A&A 366, 54-61 (2001)
DOI: 10.1051/0004-6361:20000080

Anomalous surface brightness fluctuations in NGC 4489

S. Mei^{1, 2}, D. R. Silva² and P. J. Quinn<sup>2

1</sup>  Observatoire Midi-Pyrénées, 14 Av. E. Belin, 31400 Toulouse, France
²  European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany

(Received 18 February 2000 / Accepted 30 October 2000)

Abstract
Anomalously high K-band surface brightness fluctuations (SBF) have been reported in NGC 4489 by Pahre & Mould (1994), Jensen et al. (1996) and Jensen et al. (1998). However, these conclusions were uncertain because of relatively low signal-to-noise data. New high signal-to-noise data for NGC 4489 have been obtained at the NOAO/KPNO 2.1 m and the ESO/La Silla 3.5 m NTT telescopes. Adopting the I-band SBF distance modulus determined by Tonry et al. (2000b) and the versus (V-I) calibration of Tonry et al. (2000a), a value of mag was derived. Relative to the average empirical derived for giant ellipticals by Jensen et al. (1998) ( mag), the detection of an anomalous K-band SBF in NGC 4489 is confirmed at the two sigma level. Such anomalous fluctuations could be caused by an extended giant branch, consisting of either intermediate-age AGB stars above the tip of the first-ascent giant branch or high-metallicity first-ascent giants, or by lack of a full understanding of the K-band SBF calibration. This result raises questions about the accuracy of K-band SBF distance measurements for elliptical galaxies with unknown stellar composition and underscores the need for measurements over a larger range of color and luminosity.

Key words: galaxies: distances and redshift -- individual: NGC 4489

Offprint request: S. Mei, mei@ast.obs-mip.fr

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© ESO 2001

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