Absolute $V$-band magnitudes and mass-to-light ratios of Galactic globular clusters. (2020)

• Record Type: Journal Article
• Authors: Baumgardt, H.; Sollima, A.; Hilker, M.
• Is Part Of: Publications of the Astronomical Society of Australia. Volume 37(2020)
• Publication Date: 2020
• Subjects: globular clusters: general, -- stars: luminosity function, -- mass function; Astronomy -- Periodicals; Southern sky (Astronomy) -- Periodicals; Astrophysics -- Periodicals; Periodicals; 520.5
• DOI: 10.1017/pasa.2020.38
• Languages: English
• ISSNs: 1323-3580

Abstract

Abstract: We have used Hubble Space Telescope and ground-based photometry to determine total V -band magnitudes and mass-to-light ratios of more than 150 Galactic globular clusters. We do this by summing up the magnitudes of their individual member stars, using colour-magnitude information, Gaia DR2 proper motions, and radial velocities to distinguish cluster stars from background stars. Our new magnitudes confirm literature estimates for bright clusters with $V<8$, but can deviate by up to two magnitudes from literature values for fainter clusters. They lead to absolute mass-to-light ratios that are confined to the narrow range $1.4<M/L_V<2.5$, significantly smaller than what was found before. We also find a correlation between a cluster's $M/L_V$ value and its age, in agreement with theoretical predictions. The $M/L_V$ ratios of globular clusters are also in good agreement with those predicted by stellar isochrones, arguing against a significant amount of dark matter inside globular clusters. We finally find that, in agreement with what has been seen in M 31, the magnitude distribution of outer halo globular clusters has a tail towards faint clusters that is absent in the inner parts of the Milky Way.