scholarly journals How to Model the Chemical Evolution of Galaxies

1993 ◽  
Vol 155 ◽  
pp. 557-566
Author(s):  
Joachim Köppen
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Time Scale ◽  
Life Time ◽  
Magellanic Clouds ◽  
Formation Time ◽  
List Type ◽  
The Galaxy ◽  
H Ii Region ◽  
Magellanic Stream

For a first interpretation of the comparison of observational data, the crude “Simple Model” of chemical evolution is quite useful. Since it has well been described in the literature (e.g. Pagel and Patchett 1975, Tinsley 1980), let us here just review the assumptions and whether they are satisfied: 1.The galaxy is a closed system, with no exchange of matter with its surroundings: For the solar neighbourhood this probably is not true (the infamous Gdwarf-“problem”, Pagel 1989b). For the Magellanic Clouds this is most certainly wrong, because of the presence of the Inter-Cloud Region and the Magellanic Stream, and evidence for interaction with each other and the Galaxy as well (cf. e.g. Westerlund 1990).2.It initially consists entirely of gas (without loss of generality of primordial composition): This is good approximation also for models with gas infall, as long as the infall occurs with a time scale shorter than the star formation time scale.3.The metal production of the average stellar generation (the yield y) is constant with time: Initially, it is reasonable to make this assumption. For tables of the oxygen yield see Koppen and Arimoto (1991).4.The metal rich gas ejected by the stars is completely mixed with the ambient gas. To neglect the finite stellar life times (“instantaneous recycling approximation”) is appropriate for elements synthesized in stars whose life time is much shorter than the star formation time scale, such as oxygen, neon, sulphur, and argon.5.The gas is well mixed at all times: We don't know. The dispersion of H II region abundances may give an indication. In the Magellanic Clouds Dufour (1984) finds quite a low value (±0.08 dex for oyxgen).

scholarly journals Kinematics and Dynamics of the Magellanic Clouds

1984 ◽  
Vol 108 ◽  
pp. 107-114
Author(s):  
K. C. Freeman
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Magellanic Clouds ◽  
Star Formation History ◽  
Kinematics And Dynamics ◽  
List Type ◽  
Formation History ◽  
The Galaxy ◽  
History Of ◽  
Magellanic Stream

Why are the kinematics and dynamics of the Magellanic Clouds worth studying ? Some of the reasons are: 1.The Clouds are the closest examples of Magellanic systems. These asymmetric systems give some interesting dynamical problems. Because the Clouds are so close, a unique amount of information can be obtained on the kinematics of objects of all ages. This should be very helpful for understanding the dynamics.2.The Clouds and the Galaxy are interacting. This produces complex kinematics of the gas in and between the Clouds, and also the Magellanic Stream. Again, very detailed information can be derived. We would like to know enough about the gas dynamics of interacting galaxies, to be able to explain the kinematics produced by this interaction.3.The interaction will affect the star formation and chemical evolution in the Clouds. As new results are obtained on the star formation history and the chemical evolution, it is important to follow in parallel the dynamical history of the system, to see if the dynamics, star formation and chemical evolution can be tied together.

scholarly journals Michigan 160: a precursor to the LMC?

1991 ◽  
Vol 148 ◽  
pp. 376-377
Author(s):  
L. Staveley-Smith
Keyword(s):  
Star Formation ◽  
Dynamical Evolution ◽  
Stellar Populations ◽  
Detailed Comparison ◽  
Elliptical Galaxies ◽  
Magellanic Clouds ◽  
Formation Processes ◽  
Stellar Formation ◽  
The Galaxy ◽  
Magellanic Stream

The tidal interaction between the Magellanic Clouds and the Galaxy is an important factor in influencing the physical and dynamical evolution of the Clouds (e.g. the Magellanic Stream) as well as the genesis and evolution of their respective stellar populations. However, how important is the influence of the Galaxy? This is a key question since we know that relatively isolated, magellanic-type galaxies do exist (e.g. NGC 3109 and NGC 4449) and have been just as efficient at star-formation as the LMC. It is possible in fact that the star formation in the clouds is primarily stochastic in nature and is relatively insensitive to the global forces which seem to have shaped stellar formation processes in massive spiral and elliptical galaxies. Unsupported by a massive bulge or halo component, cold gas disks are inherently susceptible to radial and bar-like instabilities (Efstathiou et al. 1982) which are very efficient at creating the dynamical pressures required for rapid star-formation. With this in mind, a detailed comparison of 'field' magellanic-type galaxies with the LMC and SMC is of some importance.

scholarly journals Review of N-Body Models of Tidal Interactions

1999 ◽  
Vol 190 ◽  
pp. 480-486
Author(s):  
L. T. Gardiner
Keyword(s):  
Star Formation ◽  
Triple System ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Magellanic Clouds ◽  
Considerable Progress ◽  
Tidal Interactions ◽  
The Galaxy ◽  
Magellanic Stream ◽  
Made In

Considerable progress has been made in the current decade with the help of N-body simulations towards a deeper understanding of the nature of the dynamical relationship between the Large and Small Magellanic Clouds and the Galaxy. The origin of such features as the Magellanic Stream, the inter-Cloud Bridge, the Wing and large extension in depth of the SMC has come to be interpreted in the context of the tidal interactions among the members of the LMC-SMC-Galaxy triple system. The inclusion of gas-dynamical effects and star formation in the latest models has added further refinements to this picture and confirmed the enhancement of the star formation rate in the SMC as a result of the recent LMC-SMC encounter.

scholarly journals The chemical evolution of the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 367-369
Author(s):  
S. C. Russell
Keyword(s):  
Star Formation ◽  
Simple Model ◽  
Observational Data ◽  
Chemical Evolution ◽  
Structural Evolution ◽  
Star Clusters ◽  
Magellanic Clouds ◽  
Gas Content ◽  
The Galaxy ◽  
Simple Models

The chemical and structural evolution of the Magellanic Clouds are compared with those of the Galaxy. Simple models with gas infall and bimodal star formation are assumed, and are constrained by the most recent observational data. The evolution of the gas content, and the He, C, O and Fe abundances are all successfully modelled. The abundance of N is, however, predicted too high, and the apparent ages of the oldest star clusters are inconsistent with the simple model.

scholarly journals Photometric Studies of the Extreme SMC Wing

1980 ◽  
Vol 85 ◽  
pp. 353-355 ◽  
Author(s):  
William E. Kunkel
Keyword(s):  
Star Formation ◽  
Time Scales ◽  
Formation Time ◽  
Stellar Systems ◽  
Tidal Disruption ◽  
Tidal Interaction ◽  
Magellanic Stream

Among the currently interesting problems of interpreting the Magellanic Stream as an instance of tidal disruption is that of finding some demonstrable phenomenon in the makeup of the involved material that parallels the better known cases of tidal interaction, as for example NGC4038/39, where the dynamic and star-formation time scales are in agreement (Schweizer 1977). The observational problems that beset the interpretation of the Magellanic Stream are numerous (Mathewson and Schwartz 1976, Kunkel 1979, Bregman 1979), and the marked difference between the composition of the Stream (evidenced purely through HI) and the stellar systems (at least 80 percent stars) is among the outstanding dilemmas remaining. Finding some counterpart in the Magellanic scene comparable to the better recognized instances of tidal interaction may go some way towards clarifying a perplexing situation.

The Magellanic Clouds at Millimetre Wavelengths: A Brief Overview

1996 ◽  
Vol 13 (2) ◽  
pp. 187-188
Author(s):  
Lister Staveley-Smith
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Magellanic Clouds ◽  
Low Frequencies ◽  
The Galaxy ◽  
Compact Array

There are several excellent reasons for studying the Magellanic Clouds at millimetre wavelengths with a telescope such as the AT Mopra antenna:• The Magellanic Clouds are the nearest young, gas-rich galaxies to the Galaxy. They are therefore ideal places to study the processes which lead to star formation, and for comparing these processes with Galactic processes.• The distances of the Clouds are well established at close to 50 kpc for the LMC and 60 kpc for the SMC.• The Mopra beam at 2·6 mm (CO) corresponds to ~10 pc, which is comparable with the size of molecular clouds and complexes in the LMC and SMC (e.g. Rubio et al. 1993). The Mopra beam is also complementary to that obtainable at low frequencies with the AT Compact Array for continuum and HI studies (e.g. the 750 m configuration at 21 cm will give a resolution of ~12pc).

scholarly journals Massive Star Formation in W49

1987 ◽  
Vol 115 ◽  
pp. 143-145
Author(s):  
J. Dreher ◽  
S. Vogel ◽  
S. Terebey ◽  
W. J. Welch
Keyword(s):  
Star Formation ◽  
High Resolution ◽  
Massive Star ◽  
Hii Regions ◽  
Molecular Line ◽  
The Galaxy ◽  
Molecular Lines ◽  
H Ii Region ◽  
Scale Structures ◽  
The Continuum

W49 is the most luminous H II region complex in the galaxy. VLA maps in the continuum reveal a complex of more than two dozen compact HII regions, including a ring-like distribution of a dozen such regions within a volume of 1 pc. In addition to the VLA maps, we have obtained high resolution maps in this field with the Hat Creek Millimeter Interferometer in the following molecular lines: HCO+(1-0), H13CO+(1-0), SiO(v = 0, J = 2-1), SiO(v = 1, J = 2-1), H13CN(1-0), HC15N(1-0), SO2 [8(3,5)-9(2,8)], SO2[8(1,7)-8(0,8)], SO[2(2)-1(1)], and CH3CH2CN[10(1,10)-9(1,9)], all near 3 mm wavelengh. These maps will be discussed. The HCO+distribution corresponds to the larger scale structures observed in the continuum maps. In contrast the SO and SiO sources are quite compact. Using the detailed molecular line results obtained in the ORION/KL region as a guide, we are able to identify these latter sources as regions in which the star formation is at an earlier stage, regions where there are outflows.

scholarly journals Stochastic modelling of star-formation histories II: star-formation variability from molecular clouds and gas inflow

2020 ◽  
Vol 497 (1) ◽  
pp. 698-725 ◽  
Author(s):  
Sandro Tacchella ◽  
John C Forbes ◽  
Neven Caplar
Keyword(s):  
Life Cycle ◽  
Star Formation ◽  
Time Scales ◽  
Time Scale ◽  
Molecular Clouds ◽  
Star Formation History ◽  
Small Scale ◽  
Inflow Rate ◽  
Wide Range ◽  
The Galaxy

ABSTRACT A key uncertainty in galaxy evolution is the physics regulating star formation, ranging from small-scale processes related to the life-cycle of molecular clouds within galaxies to large-scale processes such as gas accretion on to galaxies. We study the imprint of such processes on the time-variability of star formation with an analytical approach tracking the gas mass of galaxies (‘regulator model’). Specifically, we quantify the strength of the fluctuation in the star-formation rate (SFR) on different time-scales, i.e. the power spectral density (PSD) of the star-formation history, and connect it to gas inflow and the life-cycle of molecular clouds. We show that in the general case the PSD of the SFR has three breaks, corresponding to the correlation time of the inflow rate, the equilibrium time-scale of the gas reservoir of the galaxy, and the average lifetime of individual molecular clouds. On long and intermediate time-scales (relative to the dynamical time-scale of the galaxy), the PSD is typically set by the variability of the inflow rate and the interplay between outflows and gas depletion. On short time-scales, the PSD shows an additional component related to the life-cycle of molecular clouds, which can be described by a damped random walk with a power-law slope of β ≈ 2 at high frequencies with a break near the average cloud lifetime. We discuss star-formation ‘burstiness’ in a wide range of galaxy regimes, study the evolution of galaxies about the main sequence ridgeline, and explore the applicability of our method for understanding the star-formation process on cloud-scale from galaxy-integrated measurements.

scholarly journals Chemical Evolution of the Galactic Disk and Bulge

1995 ◽  
Vol 164 ◽  
pp. 133-149
Author(s):  
Rosemary F.G. Wyse
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Milky Way ◽  
Galactic Disk ◽  
Mass Function ◽  
Initial Mass Function ◽  
List Type ◽  
Dark Halo ◽  
Milky Way Galaxy ◽  
The Galaxy

The Milky Way Galaxy offers a unique opportunity for testing theories of galaxy formation and evolution. The study of the spatial distribution, kinematics and chemical abundances of stars in the Milky Way Galaxy allows one to address specific questions pertinent to this meeting such as (i)When was the Galaxy assembled? Is this an ongoing process? What was the merging history of the Milky Way?(ii)When did star formation occur in what is now “The Milky Way Galaxy”? Where did the star formation occur then? What was the stellar Initial Mass Function?(iii)How much dissipation of energy was there before and during the formation of the different stellar components of the Galaxy?(iv)What are the relationships among the different stellar components of the Galaxy?(v)Was angular momentum conserved during formation of the disk(s) of the Galaxy?(vi)What is the shape of the dark halo?(vii)Is there dissipative (disk) dark matter?

Sign in / Sign up

Export Citation Format

Share Document