HSTcolour-magnitude diagrams of six old globular clusters in the LMC

Olsen, Knut; Hodge, P. W.; Mateo, M.; Olszewski, E; Schommer, R. A.; Suntzeff, N. B.; Walker, A. R.

doi:10.1046/j.1365-8711.1998.t01-1-01860.x

Cited by 8 publications

(10 citation statements)

References 29 publications

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“…It seems that there was a common epoch of the earliest star formation in at least some dwarf galaxies. Main-sequence photometry shows that the oldest globular clusters in the LMC, Sagittarius, and Fornax are as old as the oldest Galactic halo clusters (Olsen et al 1998, Montegriffo et al 1998. The same has been suggested for the oldest globulars in M 31 and M 33 , while the SMC began to form globular clusters ≈ 3 Gyr later (Mighell et al 1998).…”

Section: Old Populations -Ubiquitous?mentioning

confidence: 98%

Evolutionary Histories of Dwarf Galaxies in the Local Group

Grebel

1999

Symp. - Int. Astron. Union

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The star formation histories of Local Group (LG) dwarf galaxies and more distant potential LG members are reviewed. Problems in defining the spatial extent of the LG and membership are briefly discussed. The morphological types found in the LG are presented, and it is suggested that we see continuous evolution from low-mass dwarf irregulars (dIrrs) to dwarf spheroidal galaxies (dSph) in the LG.Star formation histories for LG dwarfs and nearby LG candidates are compiled using population boxes. No two dwarfs, irrespective of morphological type, show the same evolutionary history, and all vary widely in ages of their subpopulations and in their enrichment history. The lack of gas in dSphs and certain dwarf ellipticals (dEs) is puzzling both with respect to their star formation histories and the expected mass loss from red giants, but a new photoionization scenario may reconcile these contradictions. Old populations, often spatially very extended, may be a common property of dwarf galaxies, though their fractions can be very small. Almost all types of dwarf galaxies studied in detail so far show spatial variations in ages and abundances such as radial age/metallicity gradients. The observed star formation histories impose constraints on merger and accretion scenarios.Properties of the Milky Way dwarf spheroidals are compared to the M 31 dSphs and discussed in the framework of the ram pressure/tidal stripping scenario. It is demonstrated that the newly discovered LG dwarfs follow the same relationship for central surface brightness, mean metallicity, and absolute magnitude as the other LG dwarfs.

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Section: Old Populations -Ubiquitous?mentioning

confidence: 98%

Evolutionary Histories of Dwarf Galaxies in the Local Group

Grebel

1999

Symp. - Int. Astron. Union

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“…Therefore, we adopted the ages in the literature that we felt were on solid ground. In the LMC these clusters included NGC 1711, 1754, 1786, 1806, 1835, 1850, 1856, 1898, 1953, 2004, SL 503, and SL 569 (Hodge & Lee 1984Geisler et al 1997;Olsen et al 1998 A comparison of our photometrically determined ages with the ages from CMDs is given in Figure 3. We have plotted the clusters to show multiple ages determined from colors measured from different fields and to show the range in ages given from CMDs.…”

Section: Cluster Agesmentioning

confidence: 99%

“…Points with a connecting line are ages for the same cluster: from measurements of the cluster colors that appear in different fields (x-axis) or from a range in ages given from the CMDs (y-axis). The CMD ages are taken from Hodge & Lee (1984), Geisler et al (1997), Olsen et al (1998), Carney et al (1985), Mighell, Sarajedini, & French (1998a, 1998b. The clusters are identified in the text.…”

Section: Mass and Age Distributions In The Lmcmentioning

confidence: 99%

Cluster Mass Functions in the Large and Small Magellanic Clouds: Fading and Size-of-Sample Effects

Elmegreen²,

et al. 2003

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The properties of $939 star clusters in the Large and Small Magellanic Clouds were determined from ground-based CCD images in UBVR passbands. The areal coverage was extensive, corresponding to 11.0 kpc 2 in the LMC and 8.3 kpc 2 in the SMC. After corrections for reddening, the colors and magnitudes of the clusters were converted to ages and masses, and the resulting mass distributions were searched for the effects of fading, evaporation, and size-of-sample bias. The data show a clear signature of cluster fading below the detection threshold. The initial cluster mass function (ICMF) was determined by fitting the mass and age distributions with cluster population models. These models suggest a new method to determine the ICMF that is nearly independent of fading or disruption and is based on the slope of a correlation between age and the maximum cluster mass in equally spaced intervals of log age. For a nearly uniform star formation rate, this correlation has a slope equal to 1/( À 1) for an ICMF of dn(M)/dM / M À . We determine that is between 2 and 2.4 for the LMC and SMC using this method plus another method in which models are fitted to the mass distribution integrated over age and to the age distribution integrated over mass. The maximum mass method also suggests that the cluster formation rate in the LMC age gap between 3 and 13 Gyr is about a factor of 10 below that in the period from 0.1 to 1 Gyr. The oldest clusters correspond in age and mass to halo globular clusters in the Milky Way. They do not fit the trends for lower mass clusters but appear to be a separate population that either had a very high star formation rate and became depleted by evaporation or formed with only high masses.

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“…These works have produced a number of interesting results. (1) The oldest clusters of the LMC are coeval with GGCs Brocato et al 1996;Olsen et al 1998;Mackey & Gilmore 2004). The recent census of the old LMC globular clusters presented by Mackey & Gilmore (2004) counts a total of 15 objects with ages !10 Gyr.…”

Section: Introductionmentioning

confidence: 99%

The Globular Cluster NGC 1978 in the Large Magellanic Cloud

et al. 2007

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We have used deep, high-resolution Hubble Space Telescope ACS observations to image the cluster NGC 1978 in the Large Magellanic Cloud. This high-quality photometric data set allowed us to confirm the high ellipticity ( $ 0:30 AE 0:02) of this stellar system. The derived color-magnitude diagram allowed a detailed study of the main evolutionary sequences; in particular, we have detected the so-called bump along the red giant branch (at V 555 ¼ 19:10 AE 0:10). This is the first detection of this feature in an intermediate-age cluster. Moreover, the morphology of the evolutionary sequence and the population ratios have been compared with the expectations of different theoretical models (namely, BaSTI, Pisa Evolutionary Library [PEL], and Padua) in order to quantify the effect of convective overshooting. The best agreement (in terms of both morphology and star counts) has been found within the PEL isochrone, with Z ¼ 0:008 (consistent with the most recent determination of the cluster metallicity, ½M/H ¼ À0:37 dex) and a mild overshooting efficiency (Ã os ¼ 0:1). By adopting this theoretical set an age of ¼ 1:9 AE 0:1 Gyr has been obtained.

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HSTcolour-magnitude diagrams of six old globular clusters in the LMC

Cited by 8 publications

References 29 publications

Evolutionary Histories of Dwarf Galaxies in the Local Group

Evolutionary Histories of Dwarf Galaxies in the Local Group

Cluster Mass Functions in the Large and Small Magellanic Clouds: Fading and Size-of-Sample Effects

The Globular Cluster NGC 1978 in the Large Magellanic Cloud

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