Surviving infant mortality in the hierarchical merging scenario

Smith, Rory; Fellhauer, M.; Goodwin, S. P.; Assmann, P.

doi:10.1111/j.1365-2966.2011.18604.x

Cited by 60 publications

(86 citation statements)

References 40 publications

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“…This agrees with observations that find typical SFEs in the solar neighbourhood to lie in the range of 0.1 < SFE < 0.35 (Lada 1999;Lada & Lada 2003). For an alternative explanation for the high cluster infant mortality see Smith et al (2011).…”

Section: Introductionsupporting

confidence: 81%

Reaction of massive clusters to gas expulsion – The cluster density dependence

Pfalzner

Kaczmarek

2013

A&A

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Context. The expulsion of the unconverted gas at the end of the star formation process potentially leads to the expansion of the just formed stellar cluster and membership loss. The degree of expansion and mass loss depends largely on the star formation efficiency and scales with the mass and size of the stellar group when stellar interactions can be neglected. Aims. We investigate the circumstances in which stellar interactions between cluster members become so important that the fraction of bound stars after gas expulsion is significantly altered. Methods. The Nbody6 code is used to simulate the cluster dynamics after gas expulsion for different star formation efficiences. Concentrating on the most massive clusters observed in the Milky Way, we test to what extent the results depend on the model, i.e. stellar mass distribution, stellar density profile etc., and the cluster parameters, such as cluster density and size. Results. We find that stellar interactions leading to ejections are responsible for up to 20% mass loss in the most compact massive clusters in the Milky Way. Therefore, ejections are the prime mass loss process in these systems. Even in the loosely bound OB associations, stellar interactions are responsible for at least ∼5% mass loss. The main reason why the importance of encounters for massive clusters has been largely overlooked is because of the often used approach of a single-mass representation instead of a realistic distribution for the stellar masses. The density dependence on the encounter-induced mass loss is shallower than expected because of the increasing importance of few-body interactions in dense clusters compared to sparse clusters where 2-body encounters dominate.

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Section: Introductionsupporting

confidence: 81%

Reaction of massive clusters to gas expulsion – The cluster density dependence

Pfalzner

Kaczmarek

2013

A&A

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“…For the SFE, a critical value for forming a remnant cluster is somewhere between 10% and 35%; the lower value corresponding to systems with slow gas expulsion and/or sub-clustered structures, and the higher value to instantaneous gas expulsion and smoothly distributed systems. The current picture, suggested by simulations, can be summarised as: a bound cluster is more likely to form if the SFE is high, the time scale of gas removal is long, and/or the system begins in a sub-virial state (e.g., McMillan et al 2007;Allison et al 2009;Goodwin 2009;Smith et al 2011). For a more detailed review of existing theoretical and numerical work, we refer to the accompanying paper (Pfalzner & Kaczmarek 2013, hereafter Paper I).…”

Section: Introductionmentioning

confidence: 99%

The expansion of massive young star clusters – observation meets theory

Pfalzner¹,

Kaczmarek²

2013

A&A

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Context. Most stars form as part of a star cluster. The most massive clusters in the Milky Way exist in two groups -loose and compact clusters -with significantly different sizes at the end of the star formation process. After their formation, both types of clusters expand up to a factor 10-20 within the first 20 Myr of their development. Gas expulsion at the end of the star formation process is usually regarded as the only possible process that can lead to such an expansion during this early period of development. Aims. We investigate the effect of gas expulsion by a direct comparison between numerical models and observed clusters and concentrate on clusters with masses >10 3 M . For these clusters the initial conditions before gas expulsion, the characteristic cluster development, its dependence on cluster mass, and the star formation efficiency (SFE) are investigated. Methods. We performed N-body simulations of the cluster expansion process after gas expulsion and compared the results with observations. Results. We find that the expansion processes of the observed loose and compact massive clusters are driven by completely different physical processes. As expected, the expansion of loose massive clusters is largely driven by the gas loss due to the low SFE of ∼30%. One new revelation is that all the observed massive clusters of this group seem to have a very similar size of 1-3 pc at the onset of expansion. It is demonstrated that compact clusters have a much higher effective SFE of 60-70% and are as a result much less affected by gas expulsion. Their expansion is mainly driven by stellar ejections caused by interactions between the cluster members. The reason ejections are so efficient in driving cluster expansion is that they occur dominantly from the cluster centre and over an extended period of time. During the first 10 Myr the internal dynamics of loose and compact clusters thus differ fundamentally.

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“…These observations are associated with program 10248. dispersal phase depends largely on the efficiency of star formation (SF), a property that is still poorly quantified (Elmegreen 2007;Price & Bate 2009). Recently, Smith et al (2011) have studied the effects of gas expulsion on sub-structured clusters formed under non-equilibrium initial conditions. They find that the initial spatial and kinematic distributions of the stars are far more important for cluster survival than the SF efficiency.…”

Section: Introductionmentioning

confidence: 99%

Is the Young Star Cluster NGC 376 Dissolving in the Field of the Small Magellanic Cloud?

Sabbi

Nota

Tosi

et al. 2011

ApJ

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We use deep images acquired with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope in the filters F555W and F814W to characterize the properties of NGC 376, a young star cluster located in the wing of the Small Magellanic Cloud. Using isochrone fitting we derive for NGC 376 an age of 28 ± 7 Myr, in good agreement with previous studies. The high spatial resolution ACS data allow us to determine the center of gravity of the cluster and to construct extended surface brightness and radial density profiles. Neither of these profiles can be fitted with a theoretical model, suggesting that the cluster is not in virial equilibrium. Considering the young age of the cluster, we speculate that the distortion of the radial profiles may be the result of the rapid gas dispersal that follows the initial phase of star formation (SF). The cluster shows clear evidence of dynamical mass segregation. From the properties of the radial profiles and the present-day mass function we conclude that NGC 376 appears to have already lost nearly 90% of its initial stellar mass, probably as a consequence of the sudden gas dispersal that follows the early phase of SF.

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Surviving infant mortality in the hierarchical merging scenario

Cited by 60 publications

References 40 publications

Reaction of massive clusters to gas expulsion – The cluster density dependence

Reaction of massive clusters to gas expulsion – The cluster density dependence

The expansion of massive young star clusters – observation meets theory

Is the Young Star Cluster NGC 376 Dissolving in the Field of the Small Magellanic Cloud?

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