Nuclear star clusters
- PDF / 18,357,744 Bytes
- 75 Pages / 439.37 x 666.142 pts Page_size
- 48 Downloads / 179 Views
Nuclear star clusters Nadine Neumayer1 · Anil Seth2 · Torsten Böker3 Received: 13 December 2019 © The Author(s) 2020
Abstract We review the current knowledge about nuclear star clusters (NSCs), and the spectacularly dense and massive assemblies of stars found at the centers of most galaxies. Recent observational and theoretical works suggest that many NSC properties, including their masses, densities, and stellar populations, vary with the properties of their host galaxies. Understanding the formation, growth, and ultimate fate of NSCs, therefore, is crucial for a complete picture of galaxy evolution. Throughout the review, we attempt to combine and distill the available evidence into a coherent picture of NSC evolution. Combined, this evidence points to a clear transition mass in galaxies of ∼ 109 M⊙ where the characteristics of nuclear star clusters change. We argue that at lower masses, NSCs are formed primarily from globular clusters that inspiral into the center of the galaxy, while at higher masses, star formation within the nucleus forms the bulk of the NSC. We also discuss the co-existence of NSCs and central black holes, and how their growth may be linked. The extreme densities of NSCs and their interaction with massive black holes lead to a wide range of unique phenomena including tidal disruption and gravitational-wave events. Finally, we review the evidence that many NSCs end up in the halos of massive galaxies stripped of the stars that surrounded them, thus providing valuable tracers of the galaxies’ accretion histories.
* Nadine Neumayer [email protected] Anil Seth [email protected] Torsten Böker [email protected] 1
Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
2
Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, UT 84112, USA
3
European Space Agency, c/o STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA
13
Vol.:(0123456789)
4
Page 2 of 75
N. Neumayer et al.
Contents 1 1 Introduction 2 2 Early studies 2.1 Imaging nuclear star clusters: the Hubble Space Telescope 2.2 Ground-based spectroscopic observations 2.3 Early theoretical studies 3 What is a nuclear star cluster? 4 Nuclear star cluster demographics 4.1 Trends with host galaxy mass, morphology, and color 4.2 Trends with host galaxy environment 5 Properties of nuclear star clusters 5.1 Sizes and morphologies 5.2 Luminosities and stellar masses 5.3 Size--mass relation and stellar densities 5.4 Stellar ages and metallicities 5.5 Kinematics of NSCs 5.6 Properties of the Milky Way nuclear star cluster 5.7 Properties of the M 31 nuclear star cluster 6 Nuclear star clusters and their host galaxies 6.1 Scaling relations of NSCs 6.2 Other correlations between NSCs and their hosts 7 Scenarios for the formation and growth of nuclear star clusters 7.1 Initial formation of NSCs 7.2 Globular cluster infall and merging 7.3 In situ star formation 7.4 NSC formation: different galaxies and different mechanisms 8 Nuclear star clusters and massive black holes
Data Loading...
