Lithium Abundances, Diffusion and Macroscopic Motions in Stellar Clusters

The ecology of the galactic centre: Nuclear stellar clusters and supermassive black holes

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319006689 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 80-83 ◽

Cited By ~ 1

Author(s):

Melvyn B. Davies ◽

Abbas Askar ◽

Ross P. Church

Keyword(s):

Black Holes ◽

Black Hole ◽

Large Fraction ◽

Galactic Nuclei ◽

Supermassive Black Holes ◽

Galactic Centre ◽

Stellar Clusters ◽

Stellar Cluster ◽

Supermassive Black Hole ◽

Multiple Clusters

AbstractSupermassive black holes are found in most galactic nuclei. A large fraction of these nuclei also contain a nuclear stellar cluster surrounding the black hole. Here we consider the idea that the nuclear stellar cluster formed first and that the supermassive black hole grew later. In particular we consider the merger of three stellar clusters to form a nuclear stellar cluster, where some of these clusters contain a single intermediate-mass black hole (IMBH). In the cases where multiple clusters contain IMBHs, we discuss whether the black holes are likely to merge and whether such mergers are likely to result in the ejection of the merged black hole from the nuclear stellar cluster. In some cases, no supermassive black hole will form as any merger product is not retained. This is a natural pathway to explain those galactic nuclei that contain a nuclear stellar cluster but apparently lack a supermassive black hole; M33 being a nearby example. Alternatively, if an IMBH merger product is retained within the nuclear stellar cluster, it may subsequently grow, e.g. via the tidal disruption of stars, to form a supermassive black hole.

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The effect of photoionizing feedback on the shaping of hierarchically-forming stellar clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2921 ◽

2020 ◽

Vol 499 (1) ◽

pp. 668-680

Author(s):

Alejandro González-Samaniego ◽

Enrique Vazquez-Semadeni

Keyword(s):

Star Formation ◽

Early Stage ◽

Stellar Clusters ◽

Low Mass Stars ◽

Transfer Scheme ◽

Star Forming ◽

Secondary Star ◽

Low Mass ◽

Hydrodynamical Simulations ◽

Formation Efficiency

ABSTRACT We use two hydrodynamical simulations (with and without photoionizing feedback) of the self-consistent evolution of molecular clouds (MCs) undergoing global hierarchical collapse (GHC), to study the effect of the feedback on the structural and kinematic properties of the gas and the stellar clusters formed in the clouds. During this early stage, the evolution of the two simulations is very similar (implying that the feedback from low-mass stars does not affect the cloud-scale evolution significantly) and the star-forming region accretes faster than it can convert gas into stars, causing the instantaneous measured star formation efficiency (SFE) to remain low even in the absence of significant feedback. Afterwards, the ionizing feedback first destroys the filamentary supply to star-forming hubs and ultimately removes the gas from it, thus first reducing the star formation (SF) and finally halting it. The ionizing feedback also affects the initial kinematics and spatial distribution of the forming stars because the gas being dispersed continues to form stars, which inherit its motion. In the non-feedback simulation, the groups remain highly compact and do not mix, while in the run with feedback, the gas dispersal causes each group to expand, and the cluster expansion thus consists of the combined expansion of the groups. Most secondary star-forming sites around the main hub are also present in the non-feedback run, implying a primordial rather than triggered nature. We do find one example of a peripheral star-forming site that appears only in the feedback run, thus having a triggered origin. However, this appears to be the exception rather than the rule, although this may be an artefact of our simplified radiative transfer scheme.

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Structure of the Milky Way and the distribution of young stellar clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307008083 ◽

2006 ◽

Vol 2 (S241) ◽

Author(s):

Maria Messineo ◽

Karl M. Menten ◽

Harm J. Habing ◽

Monika Petr-Gotzens ◽

Frédéric Schuller

Keyword(s):

Milky Way ◽

Stellar Clusters

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Formation of supermassive black holes in galactic nuclei – I. Delivering seed intermediate-mass black holes in massive stellar clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab113 ◽

2021 ◽

Vol 502 (2) ◽

pp. 2682-2700

Author(s):

Abbas Askar ◽

Melvyn B Davies ◽

Ross P Church

Keyword(s):

Black Holes ◽

Galactic Nuclei ◽

Supermassive Black Holes ◽

Stellar Clusters ◽

Orbital Eccentricity ◽

Intermediate Mass ◽

Stellar Cluster ◽

Wave Emission ◽

Gas Accretion ◽

Intermediate Mass Black Holes

ABSTRACT Supermassive black holes (SMBHs) are found in most galactic nuclei. A significant fraction of these nuclei also contains a nuclear stellar cluster (NSC) surrounding the SMBH. In this paper, we consider the idea that the NSC forms first, from the merger of several stellar clusters that may contain intermediate-mass black holes (IMBHs). These IMBHs can subsequently grow in the NSC and form an SMBH. We carry out N-body simulations of the simultaneous merger of three stellar clusters to form an NSC, and investigate the outcome of simulated runs containing zero, one, two, and three IMBHs. We find that IMBHs can efficiently sink to the centre of the merged cluster. If multiple merging clusters contain an IMBH, we find that an IMBH binary is likely to form and subsequently merge by gravitational wave emission. We show that these mergers are catalyzed by dynamical interactions with surrounding stars, which systematically harden the binary and increase its orbital eccentricity. The seed SMBH will be ejected from the NSC by the recoil kick produced when two IMBHs merge, if their mass ratio q ≳ 0.15. If the seed is ejected then no SMBH will form in the NSC. This is a natural pathway to explain those galactic nuclei that contain an NSC but apparently lack an SMBH, such as M33. However, if an IMBH is retained then it can seed the growth of an SMBH through gas accretion and tidal disruption of stars.

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The IMF of stellar clusters: effects of accretion and feedback

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2010.16451.x ◽

2010 ◽

Cited By ~ 8

Author(s):

Sami Dib ◽

Mohsen Shadmehri ◽

Paolo Padoan ◽

G. Maheswar ◽

D. K. Ojha ◽

...

Keyword(s):

Stellar Clusters ◽

The Imf

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Internal Structure of Stellar Clusters: Geometry of Star Formation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311000214 ◽

2010 ◽

Vol 6 (S270) ◽

pp. 81-88

Author(s):

Emilio J. Alfaro ◽

Néstor Sánchez

Keyword(s):

Internal Structure ◽

Dynamical Evolution ◽

Direct Consequence ◽

Open Clusters ◽

Condensed State ◽

Stellar Clusters ◽

Early Effect ◽

Fractal Medium ◽

Fractal Patterns ◽

Simple Picture

AbstractThe study of the internal structure of star clusters provides important clues concerning their formation mechanism and dynamical evolution. There are both observational and numerical evidences indicating that open clusters evolve from an initial clumpy structure, presumably a direct consequence of the formation in a fractal medium, toward a centrally condensed state. This simple picture has, however, several drawbacks. There can be very young clusters exhibiting radial patterns maybe reflecting the early effect of gravity on primordial gas. There can be also very evolved clusters showing fractal patterns that either have survived through time or have been generated subsequently by some (unknown) mechanism. Additionally, the fractal structure of some open clusters is much clumpier than the average structure of the interstellar medium in the Milky Way, although in principle a very similar structure should be expected. Here we summarize and discuss observational and numerical results concerning this subject.

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A13CO and C18O Survey of the Molecular Gas Around Young Stellar Clusters within 1 Kiloparsec of the Sun

The Astronomical Journal ◽

10.1086/375455 ◽

2003 ◽

Vol 126 (1) ◽

pp. 286-310 ◽

Cited By ~ 64

Author(s):

Naomi A. Ridge ◽

T. L. Wilson ◽

S. T. Megeath ◽

L. E. Allen ◽

P. C. Myers

Keyword(s):

Molecular Gas ◽

The Sun ◽

Stellar Clusters

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Further developments in star cluster spectral libraries

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309991244 ◽

2009 ◽

Vol 5 (S266) ◽

pp. 347-350

Author(s):

Andrea V. Ahumada ◽

Juan J. Clariá ◽

Eduardo Bica ◽

Andrés E. Piatti ◽

João F. C. Santos ◽

...

Keyword(s):

Spectral Range ◽

Equivalent Width ◽

Template Matching ◽

Magellanic Cloud ◽

Star Cluster ◽

Open Clusters ◽

Stellar Clusters ◽

Colour Excess ◽

Matching Procedure ◽

Spectral Libraries

AbstractWe present flux-calibrated integrated spectra in the optical spectral range of Galactic open clusters (GOCs) and Magellanic Cloud (MC) stellar clusters (SCs) obtained at CASLEO (Argentina). The SC parameters were derived using the equivalent-width (EW) method and the template-matching procedure by comparing the line strengths and continuum distribution of the cluster spectra with those of template spectra with known parameters. MC cluster reddening values were also estimated by interpolation between the available extinction maps. The derived ages for the GOCs range from 3 Myr to 4 Gyr, while those of the MC SCs vary from 3 Myr to 7 Gyr. E(B−V) colour-excess values in the MCs appear to be all lower than 0.17 mag, while those of the GOCs range from 0.00 to 2.40 mag. The present data led us to upgrade the spectral libraries of reference spectra or templates of solar and MC metallicities.

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