THE COLOR-MAGNITUDE RELATION FOR METAL-POOR GLOBULAR CLUSTERS IN M87: CONFIRMATION FROM DEEP HST/ACS IMAGING

Journal Article · Sun Sep 20 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/703/1/42· OSTI ID:21372031

Peng, Eric W ^[1]; Jordan, Andres ^[2]; Blakeslee, John P; Cote, Patrick; Ferrarese, Laura ^[3]; Mieske, Steffen ^[4]; Harris, William E; Madrid, Juan P ^[5]

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1. Department of Astronomy, Peking University, Beijing 100871 (China)
2. Departamento de AstronomIa y AstrofIsica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile)
3. Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
4. European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile)
5. Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 (Canada)

Metal-poor globular clusters (GCs) are our local link to the earliest epochs of star formation and galaxy building. Studies of extragalactic GC systems using deep, high-quality imaging have revealed a small but significant slope to the color-magnitude relation for metal-poor GCs in a number of galaxies. We present a study of the M87 GC system using deep, archival HST/ACS imaging with the F606W and F814W filters, in which we find a significant color-magnitude relation for the metal-poor GCs. The slope of this relation in the I versus V-I color-magnitude diagram (gamma {sub I} = -0.024 +- 0.006) is perfectly consistent with expectations based on previously published results using data from the ACS Virgo Cluster Survey. The relation is driven by the most luminous GCs, those with M{sub I} {approx}< -10, and its significance is largest when fitting metal-poor GCs brighter than M{sub I} = -7.8, a luminosity which is {approx}1 mag fainter than our fitted Gaussian mean for the luminosity function (LF) of blue, metal-poor GCs ({approx}0.8 mag fainter than the mean for all GCs). These results indicate that there is a mass scale at which the correlation begins, and is consistent with a scenario where self-enrichment drives a mass-metallicity relationship. We show that previously measured half-light radii of M87 GCs from best-fit PSF-convolved King models are consistent with the more accurate measurements in this study, and we also explain how the color-magnitude relation for metal-poor GCs is real and cannot be an artifact of the photometry. We fit Gaussian and evolved Schechter functions to the luminosity distribution of GCs across all colors, as well as divided into blue and red subpopulations, finding that the blue GCs have a brighter mean luminosity and a narrower distribution than the red GCs. Finally, we present a catalog of astrometry and photometry for 2250 M87 GCs.

• OSTI ID: 21372031
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 703; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COLOR
ELEMENTS
EVOLUTION
GALACTIC EVOLUTION
GALAXIES
LUMINOSITY
METALS
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
PHOTOMETRY
PHYSICAL PROPERTIES
STAR CLUSTERS
STARS