The Orbits of 48 Globular Clusters in a Milky Way–like Barred Galaxy

Allen, Christine; Moreno, E.; Pichardo, B.

doi:10.1086/508676

Cited by 78 publications

(140 citation statements)

References 35 publications

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“…Our study cannot be based on statistically assigned orbits but requires the actual orbits of individual clusters, thus excluding the estimated orbits from Gnedin & Ostriker (1997). In addition, the Dinescu et al (1999) destruction rates seem to be in better agreement with the observations than those from Allen et al (2006Allen et al ( , 2008.…”

Section: Introductionmentioning

confidence: 70%

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Dissolution is the solution: on the reduced mass-to-light ratios of Galactic globular clusters

Kruijssen

Mieske²

2009

A&A

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Context. The observed dynamical mass-to-light (M/L) ratios of globular clusters (GCs) are systematically lower than the value expected from "canonical" simple stellar population models, which do not account for dynamical effects such as the preferential loss of low-mass stars due to energy equipartition. It has recently been shown that low-mass star depletion can qualitatively explain this discrepancy for globular clusters in several galaxies. Aims. To verify whether low-mass star depletion is indeed the driving mechanism behind the M/L decrease, we aim to predict the M/L V ratios of individual GCs for which orbital parameters and dynamical V-band mass-to-light ratios M/L V are known. There is a sample of 24 Galactic GCs for which this is possible. Methods. We used the SPACE cluster models, which include dynamical dissolution, low-mass star depletion, stellar evolution, stellar remnants, and various metallicities. We derived the dissolution timescales due to two-body relaxation and disc shocking from the orbital parameters of our GC sample and used these to predict the M/L V ratios of the individual GCs. To verify our findings, we also predicted the slopes of their low-mass stellar mass functions. Results. The computed dissolution timescales agree well with earlier empirical studies. The predicted M/L V are in 1σ agreement with the observations for 12 out of 24 GCs. The discrepancy for the other GCs probably arises because our predictions give global M/L ratios, while the observations represent extrapolated central values that are different from global ones in the case of mass segregation and a long dissolution timescale. The GCs in our sample that likely have dissimilar global and central M/L ratios can be excluded by imposing limits on the dissolution timescale and King parameter. For the remaining GCs, the observed and predicted average M/L V are 78 +9 −11 % and 78 ± 2% of the canonically expected values, while the values are 74 +6 −7 % and 85 ± 1% for the entire sample. The predicted correlation between the slope of the low-mass stellar mass function and M/L V drop is found to be qualitatively consistent with observed mass function slopes. Conclusions. The dissolution timescales of Galactic GCs are such that the ∼20% gap between canonically expected and observed M/L V ratios is bridged by accounting for the preferential loss of low-mass stars, also when considering individual clusters. It is concluded that the variation in M/L ratio due to dissolution and low-mass star depletion is a plausible explanation for the discrepancy between the observed and canonically expected M/L ratios of GCs.

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Section: Introductionmentioning

confidence: 70%

“…We are grateful to Dana Casetti-Dinescu for interesting discussions and for providing the disc shocking destruction rates from Dinescu et al (1999). Christine Allen is acknowledged for providing the data from Allen et al (2006Allen et al ( , 2008 …”

mentioning

confidence: 99%

Dissolution is the solution: on the reduced mass-to-light ratios of Galactic globular clusters

Kruijssen

Mieske²

2009

A&A

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“…With the alternative Eq. (1) in Allen et al (2006) the tidal radius is 8 pc. Both results are near the 9.6 pc value listed by Piskunov et al (2008).…”

Section: The Galactic Orbit Of M 67mentioning

confidence: 97%

Absolute proper motion of the Galactic open cluster M 67

Bellini

Bedin

Pichardo

et al. 2010

A&A

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We derived the absolute proper motion (PM) of the old, solar-metallicity Galactic open cluster M 67 using observations collected with CFHT (1997) and with LBT (2007). About 50 galaxies with relatively sharp nuclei allow us to determine the absolute PM of the cluster. We find (μ α cos δ, μ δ ) J2000.0 = (−9.6 ± 1.1, −3.7 ± 0.8) mas yr −1 . By adopting a line-of-sight velocity of 33.78 ± 0.18 km s −1 , and assuming a distance of 815 ± 50 pc, we explore the influence of the Galactic potential, with and without the bar and/or spiral arms, on the galactic orbit of the cluster.

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“…We did not include a barred potential, since its effect on the orbit of Pal 5 has been shown to be negligible (Allen et al 2006).…”

Section: Globular Cluster and Galaxy Modelsmentioning

confidence: 99%

Clumpy streams in a smooth dark halo: the case of Palomar 5

Mastrobuono-Battisti

Matteo

Montuori

et al. 2012

A&A

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By means of direct N-body simulations and simplified numerical models, we study the formation and characteristics of the tidal tails around Palomar 5, along its orbit in the Milky Way potential. Unlike previous findings, we are able to reproduce the substructures observed in the stellar streams of this cluster, without including any lumpiness in the dark matter halo. We show that overdensities similar to those observed in Palomar 5 can be reproduced by the epicyclic motion of stars along its tails, i.e. a simple local accumulation of orbits of stars that escaped from the cluster with very similar positions and velocities. This process is able to form stellar clumps at distances of several kiloparsecs from the cluster, so it is not a phenomenon confined to the inner part of Palomar 5's tails, as previously suggested. Our models can reproduce the density contrast between the clumps and the surrounding tails found in the observed streams, without including any lumpiness in the dark halo, suggesting new upper limits on its granularity.

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The Orbits of 48 Globular Clusters in a Milky Way–like Barred Galaxy

Cited by 78 publications

References 35 publications

Dissolution is the solution: on the reduced mass-to-light ratios of Galactic globular clusters

Dissolution is the solution: on the reduced mass-to-light ratios of Galactic globular clusters

Absolute proper motion of the Galactic open cluster M 67

Clumpy streams in a smooth dark halo: the case of Palomar 5

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