Explaining the Mysterious Age Gap of Globular Clusters in the Large Magellanic Cloud

Bekki, Kenji; Couch, Warrick J.; Beasley, Michael A.; Forbes, Duncan A.; Chiba, Masashi; Costa, G. S. Da

doi:10.1086/423372

Cited by 80 publications

(115 citation statements)

References 35 publications

(42 reference statements)

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“…Probably they are caused by associations, which have not yet dissolved. High velocity cloud-cloud collisions are another trigger mechanism of cluster formation (Zhang et al 2001;Bekki et al 2004). These collisions are particularly effective during galaxy interactions and mergers.…”

Section: Age Distributionmentioning

confidence: 99%

Ages and luminosities of young SMC/LMC star clusters and the recent star formation history of the Clouds

Glatt

Grebel

Koch

2010

A&A

166

213

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Aims. In this paper we discuss the age and spatial distribution of young (age < 1 Gyr) Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC) clusters using data from the Magellanic Cloud Photometric Surveys. Luminosities are calculated for all age-dated clusters. Methods. The ages of 324 and 1193 populous star clusters in the SMC and the LMC were determined fitting Padova and Geneva isochrone models to their resolved color-magnitude diagrams. The clusters cover an age range between 10 Myr and 1 Gyr in each galaxy. For the SMC, a constant distance modulus of (m − M) 0 = 18.90 and a metallicity of Z = 0.004 were adopted. For the LMC, we used a constant distance modulus of (m − M) 0 = 18.50 and a metallicity of Z = 0.008. For both galaxies, we used a variable color excess to derive the cluster ages. Results. We find two periods of enhanced cluster formation in both galaxies at 160 Myr and 630 Myr (SMC) and at 125 Myr and 800 Myr (LMC). We present the spatially resolved recent star formation history of both Clouds based on young star clusters. The first peak may have been triggered by a close encounter between the SMC and the LMC. In both galaxies, the youngest clusters reside in the supergiant shells, giant shells, the intershell regions, and toward regions with a high Hα content, suggesting that their formation is related to expansion and shell-shell interaction. Most of the clusters are older than the dynamical age of the supergiant shells. No evidence of cluster dissolution was found. Computed V band luminosities show a trend toward fainter magnitudes with increasing age, as well as a trend toward brighter magnitudes with increasing apparent cluster radii.

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Section: Age Distributionmentioning

confidence: 99%

Ages and luminosities of young SMC/LMC star clusters and the recent star formation history of the Clouds

Glatt

Grebel

Koch

2010

A&A

166

213

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“…High PNe abundances, that do not include iron, are confined to the bar and south eastern region of the LMC, indicating places were star formation was recently active (Leisy & Dennefeld 2006). According to Bekki et al (2004), the LMC experienced a close encounter with the SMC ∼4 Gyr ago. This event caused a new episode of star formation in both the field and cluster population as well as the formation of the LMC bar and Magellanic Stream.…”

Section: Chemical Enrichment and Dynamicsmentioning

confidence: 99%

“…At that time, the SMC had a close encounter with the LMC (Piatti et al 2005, Bekki et al 2004. Was this episode responsible for the formation of the Magellanic Bridge?…”

Section: Dynamics and The Magellanic Bridgementioning

confidence: 99%

The metallicity gradient as a tracer of history and structure: the Magellanic Clouds and M33 galaxies

Cioni¹

2009

A&A

133

154

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Context. The stellar metallicity and its gradient place constraints on the formation and evolution of galaxies. Aims. This is a study of the metallicity gradient of the LMC, SMC and M33 galaxies derived from their asymptotic giant branch (AGB) stars. Methods. The [Fe/H] abundance was derived from the ratio between C-and M-type AGB stars and its variation analysed as a function of galactocentric distance. Galaxy structure parameters were adopted from the literature.Results. The metallicity of the LMC decreases linearly as −0.047± 0.003 dex kpc −1 out to ∼8 kpc from the centre. In the SMC, [Fe/H] has a constant value of ∼−1.25 ± 0.01 dex up to ∼12 kpc. The gradient of the M33 disc, until ∼9 kpc, is −0.078 ± 0.003 dex kpc −1 while the outer disc/halo, out to ∼25 kpc, has [Fe/H] ∼ −1.7 dex. Conclusions. The metallicity of the LMC, as traced by different populations, bears the signature of two major star forming episodes: the first one constituting a thick disc/halo population and the second one a thin disc and bar due to a close encounter with the Milky Way and SMC. The [Fe/H] of the recent episode supports an LMC origin for the Stream. The metallicity of the SMC supports star formation, ∼3 Gyr ago, as triggered by LMC interaction and sustained by the bar in the outer region of the galaxy. The SMC [Fe/H] agrees with the present-day abundance in the Bridge and shows no significant gradient. The metallicity of M33 supports an "insideout" disc formation via accretion of metal poor gas from the interstellar medium.

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“…However, current ΛCDM models suggest that the majority of the MW´s building blocks were assimilated very early in its history and that existing low-mass galaxies like the SMC are survivors of this process and thus underwent a different chemical evolution (e.g., Robertson et al 2005). At the very least, many dynamical simulations (e.g., Bekki et al 2004) suggest that the MW, Large Magellanic Cloud (LMC), and SMC compose a longterm interacting system, with the SMC and LMC likely to be eventually consumed by the MW. In addition, close encounters in the last few Gyr may well have stimulated star formation on a global scale in both the SMC and LMC (Murai & Fujimoto 1980;Gardiner et al 1994;Yoshizawa & Noguchi 2003;Bekki et al 2004).…”

Section: Introductionmentioning

confidence: 99%

“…At the very least, many dynamical simulations (e.g., Bekki et al 2004) suggest that the MW, Large Magellanic Cloud (LMC), and SMC compose a longterm interacting system, with the SMC and LMC likely to be eventually consumed by the MW. In addition, close encounters in the last few Gyr may well have stimulated star formation on a global scale in both the SMC and LMC (Murai & Fujimoto 1980;Gardiner et al 1994;Yoshizawa & Noguchi 2003;Bekki et al 2004). These early simulations predict bursts of star formation ∼0.2 Gyr ago that led to the formation of the eastern wing of the SMC and the Magellanic Bridge, and a similar close encounter event some 4 Gyr ago.…”

Section: Introductionmentioning

confidence: 99%

Ca II TRIPLET SPECTROSCOPY OF SMALL MAGELLANIC CLOUD RED GIANTS. I. ABUNDANCES AND VELOCITIES FOR A SAMPLE OF CLUSTERS

Parisi

Grocholski

Geisler

et al. 2009

The Astronomical Journal

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We have obtained near-infrared spectra covering the Ca II triplet lines for a large number of stars associated with 16 Small Magellanic Cloud (SMC) clusters using the VLT + FORS2. These data compose the largest available sample of SMC clusters with spectroscopically derived abundances and velocities. Our clusters span a wide range of ages and provide good areal coverage of the galaxy. Cluster members are selected using a combination of their positions relative to the cluster center as well as their location in the color-magnitude diagram, abundances, and radial velocities (RVs). We determine mean cluster velocities to typically 2.7 km s −1 and metallicities to 0.05 dex (random errors), from an average of 6.4 members per cluster. By combining our clusters with previously published results, we compile a sample of 25 clusters on a homogeneous metallicity scale and with relatively small metallicity errors, and thereby investigate the metallicity distribution, metallicity gradient, and age-metallicity relation (AMR) of the SMC cluster system. For all 25 clusters in our expanded sample, the mean metallicity [Fe/H] = −0.96 with σ = 0.19. The metallicity distribution may possibly be bimodal, with peaks at ∼−0.9 dex and −1.15 dex. Similar to the Large Magellanic Cloud (LMC), the SMC cluster system gives no indication of a radial metallicity gradient. However, intermediate age SMC clusters are both significantly more metal-poor and have a larger metallicity spread than their LMC counterparts. Our AMR shows evidence for three phases: a very early (> 11 Gyr) phase in which the metallicity reached ∼−1.2 dex, a long intermediate phase from ∼10 to 3 Gyr in which the metallicity only slightly increased, and a final phase from 3 to 1 Gyr ago in which the rate of enrichment was substantially faster. We find good overall agreement with the model of Pagel & Tautvaišiene, which assumes a burst of star formation at 4 Gyr. Finally, we find that the mean RV of the cluster system is 148 km s −1 , with a velocity dispersion of 23.6 km s −1 and no obvious signs of rotation amongst the clusters. Our result is similar to what has been found from a wide variety of kinematic tracers in the SMC, and shows that the SMC is best represented as a pressure supported system.

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Explaining the Mysterious Age Gap of Globular Clusters in the Large Magellanic Cloud

Cited by 80 publications

References 35 publications

Ages and luminosities of young SMC/LMC star clusters and the recent star formation history of the Clouds

Ages and luminosities of young SMC/LMC star clusters and the recent star formation history of the Clouds

The metallicity gradient as a tracer of history and structure: the Magellanic Clouds and M33 galaxies

Ca II TRIPLET SPECTROSCOPY OF SMALL MAGELLANIC CLOUD RED GIANTS. I. ABUNDANCES AND VELOCITIES FOR A SAMPLE OF CLUSTERS

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