A 2dF spectroscopic study of globular clusters in NGC 5128: Probing the formation history of the nearest giant Elliptical - AstrophysicsReportar como inadecuado




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Abstract: We have performed a spectroscopic study of globular clusters GCs in thegiant elliptical NGC 5128 using the 2dF facility at the Anglo-Australiantelescope. We obtained integrated optical spectra for a total of 254 GCs, 79 ofwhich are newly confirmed on the basis of their radial velocities and spectra.In addition, we obtained an integrated spectrum of the galaxy starlight alongthe southern major axis. We derive an empirical metallicity distributionfunction MDF for 207 GCs ~14 of the estimated total GC system based uponMilky Way GCs. This MDF is multimodal at high statistical significance withpeaks at Z-H~-1.3 and -0.5. A comparison between the GC MDF and that of thestellar halo at 20 kpc ~4 Reff reveals close coincidence at the metal-richends of the distributions. However, an inner 8 kpc stellar MDF shows a clearexcess of metal-rich stars when compared to the GCs. We compare a higher S-Nsubsample 147 GCs with two stellar population models which include non-solarabundance ratio corrections. The vast majority of our sample ~90% appearsold, with ages similar to the Milky Way GC system. There is evidence for apopulation of intermediate-age ~4-8 Gy GCs <15% of the sample which are onaverage more metal-rich than the old GCs. We also identify at least one youngercluster ~1-2 Gy in the central regions of the galaxy. Our observations areconsistent with a picture where NGC 5128 has undergone at least two mergersand-or interactions involving star formation and limited GC formation sincez=1, however the effect of non-canonical hot stellar populations on theintegrated spectra of GCs remains an outstanding uncertainty in our GC ageestimates.



Autor: Michael Beasley, Terry Bridges, Eric Peng, William E. Harris, Gretchen L.H. Harris, Duncan A. Forbes, Glen Mackie

Fuente: https://arxiv.org/







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