Junge massereiche Sternhaufen in 3D - spektrophotometrisches Kartographieren mit MUSE
Zusammenfassung der Projektergebnisse
In this work, we performed a full spectroscopic analysis of the stellar and gas content of the young star cluster Westerlund 2, located in the Milky Way, using Hubble Space Telescope photometry, VLT/MUSE integral field spectroscopy, and data from the second Gaia data release (DR2). To reduce VLT/MUSE data in crowded regions like young star clusters that have a high and locally varying background caused by the parental H II region, we developed a new method to subtract Telluric lines from the Earth’s atmosphere without over subtracting the local gas emissions. To further analyze and characterize the radial velocity profile of the extracted stars in such young cluster we also developed a python module that allows us to accurately determine stellar radial velocities with an accuracy of ∼ 2 km s^-1 based on strong absorption lines without the need of stellar spectral template libraries. All of these tools are publish as the python package MUSEpack. The creation of a pixel-to-pixel high resolution radial velocity map of the gas and comparing it with the existing color-excess map showed that the H II region expands with a rate of ∼ 15 km s-1 , driven by the winds and far-ultraviolet fluxes of the many O and B stars in the cluster center. An extensive, Markov-Chain Monte Carlo (MCMC) supported analysis of the radial velocity distribution of the cluster member stars revealed: 1) stars of different masses show different velocity distribution, 2) the lower the stellar mass, the higher the velocity dispersion, and 3) the low mass, late-type pre-main sequence stars show five distinct velocity groups. The O and B stars group in one and two distinct radial velocity peaks and are mainly located in the center of Westerlund 2, as expected for a highly mass-segregated cluster. For the premain sequence population, stars of always two of the 5 distinct peaks are co-located with each of two clumps Westerlund 2 is built from and the fifth group shows a halo-like structure. These structures led us conclude that this is the imprint from the initial cloud-collapse responsible for the cluster’s formation. A thorough analysis of the dynamical state determined a dynamical mass range for the cluster of Mdyn,Wd2 = (7.5 ± 1.9) · 10^4 − (4.4 ± 1.1) · 10^5 M , which highly exceeds the photometric mass Mphot,Wd2 = 3.7 · 10^4 M and suggests that Westerlund 2 will dissolve in the future. While the Gaia DR2 data supports our results we were unable to use it as an independent confirmation. The crowding and the high extinctions in young star clusters still introduces too much uncertainties in the stellar proper motions. This analysis also identified 22 candidate runaway stars with peculiar velocities between 30 and 546 km s^-1 . The methods introduced and published through this project will allow similar studies in the future to compare these results to other young star clusters in the Milky Way and the Magellanic Clouds. It is also possible to transfer the code to be used with other instruments, especially the upcoming James Webb Space Telescope (JWST), which will allow observations using photometry and integral field spectroscopy in the near and mid infrared, with a sensitivity and at wavelengths where the youngest and lowest-mass stars and brown dwarfs can be observed throughout the Local Group.
Projektbezogene Publikationen (Auswahl)
- The Young Massive Star Cluster Westerlund 2 Observed with MUSE. II. MUSEpack – A Python Package to Analyze the Kinematics of Young Star Clusters, 2019 AJ, 158, 201
Zeidler P., Nota A., Sabbi E., Luljak P., McLeod A. F., Grebel E. K.; Pasquali A., Tosi M.
(Siehe online unter https://doi.org/10.3847/1538-3881/aae258) - Star Clusters Near and Far; Tracing Star Formation Across Cosmic Time, 2020 SSRv, 216, 69
Adamo A.; Zeidler P.; Kruijssen J. M. Diederik; Chevance M. Gieles M.; Calzetti D.; Charbonnel C.; Zinnecker H.; Krause M. G. H.
(Siehe online unter https://doi.org/10.1007/s11214-020-00690-x) - Stellar Feedback and Resolved Stellar IFU Spectroscopy in the Nearby Spiral Galaxy NGC 300, 2020 ApJ, 891, 25
McLeod A. F.; Kruijssen J. M. D.; Weisz, D. R.; Zeidler P.; Schruba A.; Dalcanton J. J.; Longmore S. N.; Chevance M.; Faesi C. M.; Byler N.
(Siehe online unter https://doi.org/10.3847/1538-4357/ab6d63)
