The Next Generation Virgo Cluster Survey. XVII. A Search for Planetary Nebulae in Virgo Cluster Globular Clusters
Résumé
The occurrence of planetary nebulae (PNe) in globular clusters (GCs) provides an excellent chance to study low-mass stellar evolution in a special (low-metallicity, high stellar density) environment. We report a systematic spectroscopic survey for the [O III] 5007 Å emission line of PNe in 1469 Virgo GCs and 121 Virgo ultra-compact dwarfs (UCDs), mainly hosted in the giant elliptical galaxies M87, M49, M86, and M84. We detected zero PNe in our UCD sample and discovered one PN ({M}5007=-4.1 {mag}) associated with an M87 GC. We used the [O III] detection limit for each GC to estimate the luminosity-specific frequency of PNe, α, and measured α in the Virgo cluster GCs to be α ∼ {3.9}-0.7+5.2× {10}-8 {PN}/{L}⊙ . The value of α in the Virgo GCs is among the lowest reported in any environment, due in part to the large sample size, and it is 5-6 times lower than that for the Galactic GCs. We suggest that α decreases toward brighter and more massive clusters, sharing a similar trend as the binary fraction, and the discrepancy between the Virgo and Galactic GCs can be explained by the observational bias in extragalactic surveys toward brighter GCs. This low but nonzero efficiency in forming PNe may highlight the important role played by binary interactions in forming PNe in GCs. We argue that a future survey of less massive Virgo GCs will be able to determine whether PN production in the Virgo GCs is governed by an internal process (mass, density, binary fraction) or if it is largely regulated by the external environment.