EDP Sciences
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Volume 366, Number 1, January IV 2001
Page(s) 54 - 61
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20000080

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

Anomalous surface brightness fluctuations in NGC 4489

S. Mei1, 2, D. R. Silva2 and P. J. Quinn2

1  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)

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 $\overline M_I$ versus (V-I) calibration of Tonry et al. (2000a), a value of $\overline M_K =-6.29\pm0.10 $ mag was derived. Relative to the average empirical $\overline M_K$ derived for giant ellipticals by Jensen et al. (1998) ( $\overline M_K=-5.61\pm0.12$ 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 $\overline M_K$ 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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