The Magellanic Clouds at Millimetre Wavelengths: A Brief Overview

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).

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The global star formation law: from dense cores to extreme starbursts

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307001688 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 331-335

Author(s):

Yu Gao

Keyword(s):

Star Formation ◽

Linear Correlation ◽

Molecular Clouds ◽

High Redshift ◽

Gas Content ◽

Molecular Gas ◽

Giant Molecular Clouds ◽

Active Star ◽

Dense Cores ◽

The Galaxy

AbstractActive star formation (SF) is tightly related to the dense molecular gas in the giant molecular clouds' dense cores. Our HCN (measure of the dense molecular gas) survey in 65 galaxies (including 10 ultraluminous galaxies) reveals a tight linear correlation between HCN and IR (SF rate) luminosities, whereas the correlation between IR and CO (measure of the total molecular gas) luminosities is nonlinear. This suggests that the global SF rate depends more intimately upon the amount of dense molecular gas than the total molecular gas content. This linear relationship extends to both the dense cores in the Galaxy and the hyperluminous extreme starbursts at high-redshift. Therefore, the global SF law in dense gas appears to be linear all the way from dense cores to extreme starbursts, spanning over nine orders of magnitude in IR luminosity.

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Molecular Clouds and Star Formation at Large R

Symposium - International Astronomical Union ◽

10.1017/s0074180900088987 ◽

1991 ◽

Vol 144 ◽

pp. 121-130

Author(s):

J. Brand ◽

J.G.A. Wouterloot

Keyword(s):

Star Formation ◽

Molecular Clouds ◽

Density Wave ◽

Cosmic Ray ◽

Volume Density ◽

Kinetic Temperature ◽

Galactocentric Distance ◽

The Galaxy ◽

The Mean ◽

Cosmic Ray Flux

In the outer Galaxy (defined here as those parts of our system with galactocentric radii R>R0) the HI gas density (Wouterloot et al., 1990), the cosmic ray flux (Bloemen et al, 1984) and the metallicity (Shaver et al., 1983) are lower than in the inner parts. Also, the effect of a spiral density wave is much reduced in the outer parts of the Galaxy due to corotation. This changing environment might be expected to have its influence on the formation of molecular clouds and on star formation within them. In fact, some differences with respect to the inner Galaxy have been found: the ratio of HI to H2 surface density is increasing from about 5 near the Sun to about 100 at R≈20kpc (Wouterloot et al., 1990). Because of the “flaring” of the gaseous disk, the scale height of both the atomic and the molecular gas increases by about a factor of 3 between R0 and 2R0 (Wouterloot et al., 1990), so the mean volume density of both constituents decreases even more rapidly than their surface densities. The size of HII regions decreases significantly with increasing galactocentric distance (Fich and Blitz, 1984), probably due to the fact that outer Galaxy clouds are less massive (see section 3.3), and therefore form fewer O-type stars than their inner Galaxy counter parts. There are indications that the cloud kinetic temperature is lower by a few degrees (Mead and Kutner, 1988), although it is not clear to what extent this is caused by beam dilution.

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How to Model the Chemical Evolution of Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900172407 ◽

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).

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Michigan 160: a precursor to the LMC?

Symposium - International Astronomical Union ◽

10.1017/s0074180900200910 ◽

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.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1838 ◽

2020 ◽

Vol 497 (1) ◽

pp. 698-725 ◽

Cited By ~ 3

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.

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Chemical Abundances and Isotope Ratios in Molecular Clouds

Publications of the Astronomical Society of Australia ◽

10.1017/s132335800002083x ◽

1996 ◽

Vol 13 (2) ◽

pp. 202-203

Author(s):

M. R. Hunt

Keyword(s):

Observational Data ◽

Molecular Clouds ◽

Isotope Ratios ◽

Magellanic Clouds ◽

Chemical Abundances ◽

Millimetre Wave ◽

The Galaxy ◽

Molecular Abundances

AbstractA program to observe millimetre-wave molecular transitions in a number of southern-sky molecular clouds is under way. Molecular clouds in both the Galaxy and the Magellanic Clouds are included in the sample. The aim of the program is to build a body of observational data which can be used to derive molecular abundances in southern-sky molecular clouds.

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Properties of star forming regions in the Magellanic Clouds

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308028470 ◽

2008 ◽

Vol 4 (S256) ◽

pp. 215-226

Author(s):

Mónica Rubio

Keyword(s):

Star Formation ◽

Galaxy Evolution ◽

Molecular Clouds ◽

Massive Star ◽

High Sensitivity ◽

Magellanic Clouds ◽

Molecular Gas ◽

Star Forming ◽

Star Forming Regions ◽

Low Metallicity

AbstractUnderstanding the process of star formation in low metallicity systems is one of the key studies in the early stages of galaxy evolution. The Magellanic Clouds, being the nearest examples of low metallicity systems, allow us to study in detail their star forming regions. As a consequence of their proximity we can resolve the molecular clouds and the regions of star formation individually. Therefore we can increase our knowledge of the interaction of young luminous stars with their environment. We will present results of multiwavelenghts studies of LMC and SMC massive star forming regions, which includes properties of the cold molecular gas, the embedded young population associated with molecular clouds, and the interaction of newly born stars with the surrounding interstellar medium, based on ASTE and APEX submillimeter observations complemented high sensitivity NIR groud based observations and Spitzer results.

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