulent thermal convection for inhomogeneous boundary condition are investigated using the lattice Boltzmann method (LBM). This study mainly appraises the temporal evolution and the scaling behavior of global quantities and of small-scale turbulence properties. The research results show that the flow is dominated by large-scale structures in the turbulence regime. Mushroom plumes emerge at both ends of each heat source, and smaller plumes increasingly rise. It is found that the gradient of root mean-square (rms) vertical velocities and the gradient of the rms temperature in the bottom boundary layer decreases with time evolution. It is further observed that the temporal evolution of the Kolmogorov scale, the kinetic-energy dissipation rates and thermal dissipation rates agree well with the theoretical predictions. It is also observed that there is a range of linear scaling in the 2nd-order structure functions of the velocity and temperature fluctuations and mixed velocity-temperature structure function.

Progress report on 21-cm observations at low latitude between longitudes (l 11) 0° and 66°

1967 ◽  
Vol 31 ◽  
pp. 177-179
Author(s):  
W. W. Shane
Keyword(s):  
Preliminary Report ◽  
Progress Report ◽  
Galactic Centre ◽  
Low Latitude ◽  
The Third ◽  
Introductory Lecture ◽  
Centre Region

In the course of several 21-cm observing programmes being carried out by the Leiden Observatory with the 25-meter telescope at Dwingeloo, a fairly complete, though inhomogeneous, survey of the regionl11= 0° to 66° at low galactic latitudes is becoming available. The essential data on this survey are presented in Table 1. Oort (1967) has given a preliminary report on the first and third investigations. The third is discussed briefly by Kerr in his introductory lecture on the galactic centre region (Paper 42). Burton (1966) has published provisional results of the fifth investigation, and I have discussed the sixth in Paper 19. All of the observations listed in the table have been completed, but we plan to extend investigation 3 to a much finer grid of positions.

Observations of the continuum near the galactic centre

1967 ◽  
Vol 31 ◽  
pp. 405
Author(s):  
F. J. Kerr
Keyword(s):  
Galactic Centre ◽  
The Past ◽  
Centre Region ◽  
The Continuum

A continuum survey of the galactic-centre region has been carried out at Parkes at 20 cm wavelength over the areal11= 355° to 5°,b11= -3° to +3° (Kerr and Sinclair 1966, 1967). This is a larger region than has been covered in such surveys in the past. The observations were done as declination scans.

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