A Two-Phase Chemical Enrichment Model for the Milky Way Globular Cluster System

VanDalfsen, M. L.; Harris, William E.

doi:10.1086/380227

Cited by 24 publications

(23 citation statements)

References 32 publications

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“…An alternative approach, although still simplistic at this point, would be to introduce pre-enrichment of the proto-GCs (VanDalfsen & Harris 2004;Forte et al 2007) and invoke higher pre-enrichment for higher-mass clusters. Different amounts of pre-enrichment among GCs, presumably drawn from their host giant molecular clouds, would in principle allow for a wider range of environmental influences.…”

Section: Mass-metallicity Trendsmentioning

confidence: 99%

Globular Cluster Systems in Brightest Cluster Galaxies. Iii. Beyond Bimodality

Harris

Ciccone

Eadie

et al. 2017

ApJ

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We present new deep photometry of the rich globular cluster (GC) systems around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143 (Abell 2147), obtained with the Hubble Space Telescope (HST) ACS and WFC3 cameras. For comparison, we also present new reductions of similar HST/ACS data for the Coma supergiants NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to the radial limits of our data, comprising from 12,000 to 23,000 clusters per galaxy). The metallicity distribution functions (MDFs) of the GCs can still be matched by a bimodal-Gaussian form where the metal-rich and metalpoor modes are separated by 0.8 dex, but the internal dispersions of each mode are so large that the total MDF becomes very broad and nearly continuous from [Fe/H];−2.4 to solar. There are, however, significant differences between galaxies in the relative numbers of metal-rich clusters, suggesting that they underwent significantly different histories of mergers with massive gas-rich halos. Last, the proportion of metal-poor GCs rises especially rapidly outside projected radii  R R 4 eff , suggesting the importance of accreted dwarf satellites in the outer halo. Comprehensive models for the formation of GCs as part of the hierarchical formation of their parent galaxies will be needed to trace the systematic change in structure of the MDF with galaxy mass, from the distinctly bimodal form in smaller galaxies up to the broad continuum that we see in the very largest systems.

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Section: Mass-metallicity Trendsmentioning

confidence: 99%

Globular Cluster Systems in Brightest Cluster Galaxies. Iii. Beyond Bimodality

Harris

Ciccone

Eadie

et al. 2017

ApJ

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“…Very similar models have also been used for the halo of the Milky Way ( Prantzos 2003), and the globular cluster systems of large galaxies (VanDalfsen & Harris 2004), among other situations. Briefly, in this first-order model we envisage an ''accreting box'' in which a region of initial gas mass M 0 turns itself into stars through a long succession of starforming episodes, during which more gas is continuously flowing into the region.…”

Section: Matching To Chemical Evolution Modelsmentioning

confidence: 99%

“…For an example of the accreting-box model applied to a still more distinct two-stage model, see VanDalfsen & Harris (2004) and their discussion of bimodal MDFs for globular cluster systems. Several possible combinations of parameters are shown there, along with a nonlinear statistical procedure for finding the best-fitting parameters for an assumed model.…”

Section: Matching To Chemical Evolution Modelsmentioning

confidence: 99%

The Leo Elliptical NGC 3379: A Metal‐Poor Halo Emerges

Harris¹,

Harris²,

Layden³

et al. 2007

ApJ

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120

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We have used the ACS camera on HST to obtain (V, I ) photometry for 5300 red giant stars in the halo of the dominant Leo group member NGC 3379, a galaxy usually regarded as a classic normal giant elliptical. We use this data to derive the metallicity distribution function ( MDF ) for its outer-halo field stars at a location centered 33 kpc from the galaxy center. In at least two ways the MDF is distinctly unlike all the other E galaxies for which similar data exist. First, the NGC 3379 MDF is extremely broad and flat, with many stars at every interval in [m / H ]. Second, we see a metallicity gradient such that in ithe outermost parts of the field the low-metallicity stars (½m/H < À0:7) begin to dominate and the higher metallicity stars are rapidly diminishing. We find that a distinct two-stage chemical evolution model is necessary to explain the MDF shape. Our target field is centered at a projected distance of 12R e , twice as far out in units of effective radius as in any of the other galaxies yet surveyed. If NGC 3379 is indeed representative of large E/S0 galaxies, we predict that other such galaxies will reveal diffuse low-metallicity subpopulations, but that photometry at radii r ' (10Y15)R e will be necessary to get beyond the edge of the dominant metal-rich component.

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“…6). This further complicates explaining the observed mass-to-light ratios, since globular cluster metallicities are typically Z = 0.0004−0.014 (VanDalfsen & Harris 2004). Dynamical effects are thus needed to explain the even smaller mass-to-light ratio of Galactic globular clusters.…”

Section: Application To Globular Clustersmentioning

confidence: 99%

The photometric evolution of star clusters and the preferential loss of low-mass bodies – with an application to globular clusters

Kruijssen

Lamers

2008

A&A

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Context. To obtain an accurate description of broad-band photometric star cluster evolution, certain effects should be accounted for. Energy equipartition leads to mass segregation and the preferential loss of low-mass stars, while stellar remnants severely influence cluster mass-to-light ratios. Moreover, the stellar initial mass function and cluster metallicity affect photometry as well. Due to the continuous production of stellar remnants, their impact on cluster photometry is strongest for old systems like globular clusters. This, in combination with their low metallicities, evidence for mass segregation, and a possibly deviating stellar initial mass function, makes globular clusters interesting test cases for cluster models. Aims. In this paper we describe cluster models that include the effects of the preferential loss of low-mass stars, stellar remnants, choice of initial mass function and metallicity. The photometric evolution of clusters is predicted, and the results are applied to Galactic globular clusters. Methods. The cluster models presented in this paper represent an analytical description of the evolution of the underlying stellar mass function due to stellar evolution and dynamical cluster dissolution. Stellar remnants are included by using initial-remnant mass relations, while cluster photometry is computed from the Padova 1999 isochrones. Results. Our study shows that the preferential loss of low-mass stars strongly affects cluster magnitude, colour and mass-to-light ratio evolution, as it increases cluster magnitudes and strongly decreases mass-to-light ratios. The effects of stellar remnants are prominent in the evolution of cluster mass, magnitude and mass-to-light ratio, while variations of the initial mass function induce similar, but smaller changes. Metallicity plays an important role for cluster magnitude, colour and mass-to-light ratio evolution. The different effects can be clearly separated with our models. We apply the models to the Galactic globular cluster population. Its properties like the magnitude, colour and mass-to-light ratio ranges are well reproduced with our models, provided that the preferential loss of lowmass stars and stellar remnants are included. We also show that the mass-to-light ratios of clusters with similar ages and metallicities cannot be assumed to be constant for all cluster luminosities due to the mass-dependence of the half-mass relaxation time. Instead, mass-to-light ratio increases with cluster luminosity and mass. Conclusions. These models underline the importance of more detailed cluster models when considering cluster photometry. By including the preferential loss of low-mass stars and the presence of stellar remnants, the magnitude, colour and mass-to-light ratio ranges of modelled globular clusters are significantly altered. With the analytic framework provided in this paper, observed cluster properties can be interpreted in a more complete perspective.

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A Two-Phase Chemical Enrichment Model for the Milky Way Globular Cluster System

Cited by 24 publications

References 32 publications

Globular Cluster Systems in Brightest Cluster Galaxies. Iii. Beyond Bimodality

Globular Cluster Systems in Brightest Cluster Galaxies. Iii. Beyond Bimodality

The Leo Elliptical NGC 3379: A Metal‐Poor Halo Emerges

The photometric evolution of star clusters and the preferential loss of low-mass bodies – with an application to globular clusters

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