The Flattening of Globular Clusters

Bergh, Sidney van den

doi:10.1088/0004-6256/135/5/1731

Cited by 31 publications

(17 citation statements)

References 25 publications

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“…Our M33 sample does not show any clear correlation with age or mass. A luminosity–ellipticity relation has also been suggested in some nearby galaxies (van den Bergh ). While the faintest clusters associated with massive galaxies (MW, M31 and NGC 5128) are flatter than the most luminous SCs, no evidence for a luminosity–ellipticity correlation exists in the LMC or SMC.…”

Section: Ellipticitiesmentioning

confidence: 69%

“…shows the mean ellipticity of different SC systems as a function of the luminosity of their host galaxy. The mean ellipticities were obtained from Harris () for the MW, Barmby et al (, ) for M31, van den Bergh () for the LMC and Hill & Zaritsky () for the SMC. The mean ellipticity for clusters in M33 corresponds to the mean value from Table from F 606 W band.…”

Section: Ellipticitiesmentioning

confidence: 99%

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Newly identified star clusters in M33 - III. Structural parameters

Roman

Sarajedini

Holtzman

et al. 2012

Monthly Notices of the Royal Astronomical Society

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We present the morphological properties of 161 star clusters in M33 using the Advanced Camera for Surveys Wide Field Channel on‐board the Hubble Space Telescope using observations with the F606W and F814W filters. We obtain, for the first time, ellipticities, position angles and surface brightness profiles for a significant number of clusters. On average, M33 clusters are more flattened than those of the Milky Way (MW) and M31, and more similar to clusters in the Small Magellanic Cloud (SMC). The ellipticities do not show any correlation with age or mass, suggesting that rotation is not the main cause of elongation in the M33 clusters. The position angles of the clusters show a bimodality with a strong peak perpendicular to the position angle of the galaxy major axis. These results support the notion that tidal forces are the reason for the cluster flattening. We fit King and Elson–Freeman–Fall (EFF) models to the surface brightness profiles and derive structural parameters including core radii, concentration, half‐light radii and central surface brightness for both filters. The surface brightness profiles of a significant number of clusters show irregularities such as bumps and dips. Young clusters (log age < 8) are notably better fitted by models with no radial truncation (EFF models), while older clusters show no significant differences between King and EFF fits. M33 star clusters seem to have smaller sizes, smaller concentrations and smaller central surface brightness as compared to clusters in the MW, M31, Large Magellanic Cloud and SMC. Analysis of the structural parameters presents an age–radius relation also detected in other star cluster systems. The overall analysis shows differences in the structural evolution between the M33 cluster system and cluster systems in nearby galaxies. These differences could have been caused by the strong differences in these various environments.

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Section: Ellipticitiesmentioning

confidence: 69%

Section: Ellipticitiesmentioning

confidence: 99%

Newly identified star clusters in M33 - III. Structural parameters

Roman

Sarajedini

Holtzman

et al. 2012

Monthly Notices of the Royal Astronomical Society

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“…Brighter and more massive clusters tend to be more compact, and brighter clusters tend to be also more elliptical. van den Bergh (2008) noticed that, while in the LMC there is no evidence for a correlation between ellipticity and luminosity, the four brightest SMC clusters are all very flattened having < ǫ >= 0.26. Interestingly, also ωCen, the brightest globular cluster of the MW, is one of its most elongated ones.…”

Section: Resultsmentioning

confidence: 99%

THE CLUSTER POPULATION OF THE IRREGULAR GALAXY NGC 4449 AS SEEN BY THEHUBBLEADVANCED CAMERA FOR SURVEYS

Annibali

Tosi

Aloisi

et al. 2011

The Astronomical Journal

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We present a study of the star cluster population in the starburst irregular galaxy NGC 4449 based on B, V, I, and Hα images taken with the Advanced Camera for Surveys on the Hubble Space Telescope. We derive the cluster properties such as size, ellipticity, and total magnitudes. Cluster ages and masses are derived fitting the observed spectral energy distributions with different population synthesis models. Our analysis is strongly affected by the age-metallicity degeneracy; however, if we assume a metallicity of ∼1/4 solar, as derived from spectroscopy of HII regions, we find that the clusters have ages distributed quite continuously over a Hubble time, and they have masses from ∼ 10 3 M ⊙ up to ∼ 2 × 10 6 M ⊙ , assuming a Salpeters' IMF down to 0.1 M ⊙ . Young clusters are preferentially located in regions of young star formation, while old clusters are distributed over the whole NGC 4449 field of view, like the old stars (although we notice that some old clusters follow linear structures, possibly a reflection of past satellite accretion). The high SF activity in NGC 4449 is confirmed by its specific frequency of young massive clusters, higher than the average value found in nearby spirals and in the LMC (but lower than in other starburst dwarfs such as NGC 1705 and NGC 1569), and by the flat slope of the cluster luminosity function (dN(L V ) ∝ L −1.5 V dL for clusters younger than 1 Gyr). We use the upper envelope of the cluster log(mass) versus log(age) distribution to quantify cluster disruption, and do not find evidence for the high (90%) long-term infant mortality found by some studies. For the red clusters, we find correlations between size, ellipticity, luminosity and mass: brighter and more massive clusters tend to be more compact, and brighter clusters tend to be also more elliptical.Subject headings: galaxies: dwarf -galaxies: individual (NGC 4449) -galaxies: -3 -irregular -galaxies: star clusters: general -galaxies: starburst -4 - IntroductionStar clusters are present in all types of galaxies, from the earliest to the latest morphological types, from the quietest to the most turbulent ones, such as merging and starburst systems. They are suggested to be the birth site of many (possibly most) stars, and provide an excellent tool to study the parent galaxy evolution through a long range of epochs. For these reasons, the interest in star cluster studies never fades. While Galactic star clusters were already studied a century ago, extragalactic ones have required the Data acquisition and reduction are summarized in Section 2, while the cluster analysis and the artificial cluster experiments are described in Section 3. The results (luminosity functions, ages and masses, cluster classification, correlations between cluster properties) are presented in Section 4. In Section 5 we investigate cluster disruption. The final results and discussion are presented in Section 6. Observations and data reductionHere we briefly recall the adopted observing strategy and main steps involved in the data reduct...

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“…Prior to the analysis, we corrected the LOS velocities for the effect of perspective rotation, using the systemic proper motions of the clusters listed in Table 1 and the method outlined in van de Ven et al (2006). The corrections we applied to the individual velocities reached from −0.15 km s −1 to 0.27 km s −1 for NGC 6791 and from −0.20 km s −1 to 0.19 km s −1 for NGC 6819.…”

Section: Line Of Sight Velocitiesmentioning

confidence: 99%

“…5, dashed green lines indicate the expected expansion or contraction of each cluster given its systemic velocity. The predictions were obtained by expressing the first two lines of equation 6 in van de Ven et al (2006) in polar coordinates. The mean values of the radial component in NGC 6791 are in reasonable agreement with the prediction.…”

Section: Gaia Proper Motionsmentioning

confidence: 99%

Linking the rotation of a cluster to the spins of its stars: the kinematics of NGC 6791 and NGC 6819 in 3D

Kamann

Bastian

Gieles

et al. 2018

Monthly Notices of the Royal Astronomical Society

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The physics governing the formation of star clusters is still not entirely understood. One open question concerns the amount of angular momentum that newly formed clusters possess after emerging from their parent gas clouds. Recent results suggest an alignment of stellar spins and binary orbital spins in star clusters, which support a scenario in which clusters are born with net angular momentum cascading down to stellar scales. In this paper, we combine Gaia data and published line of sight velocities to explore if NGC 6791 and NGC 6819, two of the clusters for which an alignment of stellar spins has been reported, rotate in the same plane as their stars. We find evidence for rotation in NGC 6791 using both proper motions and line of sight velocities. Our estimate of the inclination angle is broadly consistent with the mean inclination that has been determined for its stars, but the uncertainties are still substantial. Our results identify NGC 6791 as a promising follow-up candidate to investigate the link between cluster and stellar rotation. We find no evidence for rotation in NGC 6819.

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The Flattening of Globular Clusters

Cited by 31 publications

References 25 publications

Newly identified star clusters in M33 - III. Structural parameters

Newly identified star clusters in M33 - III. Structural parameters

THE CLUSTER POPULATION OF THE IRREGULAR GALAXY NGC 4449 AS SEEN BY THEHUBBLEADVANCED CAMERA FOR SURVEYS

Linking the rotation of a cluster to the spins of its stars: the kinematics of NGC 6791 and NGC 6819 in 3D

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