Integrated colours of Milky Way globular clusters and horizontal branch morphology

Smith, Graeme H.; Strader, Jay

doi:10.1002/asna.200610711

Cited by 12 publications

(15 citation statements)

References 71 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the figure, it is apparent that GCs with unusually extended HBs show colours that are roughly consistent with those GCs with normal HBs. This is in agreement with Smith & Strader (2007) who found no residual HB trend with common optical colours (although they did not analysis B − R colours) after correlations with metallicity were removed.…”

Section: Resultssupporting

confidence: 91%

Extending the baseline:Spitzermid-infrared photometry of globular cluster systems in the Centaurus A and Sombrero Galaxies

Spitler

Forbes

Beasley

2008

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Spitzer IR Array Camera (IRAC) mid-infrared photometry is presented for the globular cluster (GC) systems of the NGC 5128 ('Centaurus A') and NGC 4594 ('Sombrero') galaxies. Existing optical photometric and spectroscopic are combined with this new data in a comprehensive optical-to-mid-IR colour catalogue of 260 GCs. Empirical colour-metallicity relationships are derived for all optical-to-mid-IR colour combinations.These colours prove to be very effective quantities to test the photometric predictions of simple stellar population (SSP) models. In general, four SSP models show larger discrepancies between each other and the data at bluer wavelengths, especially at high metallicities. Such differences become very important when attempting to use colour-colour model predictions to constrain the ages of stellar populations. Furthermore, the age-substructure determined from colour-colour diagrams and 91 NGC 5128 GCs with spectroscopic ages from Beasley et al. is inconsistent, suggesting any apparent GC system age-substructure implied by a colour-colour analysis must be verified independently.Unlike blue wavebands, certain optical-to-mid-IR colours are insensitive to the flux from hot horizontal branch stars and thus provide an excellent metallicity proxy. The NGC 5128 GC system shows strong bimodality in the optical R band to mid-IR colour distributions, hence proving it is bimodal in metallicity. In this new colour space, a colour-magnitude trend, a 'blue tilt', is found in the NGC 5128 metal-poor GC data. The NGC 5128 young GCs do not contribute to this trend. In the NGC 4594 GC system, a population of abnormally massive GCs at intermediate metallicities shows bluer optical-to-optical colours for their optical-tomid-IR colours, suggesting they contain extended horizontal branches and/or are younger than typical GCs. Analysis of optical-to-mid-IR colours for a ultracompact dwarf galaxy suggests its metallicity is just below solar.

show abstract

Section: Resultssupporting

confidence: 91%

Extending the baseline:Spitzermid-infrared photometry of globular cluster systems in the Centaurus A and Sombrero Galaxies

Spitler

Forbes

Beasley

2008

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…Figure 6c illustrates that if mass loss in the preferential mode would be ignored, uncertainties up to 0.2 mag (0.1 mag up and down) should be included for computed cluster colours at a any fixed age and metallicity. This happens to be the same colour spread at fixed metallicity as found by Smith & Strader (2007) in their colourmetallicity relation.…”

Section: Colours Of Globular Clusterssupporting

confidence: 82%

“…(7) The typical colour range of globular clusters is covered by our models. When considering the colour-metallicity relation as reported by Smith & Strader (2007), from an order-ofmagnitude comparison we suggest that the observed colour scatter at fixed metallicity could be the effect of the preferential loss of low-mass stars. (8) Only when adopting a Salpeter IMF down to m min,i = 0.1 M , the mass-to-light ratios of UCDs are reproduced by our models.…”

Section: Discussionmentioning

confidence: 58%

See 1 more Smart Citation

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

View full text Add to dashboard Cite

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.

show abstract

“…The nuclear cluster has a stellar mass typical of globular clusters (GCs) and a (V − I) 0 color compatible with the most metal-poor Galactic GCs (Smith & Strader 2007). It fits well the relation between r h and C of Galactic globular clusters (GGC, Djorgovski et al 2003), but its concentration parameter is lower than any GGC with similar M V (Djorgovski & Meylan 1994).…”

Section: The Stellar Nucleussupporting

confidence: 58%

The strange case of the peculiar spiral galaxy NGC 5474

Bellazzini¹,

Annibali²,

Tosi³

et al. 2020

A&A

View full text Add to dashboard Cite

We present the first analysis of the stellar content of the structures and substructures identified in the peculiar star-forming galaxy NGC 5474, based on Hubble Space Telescope resolved photometry from the LEGUS survey. NGC 5474 is a satellite of the giant spiral M 101, and is known to have a prominent bulge that is significantly off-set from the kinematic center of the underlying H i and stellar disc. The youngest stars (age≤ 100 Myr) trace a flocculent spiral pattern extending out to > ∼ 8 kpc from the center of the galaxy. On the other hand intermediate-age (age > ∼ 500 Myr) and old (age ≥ 2 Gyr) stars dominate the off-centred bulge and a large substructure residing in the South Western part of the disc and not correlated with the spiral arms (SW over-density). The old age of the stars in the SW over-density suggests that this may be another signature of the dynamical interaction/s that have shaped this anomalous galaxy. We suggest that a fly by with M 101, generally invoked as the origin of the anomalies, may not be sufficient to explain all the observations. A more local and more recent interaction may help to put all the pieces of this galactic puzzle together.

show abstract

Integrated colours of Milky Way globular clusters and horizontal branch morphology

Cited by 12 publications

References 71 publications

Extending the baseline:Spitzermid-infrared photometry of globular cluster systems in the Centaurus A and Sombrero Galaxies

Extending the baseline:Spitzermid-infrared photometry of globular cluster systems in the Centaurus A and Sombrero Galaxies

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

The strange case of the peculiar spiral galaxy NGC 5474

Contact Info

Product

Resources

About