Astronomy & Astrophysics

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Issue		A&A Volume 369, Number 3, April III 2001
Page(s)		812 - 825
Section		Extragalactic astronomy
DOI		10.1051/0004-6361:20010180

A&A 369, 812-825 (2001)
DOI: 10.1051/0004-6361:20010180

Deep VLT search for globular clusters in NGC 5128: Color-magnitude diagrams and globular cluster luminosity function

M. Rejkuba^{1, 2}

¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
² Department of Astronomy, P. Universidad Católica, Casilla 306, Santiago 22, Chile

(Received 8 November 2000 / Accepted 31 January 2001 )

Abstract
At the distance of NGC 5128 ( $3.6\pm 0.2$ Mpc) it is possible to resolve globular clusters with high resolution imaging from the ground, thus allowing the globular cluster candidate selection primarily through their morphological properties. I report the discovery of 71 globular clusters in NGC 5128 on VLT UT1+FORS1 images, including the faintest members ( $M_V\sim-5$ ) known to date in this galaxy as well as in 5 previously-known clusters. U- and V-band photometry has been measured for all the candidates and the luminosity function, spanning -10.1< M_V< -4.9 and -9.3< M_U< -3.3, constructed. These are the deepest globular cluster luminosity functions in an elliptical galaxy determined so far. The Kolmogorov-Smirnov statistics show that the difference between the globular cluster luminosity functions of NGC 5128 and the MW is not larger than the difference between the ones of M 31 and the MW. The (U-V)₀ color histogram shows a bimodal distribution. For 23 globular clusters I obtained K-band images with SOFI at the NTT in La Silla. Their positions in the (U-V) vs. (V-K) color-color diagram indicate that they are indeed old globular clusters. Assuming that the globular clusters in NGC 5128 span a similar age range as the ones in the Milky Way and adopting a linear fit between the metallicity and (U-V)₀ color, the metal-rich clusters peak at ${\rm [Fe/H]}=-0.6$ dex and the metal-poor ones peak at ${\rm [Fe/H]}=-1.7$ dex.

Key words: galaxies: star clusters -- galaxies: formation -- galaxies: individual: NGC 5128

Offprint request: M. Rejkuba, mrejkuba@eso.org

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