Hostname: page-component-8448b6f56d-42gr6 Total loading time: 0 Render date: 2024-04-23T17:31:03.463Z Has data issue: false hasContentIssue false
  • English
  • Français

Why Haven't Loose Globular Clusters Collapsed yet?

Published online by Cambridge University Press:  01 September 2007

Guido De Marchi ,
Francesco Paresce  and
Luigi Pulone
Guido De Marchi
Affiliation:
ESA, Space Science Department, 2200 AG Noordwijk, Netherlands email: gdemarchi@rssd.esa.int
Francesco Paresce
Affiliation:
INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, 40129 Bologna, Italy email: paresce@iasfbo.inaf.it
Luigi Pulone
Affiliation:
INAF, Observatory of Rome, 00040 Monte Porzio Catone, Italy email: pulone@mporzio.astro.it
Rights & Permissions [Opens in a new window]

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

We report on the discovery of a surprising observed correlation between the slope of the low-mass stellar global mass function (GMF) of globular clusters (GCs) and their central concentration parameter c = log(rt/rc), i.e. the logarithmic ratio of tidal and core radii. This result is based on the analysis of a sample of twenty Galactic GCs, with solid GMF measurements from deep HST or VLT data, representative of the entire population of Milky Way GCs. While all high-concentration clusters in the sample have a steep GMF, low-concentration clusters tend to have a flatter GMF implying that they have lost many stars via evaporation or tidal stripping. No GCs are found with a flat GMF and high central concentration. This finding appears counter-intuitive, since the same two-body relaxation mechanism that causes stars to evaporate and the cluster to eventually dissolve should also lead to higher central density and possibly core-collapse. Therefore, severely depleted GCs should be in a post core-collapse state, contrary to what is suggested by their low concentration. Several hypotheses can be put forth to explain the observed trend, none of which however seems completely satisfactory. It is likely that GCs with a flat GMF have a much denser and smaller core than suggested by their surface brightness profile and may well be undergoing collapse at present. It is, therefore, likely that the number of post core-collapse clusters in the Galaxy is much larger than thought so far.

Keywords

Stars: luminosity functionmass function – Galaxy: globular clusters: general
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 3 , Symposium S246: Dynamical Evolution of Dense Stellar Systems , September 2007 , pp. 161 - 165
Copyright
Copyright © International Astronomical Union 2008

References

Andreuzzi, G., De Marchi, G., Ferraro, F., Paresce, F., & Pulone, L. 2001, A&A, 372, 851Google Scholar
Baumgardt, H. 2008, these proceedingsGoogle Scholar
Da Costa, , 1982, AJ, 87, 990CrossRefGoogle Scholar
Davis, S. & Richer, H. 2008, these proceedingsGoogle Scholar
De Marchi, G., Leibundgut, B., Paresce, F., & Pulone, L. 1999, A&A 343, 9LGoogle Scholar
De Marchi, G. & Paresce, F. 1995, A&A, 304, 202Google Scholar
De Marchi, G., Paresce, F., Portegies Zwart, S. 2005, in ASSL 327, The initial mass function 50 years later, Eds. Corbelli, E., Palla, F., Zinnecker, H. (Dordrecht: Springer), 77CrossRefGoogle Scholar
De Marchi, G., Paresce, F., & Pulone, L. 2000, ApJ, 530, 342CrossRefGoogle Scholar
De Marchi, G., Paresce, F., & Pulone, L. 2007, ApJ, 656, L65CrossRefGoogle Scholar
De Marchi, G. & Pulone, L. 2007, A&A, 467, 107Google Scholar
De Marchi, G., Pulone, L., & Paresce, F. 2006, A&A, 449, 161Google Scholar
Djorgovski, S. & King, R. 1986, ApJ, 305, L61CrossRefGoogle Scholar
Djorgovski, S. & Meylan, G. 1993, in ASP Conf. Ser. 50, Structure and Dynamics of Globular Clusters, S. Djorgovski, G. Meylan (San Francisco: ASP), 325Google Scholar
Elson, R., Hut, P., & Ingaki, S. 1987, ARAA, 25, 565CrossRefGoogle Scholar
Fan, X., et al. 1996, AJ, 112, 628CrossRefGoogle Scholar
Gnedin, O. & Ostriker, J. 1997, ApJ, 474, 223CrossRefGoogle Scholar
Harris, W. 1996, AJ 112, 1487CrossRefGoogle Scholar
Hut, P. 1985, in IAU Symp. 113, Dynamics of star clusters, (Dordrecht: Reidel), 231CrossRefGoogle Scholar
Koch, A., Grebel., E., Odenkirchen, M., Martinez–Delgado, D., & Caldwell, J. 2004, AJ, 128, 2274CrossRefGoogle Scholar
Kroupa, P. 2008, these proceedingsGoogle Scholar
Murphy, B., Cohn, H., & Hut, P. 1990, MNRAS, 245, 335Google Scholar
Paresce, F. & De Marchi, G. 2000, ApJ, 534, 870CrossRefGoogle Scholar
Paresce, F., De Marchi, G., & Jedrzejewski, R. 1995, ApJ, 442, L57CrossRefGoogle Scholar
Richer, H., Fahlman, G., Buonanno, R., Fusi Pecci, F., Searle, L., & Thompson, I. 1991 381, 147Google Scholar
Sirianni, M., Nota, A., De Marchi, G., Leitherer, C., & Clampin, M. 2002, ApJ, 579, 275CrossRefGoogle Scholar
Sollima, A., Beccari, G., Ferraro, F., Fusi Pecci, F., & Sarajedini, A. 2007, MNRAS, 380, 781CrossRefGoogle Scholar
Spitzer, L. 1987, Dynamical Evolution of Globular Clusters, (Princeton: Princeton Univ. Press)Google Scholar
Stetson, P., McClure, R., & VandenBerg, D. 2004, PASP, 116, 1012CrossRefGoogle Scholar
Trenti, M. 2007, American Astronomical Society, DDA meeting #38, #2.01Google Scholar
Trenti, M. 2008, these proceedingsGoogle Scholar
Trager, S., Djorgovski, S., & King, I. 1995, AJ, 109, 218CrossRefGoogle Scholar
Vesperini, E. & Heggie, D. 1997, MNRAS, 289, 898CrossRefGoogle Scholar