scholarly journals Disk Stability and Turbulence Generation: Effects of the Stellar Component

2008 ◽  
Vol 4 (S254) ◽  
pp. 313-318
Author(s):  
Woong-Tae Kim
Keyword(s):  
Kinetic Energy ◽  
Strong Shock ◽  
Gas Flows ◽  
Spiral Arms ◽  
Stellar Component ◽  
Magnetic Tension ◽  
Turbulence Generation ◽  
Unstable Intermediate ◽  
Spiral Arm ◽  
Shock Dissipation

AbstractGalactic disks consist of both stars and gas. The stars gravitationally influence the gas either in disks at large or within spiral arms, leading to the formation of giant clouds and turbulence driving in the gas. In featureless disks as in flocculent galaxies, swing amplification operating in a combined star-gas disk is efficient to form bound condensations and feed a significant level of random gas motions. This occurs when the gaseous Toomre parameter is less than 1.4 for the stellar parameters similar to the solar neighbourhood conditions. In disks with spiral features, on the other hand, spiral-arm spurs and associated giant clouds develop as a consequence of magneto-Jeans instability in which magnetic tension counterbalances the stabilizing Coriolis force. Spiral shocks are inherently unstable when the vertical dimension is taken into account, exhibiting flapping motions of the shock front. This naturally converts the kinetic energy in galaxy rotation into random kinetic energy of the gas. The resulting turbulent motions are supersonic and persist despite strong shock dissipation. Thermal instability occurring in gas flows across spiral arms prompts phases transitions that produce a significant fraction of thermally-unstable, intermediate-temperature gas in the postshock expansion zones.

scholarly journals Two-component galaxy models with a central BH – II. The ellipsoidal case

2020 ◽  
Vol 500 (1) ◽  
pp. 1054-1070
Author(s):  
Luca Ciotti ◽  
Antonio Mancino ◽  
Silvia Pellegrini ◽  
Azadeh Ziaee Lorzad
Keyword(s):  
Dark Matter ◽  
Stellar Dynamics ◽  
Azimuthal Velocity ◽  
Dark Matter Halo ◽  
Gas Flows ◽  
Total Density ◽  
Density Distributions ◽  
Stellar Component ◽  
Two Component ◽  
Analytical Formulae

ABSTRACT Recently, two-component spherical galaxy models have been presented, where the stellar profile is described by a Jaffe law, and the total density by another Jaffe law, or by an r−3 law at large radii. We extend these two families to their ellipsoidal axisymmetric counterparts: the JJe and J3e models. The total and stellar density distributions can have different flattenings and scale lengths, and the dark matter halo is defined by difference. First, the analytical conditions required to have a nowhere negative dark matter halo density are derived. The Jeans equations for the stellar component are then solved analytically, in the limit of small flattenings, also in the presence of a central BH. The azimuthal velocity dispersion anisotropy is described by the Satoh k-decomposition. Finally, we present the analytical formulae for velocity fields near the centre and at large radii, together with the various terms entering the virial theorem. The JJe and J3e models can be useful in a number of theoretical applications, e.g. to explore the role of the various parameters (flattening, relative scale lengths, mass ratios, rotational support) in determining the behaviour of the stellar kinematical fields before performing more time-expensive integrations with specific galaxy models, to test codes of stellar dynamics and in numerical simulations of gas flows in galaxies.

scholarly journals Autonomous Gaussian decomposition of the Galactic Ring Survey

2020 ◽  
Vol 640 ◽  
pp. A72
Author(s):  
M. Riener ◽  
J. Kainulainen ◽  
J. D. Henshaw ◽  
H. Beuther
Keyword(s):  
Milky Way ◽  
Velocity Dispersion ◽  
Galactic Plane ◽  
Gas Emission ◽  
Spiral Arms ◽  
Precise Knowledge ◽  
Significant Difference ◽  
The Impact ◽  
Co Emission ◽  
Spiral Arm

Knowledge about the distribution of CO emission in the Milky Way is essential to understanding the impact of the Galactic environment on the formation and evolution of structures in the interstellar medium. However, our current insight as to the fraction of CO in the spiral arm and interarm regions is still limited by large uncertainties in assumed rotation curve models or distance determination techniques. In this work we use the Bayesian approach from Reid et al. (2016, ApJ, 823, 77; 2019, ApJ, 885, 131), which is based on our most precise knowledge at present about the structure and kinematics of the Milky Way, to obtain the current best assessment of the Galactic distribution of 13CO from the Galactic Ring Survey. We performed two different distance estimates that either included (Run A) or excluded (Run B) a model for Galactic features, such as spiral arms or spurs. We also included a prior for the solution of the kinematic distance ambiguity that was determined from a compilation of literature distances and an assumed size-linewidth relationship. Even though the two distance runs show strong differences due to the prior for Galactic features for Run A and larger uncertainties due to kinematic distances in Run B, the majority of their distance results are consistent with each other within the uncertainties. We find that the fraction of 13CO emission associated with spiral arm features ranges from 76 to 84% between the two distance runs. The vertical distribution of the gas is concentrated around the Galactic midplane, showing full-width at half-maximum values of ~75 pc. We do not find any significant difference between gas emission properties associated with spiral arm and interarm features. In particular, the distribution of velocity dispersion values of gas emission in spurs and spiral arms is very similar. We detect a trend of higher velocity dispersion values with increasing heliocentric distance, which we, however, attribute to beam averaging effects caused by differences in spatial resolution. We argue that the true distribution of the gas emission is likely more similar to a combination of the two distance results discussed, and we highlight the importance of using complementary distance estimations to safeguard against the pitfalls of any single approach. We conclude that the methodology presented in this work is a promising way to determine distances to gas emission features in Galactic plane surveys.

scholarly journals The Two Component Magnetic Field of the Galaxy

1990 ◽  
Vol 140 ◽  
pp. 54-54
Author(s):  
R.R. Andreassian ◽  
A.N. Makarov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Configuration ◽  
Radio Sources ◽  
Magnetic Field Configuration ◽  
Spiral Arms ◽  
Two Component ◽  
The Galaxy ◽  
The Magnetic Field ◽  
Spiral Arm

The present paper is devoted to a study of the magnetic field configuration of our Galaxy based on Faraday rotation measures (RM) of 185 pulsars and 802 extragalactic radio sources. RM data of pulsars located near the plane of the Galaxy are used for the study of magnetic fields in neighbouring spiral arms. For the distribution of spiral arms the well-known model of Georgelin and Georgelin (1976) is used. The calculations show (for details see Andreassian and Makarov, 1987, 1989) that in the Perseus spiral arm and the local Orion arm the magnetic fields have approximately the same directions (lo;bo) ≈ (80°;0°), while in the Sagittarius-Carina arm the magnetic field has an opposite direction.

scholarly journals Interarm islands in the Milky Way – the one near the Cygnus spiral arm

2020 ◽  
Vol 494 (1) ◽  
pp. 1134-1142
Author(s):  
Jacques P Vallée
Keyword(s):  
Observational Data ◽  
Milky Way ◽  
Young Stars ◽  
H Ii Regions ◽  
Spiral Arms ◽  
The Galaxy ◽  
The One ◽  
Loop 2 ◽  
Perseus Arm ◽  
Spiral Arm

ABSTRACT This study extends to the structure of the Galaxy. Our main goal is to focus on the first spiral arm beyond the Perseus arm, often called the Cygnus arm or the ‘Outer Norma’ arm, by appraising the distributions of the masers near the Cygnus arm. The method is to employ masers whose trigonometric distances were measured with accuracy. The maser data come from published literature – see column 8 in Table 1 here, having been obtained via the existing networks (US VLBA, the Japanese VERA, the European VLBI, and the Australian LBA). The new results for Cygnus are split in two groups: those located near a recent CO-fitted global model spiral arm and those congregating within an ‘interarm island’ located halfway between the Perseus arm and the Cygnus arm. Next, we compare this island with other similar interarm objects near other spiral arms. Thus, we delineate an interarm island (6 × 2 kpc) located between the two long spiral arms (Cygnus and Perseus arms); this is reminiscent of the small ‘Local Orion arm’ (4 × 2 kpc) found earlier between the Perseus and Sagittarius arms and of the old ‘Loop’ (2 × 0.5 kpc) found earlier between the Sagittarius and Scutum arms. Various arm models are compared, based on observational data (masers, H II regions, H I gas, young stars, CO 1–0 gas).

scholarly journals Substructure within galactic spiral arms as derived from studies at 21 cm

1959 ◽  
Vol 9 ◽  
pp. 355-359
Author(s):  
R. D. Davies
Keyword(s):  
Fine Structure ◽  
High Resolution ◽  
Velocity Dispersion ◽  
Detailed Structure ◽  
Hydrogen Line ◽  
Spiral Arms ◽  
Frequency Structure ◽  
Galactic Spiral ◽  
Spiral Arm

Detailed structure within the spiral arms of our Galaxy is suggested by hydrogen-line spectra taken with high resolution in frequency [1]. The spectra show much detail in each maximum (spiral arm). It is not clear, however, if this frequency structure refers to fine structure in depth or in velocity dispersion or in both. Fine structure in position and depth has been inferred from 21-cm drift curves taken across the nearby spiral arms. The results of three investigations will be discussed. Two have been published in some detail [2, 3] and will only be summarized here.

scholarly journals The role of cold and hot gas flows in feeding early-type galaxy formation

2014 ◽  
Vol 11 (S308) ◽  
pp. 394-397
Author(s):  
Peter H. Johansson
Keyword(s):  
Galaxy Formation ◽  
Gas Flows ◽  
Early Type ◽  
Gas Streams ◽  
Hot Gas ◽  
Stellar Component ◽  
The Galaxy ◽  
History Of ◽  
Gas Accretion ◽  
Low Entropy

AbstractWe study the evolution of the gaseous components in massive simulated galaxies and show that their early formation is fuelled by cold, low entropy gas streams. At lower redshifts of z ≲ 3 the simulated galaxies are massive enough to support stable virial shocks resulting in a transition from cold to hot gas accretion. The gas accretion history of early-type galaxies is directly linked to the formation of their stellar component in the two phased formation scenario, in which the central parts of the galaxy assemble rapidly through in situ star formation and the later assembly is dominated primarily by minor stellar mergers.

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