Spiral structure and star formation. II - Stellar lifetimes and cloud kinematics

1984 ◽  
Vol 282 ◽  
pp. 106 ◽  
Author(s):  
M. A. Hausman ◽  
W. W., Jr. Roberts
Keyword(s):  
Star Formation ◽  
Spiral Structure ◽  
Cloud Kinematics

scholarly journals An overview of the structure and kinematics of the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 15-23 ◽  
Author(s):  
B. E. Westerlund
Keyword(s):  
Star Formation ◽  
Observational Data ◽  
Spiral Structure ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Line Of Sight ◽  
Small Magellanic Cloud ◽  
Complex Velocity ◽  
The Past

A vast amount of observational data concerning the structure and kinematics of the Magellanic Clouds is now available. Many basic quantities (e.g. distances and geometry) are, however, not yet sufficiently well determined. Interactions between the Small Magellanic Cloud (SMC), the Large Magellanic Cloud (LMC) and our Galaxy have dominated the evolution of the Clouds, causing bursts of star formation which, together with stochastic self-propagating star formation, produced the observed structures. In the youngest generation in the LMC it is seen as an intricate pattern imitating a fragmented spiral structure. In the SMC much of the fragmentation is along the line of sight complicating the reconstruction of its history. The violent events in the past are also recognizable in complex velocity patterns which make the analysis of the kinematics of the Clouds difficult.

scholarly journals Selfpropagating Stochastic Star Formation and Spiral Structure

1983 ◽  
Vol 100 ◽  
pp. 141-142 ◽  
Author(s):  
J. V. Feitzinger ◽  
P. E. Seiden
Keyword(s):  
Star Formation ◽  
Spiral Structure ◽  
Relative Importance ◽  
Formation Model ◽  
Density Waves ◽  
Spiral Density Waves ◽  
Two Component ◽  
Grand Design ◽  
Dynamic Phenomena

Spiral structure in galaxies can arise from both dynamic and non dynamic phenomena: spiral density waves and stochastic selfpropagating star formation. The relative importance of these effects is still not known. Deficiences of the original selfpropagating star formation model (where only stars are taken into account) are overcome by explicitly considering the stars embedded in and interacting with a two-component gas (Seiden and Gerola, 1979; Seiden, Schulman and Feitzinger, 1982; Seiden and Gerola, 1982). The two-component gas is essential because it is the means by which we get feedback in the interaction between stars and gas. The coupling between stars and gas regulates and stabilizes star formation in a galaxy. Under proper conditions this model can give good grand design spirals (Fig. 1).

scholarly journals The relation between the turbulent Mach number and observed fractal dimensions of turbulent clouds

2019 ◽  
Vol 488 (2) ◽  
pp. 2493-2502 ◽  
Author(s):  
James R Beattie ◽  
Christoph Federrath ◽  
Ralf S Klessen ◽  
Nicola Schneider
Keyword(s):  
Fractal Dimension ◽  
Star Formation ◽  
Mach Number ◽  
Column Density ◽  
Velocity Dispersion ◽  
Error Function ◽  
Empirical Relation ◽  
Three Dimensional ◽  
Fractal Dimensions ◽  
Cloud Kinematics

Abstract Supersonic turbulence is a key player in controlling the structure and star formation potential of molecular clouds (MCs). The three-dimensional (3D) turbulent Mach number, $\operatorname{\mathcal {M}}$, allows us to predict the rate of star formation. However, determining Mach numbers in observations is challenging because it requires accurate measurements of the velocity dispersion. Moreover, observations are limited to two-dimensional (2D) projections of the MCs and velocity information can usually only be obtained for the line-of-sight component. Here we present a new method that allows us to estimate $\operatorname{\mathcal {M}}$ from the 2D column density, Σ, by analysing the fractal dimension, $\mathcal {D}$. We do this by computing $\mathcal {D}$ for six simulations, ranging between 1 and 100 in $\operatorname{\mathcal {M}}$. From this data we are able to construct an empirical relation, $\log \operatorname{\mathcal {M}}(\mathcal {D}) = \xi _1(\operatorname{erfc}^{-1} [(\mathcal {D}-\operatorname{\mathcal {D}_\text{min}})/\Omega ] + \xi _2),$ where $\operatorname{erfc}^{-1}$ is the inverse complimentary error function, $\operatorname{\mathcal {D}_\text{min}}= 1.55 \pm 0.13$ is the minimum fractal dimension of Σ, Ω = 0.22 ± 0.07, ξ1 = 0.9 ± 0.1, and ξ2 = 0.2 ± 0.2. We test the accuracy of this new relation on column density maps from Herschel observations of two quiescent subregions in the Polaris Flare MC, ‘saxophone’ and ‘quiet’. We measure $\operatorname{\mathcal {M}}\sim 10$ and $\operatorname{\mathcal {M}}\sim 2$ for the subregions, respectively, which are similar to previous estimates based on measuring the velocity dispersion from molecular line data. These results show that this new empirical relation can provide useful estimates of the cloud kinematics, solely based upon the geometry from the column density of the cloud.

scholarly journals Magnetic Fields and Spiral Structure

1983 ◽  
Vol 100 ◽  
pp. 159-160 ◽  
Author(s):  
R. Beck
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Milky Way ◽  
Spiral Structure ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Radio Telescopes ◽  
Evolution Of Galaxies ◽  
Structure Strength ◽  
Spiral Structures

Interstellar magnetic fields are known to be a constraint for star formation, but their influence on the formation of spiral structures and the evolution of galaxies is generally neglected. Structure, strength and degree of uniformity of interstellar magnetic fields can be determined by measuring the linearly polarised radio continuum emission at several frequencies (e.g. Beck, 1982). Results for 7 galaxies observed until now with the Effelsberg and Westerbork radio telescopes are given in the table. The Milky Way is also included for comparison.

scholarly journals Stochastic star formation and spiral structure

1985 ◽  
Vol 106 ◽  
pp. 551-558
Author(s):  
Philip E. Seiden
Keyword(s):  
Star Formation ◽  
Long Range ◽  
Molecular Cloud ◽  
Short Range ◽  
Spiral Structure ◽  
Open Cluster ◽  
Gravitational Interaction ◽  
Range Order ◽  
Ionization Front ◽  
Long Range Order

Most approaches to explaining the long-range order of the spiral arms in galaxies assume that it is induced by the long-range gravitational interaction. However, it is well-known in many fields of physics that long-range order may be induced by short-range interactions. A typical example is magnetism, where the exchange interaction between magnetic spins has a range of only 10 ångströms, yet a bar magnet can be made as large as one likes. Stochastic self-propagating star formation (SSPSF) starts from the point of view of a short-range interaction and examines the spiral structure arising from it (Seiden and Gerola 1982). We assume that the energetic processes of massive stars, stellar winds, ionization-front shocks and supernova shocks, in an OB association or open cluster can induce the creation of a new molecular cloud from cold interstellar atomic hydrogen. In turn this new molecular cloud will begin to form stars that will allow the process to repeat, creating a chain reaction. The differential rotation existing in a spiral galaxy will stretch the aggregation of recently created stars into spiral features.

scholarly journals Formation of Giant Molecular Clouds by Coagulation of Small Molecular Clouds in a Spiral Gravitational Potential

1987 ◽  
Vol 115 ◽  
pp. 541-543
Author(s):  
Kohji Tomisaka
Keyword(s):  
Star Formation ◽  
Time Evolution ◽  
Gravitational Potential ◽  
Formation Process ◽  
Molecular Clouds ◽  
Spiral Structure ◽  
Giant Molecular Clouds ◽  
Short Lifetime ◽  
Spiral Arm

The formation process of giant molecular clouds (GMCs) is investigated from the standpoint of the coagulation theory of molecular clouds. Small clouds collide with each other and grow to become massive ones. Ultimately they form GMCs with a finite lifetime. The occurrence of star formation in a GMC destroys it and consequently small clouds are formed again. We study the time evolution of the clouds which move through a spiral gravitational potential by an N-body simulation. Then the ensemble of clouds responds to the spiral potential and forms a spiral structure similar to that produced by hydrodynamical galactic shock. It is shown that GMCs are formed in the spiral arm region by collisions between clouds. The distribution of GMCs indicates their short lifetime, of the order of a few times 107 years.

scholarly journals Distribution and kinematics of 26Al in the Galactic disc

2020 ◽  
Vol 497 (2) ◽  
pp. 2442-2454 ◽  
Author(s):  
Yusuke Fujimoto ◽  
Mark R Krumholz ◽  
Shu-ichiro Inutsuka
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Spiral Structure ◽  
Rotation Speed ◽  
Scale Height ◽  
Stellar Winds ◽  
Galactic Disc ◽  
Stellar Feedback ◽  
Self Gravity ◽  
Solar Position

ABSTRACT 26Al is a short-lived radioactive isotope thought to be injected into the interstellar medium (ISM) by massive stellar winds and supernovae (SNe). However, all-sky maps of 26Al emission show a distribution with a much larger scale height and faster rotation speed than either massive stars or the cold ISM. We investigate the origin of this discrepancy using an N-body + hydrodynamics simulation of a Milky-Way-like galaxy, self-consistently including self-gravity, star formation, stellar feedback, and 26Al production. We find no evidence that the Milky Way’s spiral structure explains the 26Al anomaly. Stars and the 26Al bubbles they produce form along spiral arms, but, because our simulation produces material arms that arise spontaneously rather than propagating arms forced by an external potential, star formation occurs at arm centres rather than leading edges. As a result, we find a scale height and rotation speed for 26Al similar to that of the cold ISM. However, we also show that a synthetic 26Al emission map produced for a possible Solar position at the edge of a large 26Al bubble recovers many of the major qualitative features of the observed 26Al sky. This suggests that the observed anomalous 26Al distribution is the product of foreground emission from the 26Al produced by a nearby, recent SN.

scholarly journals Large-scale galactic shock phenomena and the implications on star formation

1970 ◽  
Vol 38 ◽  
pp. 415-422
Author(s):  
W. W. Roberts
Keyword(s):  
Star Formation ◽  
Gravitational Collapse ◽  
Large Scale ◽  
Milky Way ◽  
Spiral Structure ◽  
Triggering Mechanism ◽  
Grand Design ◽  
Armed Spiral

The possible existence of a stationary two-armed spiral shock pattern for a disk-shaped galaxy, such as our own Milky Way System, is demonstrated. It is therefore suggested that large-scale galactic shock phenomena may very well form the large-scale triggering mechanism for the gravitational collapse of gas clouds, leading to star formation along narrow spiral arcs within a two-armed grand design of spiral structure.

scholarly journals Star Formation, Giant Hii Regions and Spiral Structure

1986 ◽  
Vol 7 ◽  
pp. 531-538
Author(s):  
Michael Rosa
Keyword(s):  
Star Formation ◽  
Title I ◽  
Spiral Structure ◽  
Hii Regions ◽  
Stellar Content ◽  
Recent Developments ◽  
Short Time

The three topics outlined in the title I have been given for this contribution are each far too complex to be thoroughly reviewed in the short time available. Instead of trying to duplicate the relevant (28, 34, 35) Commission Reports in the Transactions of the IAU (R.M. West 1985), I shall review only briefly current results on the stellar content of giant HII regions and then continue towards recent developments of our ideas about the mutual interrelation of galaxy wide star formation and spiral structure. The goal is to emphasize the simultaneous need for descriptions of details and unifying approaches.

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