The ACS Fornax Cluster Survey. IX. The Color-Magnitude Relation of Globular Cluster Systems - Astrophysics > Cosmology and Nongalactic AstrophysicsReport as inadecuate




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Abstract: We investigate the color-magnitude relation for globular clusters GCs -the so-called -blue tilt- detected in the ACS Fornax Cluster Survey andusing the combined sample of GCs from the ACS Fornax and Virgo Cluster Surveys.We find a tilt of gamma z=dg-z-dz=-0.0257 +- 0.0050 for the full GC sample ofthe Fornax Cluster Survey ~5800 GCs. This is slightly shallower than thevalue gamma z=-0.0459 +- 0.0048 found for the Virgo Cluster Survey GC sample~11100 GCs. The slope for the merged Fornax and Virgo datasets ~16900 GCsis gamma z=-0.0293 +- 0.0085, corresponding to a mass-metallicity relation of Z~ M^0.43. We find that the blue tilt sets in at GC masses in excess of M ~2*10^5 M sun. The tilt is stronger for GCs belonging to high-mass galaxies M *> 5 * 10^10 M sun than for those in low-mass galaxies M * < 5 * 10^10 M sun.It is also more pronounced for GCs with smaller galactocentric distances. Ourfindings suggest a range of mass-metallicity relations Z GC ~ M GC^0.3-0.7which vary as a function of host galaxy mass-luminosity. We compare ourobservations to a recent model of star cluster self-enrichment with generallyfavorable results. We suggest that, within the context of this model, theproto-cluster clouds out of which the GCs formed may have had density profilesslightly steeper than isothermal and-or star formation efficiencies somewhatbelow 0.3. We caution, however, that the significantly different appearance ofthe CMDs defined by the GC systems associated with galaxies of similar mass andmorphological type pose a challenge to any single mechanism that seeks toexplain the blue tilt. We therefore suggest that the merger-accretion historiesof individual galaxies have played a non-negligible role determining thedistribution of GCs in the CMDs of individual GC systems.



Author: S. Mieske, A. Jordan, P. Cote, E. Peng, L. Ferrarese, J. Blakeslee, S. Mei, H. Baumgardt, J. Tonry, L. Infante, M. West

Source: https://arxiv.org/



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