The global mass functions of 35 Galactic globular clusters: I. Observational data and correlations with cluster parameters

Sollima, A.; Baumgardt, Holger

doi:10.1093/mnras/stx1856

Cited by 75 publications

(70 citation statements)

References 67 publications

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“…We also include data from Baumgardt & Hilker (2018) but we limit the sample to bright GCs with M V < −7.5 and those with a mass function slope of α < −0.8. This eliminates clusters that have evolved strongly from the initial Kroupa mass funtion (Sollima & Baumgardt 2017); the remaining sample of dynamically unevolved clusters provides a good match to the high mass, long relaxation time UCDs. Sollima & Baumgardt (2017) found a strong correlation between mass function slope and relaxation time of a cluster.…”

Section: Empirical Ml-metallicity Relationmentioning

confidence: 99%

The Impact of Stripped Nuclei on the Supermassive Black Hole Number Density in the Local Universe

Voggel

Seth

Baumgardt

et al. 2019

ApJ

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The recent discovery of super-massive black holes (SMBHs) in high-mass ultra-compact dwarf galaxies (UCDs) suggests that at least some UCDs are the nuclear star clusters of stripped galaxies. In this paper we present a new method to estimate how many UCDs host an SMBH and thus are stripped galaxy nuclei. We revisit the dynamical mass measurements that suggest many UCDs have more mass than expected from stellar population estimates, which observations have shown is due to the presence of an SMBH. We revise the stellar population mass estimates using a new empirical relation between the mass-to-light ratio (M/L) and metallicity to predict which UCDs most likely host an SMBH. We calculate the fraction of UCDs that host SMBHs across their entire luminosity range for the first time. We then apply the SMBH occupation fraction to the observed luminosity function of UCDs and estimate that in the Fornax and Virgo cluster alone there should be 69 +32 −25 stripped nuclei with SMBHs. This analysis shows that stripped nuclei are almost as common in clusters as present-day galaxy nuclei. We estimate the SMBH number density caused by stripped nuclei to be 2 − 8 × 10 −3 M pc −3 , which represents a significant fraction (8-32%) of the SMBH density in the local Universe. These SMBHs hidden in stripped nuclei increase expected event rates for tidal disruption events and SMBH-SMBH and SMBH-BH mergers. The existence of numerous stripped nuclei with SMBHs are a direct consequence of hierarchical galaxy formation, but until now their impact on the SMBH density had not been quantified.

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Section: Empirical Ml-metallicity Relationmentioning

confidence: 99%

The Impact of Stripped Nuclei on the Supermassive Black Hole Number Density in the Local Universe

Voggel

Seth

Baumgardt

et al. 2019

ApJ

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“…To convert magnitudes to stellar masses, they adopted the mass-luminosity relation of suitable isochrones from the Dotter et al (2007) database. 47 Tuc was not retained in the final sample analysed in Sollima & Baumgardt (2017), but stellar mass functions determined in the same way as for their 35 selected clusters were provided to us by A. Sollima (priv.…”

Section: Stellar Mass Functionsmentioning

confidence: 99%

“…In fact, dynamical Monte Carlo of models of 47 Tuc require a flat (low-mass) IMF as initial conditions to reproduce a flat present-day mass function (Giersz & Heggie 2011). Other GCs with similar t rh tend to have steeper low-mass mass functions (corresponding to α 1 indices of ∼ 1, Sollima & Baumgardt 2017, their figure 3), making 47 Tuc a clear outlier. Fig.…”

Section: The Initial Stellar Mass Functionmentioning

confidence: 99%

On the black hole content and initial mass function of 47 Tuc

Hénault-Brunet

Gieles

Strader

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The globular cluster (GC) 47 Tuc has recently been proposed to host an intermediate-mass black hole (IMBH) or a population of stellar-mass black holes (BHs). To shed light on its dark content, we present an application of self-consistent multimass models with a varying mass function and content of stellar remnants, which we fit to various observational constraints. Our best-fitting model successfully matches the observables and correctly predicts the radial distribution of millisecond pulsars and their gravitational accelerations inferred from longterm timing observations. The data favours a population of BHs with a total mass of 430 +386 −301 M , but the most likely model has very few BHs. Since our models do not include a central IMBH and accurately reproduce the observations, we conclude that there is currently no need to invoke the presence of an IMBH in 47 Tuc. The global present-day mass function inferred is significantly depleted in low-mass stars (power-law slope α = −0.52 +0.17 −0.16 ). Given the orbit and predicted mass-loss history of this massive GC, the dearth of low-mass stars is difficult to explain with a standard initial mass function (IMF) followed by long-term preferential escape of low-mass stars driven by two-body relaxation, and instead suggests that 47 Tuc may have formed with a bottom-light IMF. We discuss alternative evolutionary origins for the flat mass function and ways to reconcile this with the low BH retention fraction. Finally, by capturing the effect of dark remnants, our method offers a new way to probe the IMF in a GC above the current main-sequence turn-off mass, for which we find a slope of −2.49 ± 0.08.

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“…Present-day mass function slope. There exists a strong correlation between the stellar mass function (MF) of a GC and the amount of mass lost from the cluster as well as their relaxation time (Sollima & Baumgardt 2017, Baumgardt & Hilker 2018. Both, metalrich and metal-poor GGCs, follow the same correlation.…”

Section: Some Key Resultsmentioning

confidence: 99%

Galactic Globular Clusters: A new catalog of masses, structural parameters, velocity dispersion profiles, proper motions and space orbits

et al. 2019

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We collected radial velocities of more than 50.000 individual stars in 156 Galactic globular clusters (GGC) and matched them with HST photometry and Gaia DR2 proper motions. This allowed us to derive the GGC's mean proper motions and space velocities. By fitting a large set of N-body simulations to their velocity dispersion and surface density profiles, combined with new measurements of their internal radially dependent mass functions, we have determined their present-day masses and structural parameters, and for 144 GGCs their internal kinematics. We also derive the initial cluster masses by calculating the cluster orbits backwards in time applying suitable recipes to account for mass-loss and dynamical friction. The new fundamental parameters of GGCs are publicly available via an online database, which will regularly be updated.

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The global mass functions of 35 Galactic globular clusters: I. Observational data and correlations with cluster parameters

Cited by 75 publications

References 67 publications

The Impact of Stripped Nuclei on the Supermassive Black Hole Number Density in the Local Universe

The Impact of Stripped Nuclei on the Supermassive Black Hole Number Density in the Local Universe

On the black hole content and initial mass function of 47 Tuc

Galactic Globular Clusters: A new catalog of masses, structural parameters, velocity dispersion profiles, proper motions and space orbits

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