The mass function of the Arches cluster from Gemini adaptive optics data
Abstract
We have analysed high resolution adaptive optics (AO) science demonstration data of the young, massive stellar cluster Arches near the Galactic Center, obtained with the Gemini North telescope in combination with the University of Hawai'i AO system Hokupa'a. The AO H and K' photometry is calibrated using HST/NICMOS observations in the equivalent filters F160W and F205W obtained by Figer et al. (\cite{FKM}). The calibration procedure allows a detailed comparison of the ground-based adaptive optics observations against diffraction limited space-based photometry. The spatial resolution as well as the overall signal-to-noise ratio of the Gemini/Hokupa'a data is comparable to the HST/NICMOS data. The low Strehl ratio of only a few percent is the dominant limiting factor in the Gemini AO science demonstration data as opposed to space-based observations. After a thorough technical comparison, the Gemini and HST data are used in combination to study the spatial distribution of stellar masses in the Arches cluster. Arches is one of the densest young clusters known in the Milky Way, with a central density of ~ 3 x 105 Msun pc-3 and a total mass of about 104 Msun. A strong colour gradient is observed over the cluster field. The visual extinction increases by Delta AV ~ 10 mag over a distance of 15\arcsec from the cluster core. Extinction maps reveal a low-extinction cavity in the densest parts of Arches (R <= 5arcsec ), indicating the depletion of dust due to stellar winds or photo-evaporation. We correct for the change in extinction over the field and show that the slope of the mass function is strongly influenced by the effects of differential extinction. We obtain present-day mass function slopes of Gamma ~ -0.8 +/- 0.2 in the mass range 6 < M < 65 Msun from both data sets. The spatial analysis reveals a steepening of the mass function slope from close to zero in the cluster center to Gamma ~ -1.7 +/- 0.7 at R > 10arcsec , in accordance with a Salpeter slope (Gamma = -1.35). The bias in the mass function towards high-mass stars in the Arches center is a strong indication for mass segregation. The dynamical and relaxation timescales for Arches are estimated, and possible mass segregation effects are discussed with respect to cluster formation models. Based on observations obtained with the Gemini North Telescope and the NASA/ESA Hubble Space Telescope.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 2002
- DOI:
- 10.1051/0004-6361:20021118
- arXiv:
- arXiv:astro-ph/0208321
- Bibcode:
- 2002A&A...394..459S
- Keywords:
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- open clusters and associations: individual: Arches;
- stars: luminosity function;
- mass function;
- stars: early-type;
- stars: formation;
- ISM: dust;
- extinction;
- instrumentation: adaptive optics;
- Astrophysics
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