J/AJ/105/1762 Globular clusters around NGC 1399 (Ostrov+ 1993)
The metallicity gradient and distribution function of globular clusters around
NGC 1399
OSTROV P., GEISLER D., FORTE J.C.
<Astron. J. 105, 1762 (1993)>
=1993AJ....105.1762O 1993AJ....105.1762O
ADC_Keywords: Galaxies, optical; Clusters, globular; Photometry, CMT1T2V
Abstract:
We have obtained integrated Washington photometry (C,M,T1) of globular
cluster candidates in the field of NGC 1399. This galaxy, the dominant
object in the Fornax cluster, shares with NGC 4486 (M87) the property
of possessing one of the largest known specific frequencies of
globulars. Conflicting evidence on the presence of a B-V color gradient
as a function of galactocentric distance has been reported for this
cluster system. Here we investigate the existence of a gradient using
the C-T1 index, which is twice as metallicity sensitive as B-V. A small
gradient is detected. This color gradient, in the sense that outer
clusters are bluer, amounts to approx. 0.1 mag in C-T1 over a
galactocentric range from about 0.5 to 3.5 arcmin, corresponding to a
difference of approx. 0.2 dex in metallicity. This confirms
qualitatively the B-V gradient suggested by Bridges et al. [AJ, 101,
469 (1991)]. Photometry for 420 globular cluster candidates is
presented. Metal abundances internally precise to approx. 0.25 dex and
accurate to approx. 0.3 dex have been obtained for some 250 of the best
candidates, after statistically subtracting a field contamination
estimated at 30%. The mean abundance of -0.9 ± 0.2 confirms previous
indications that the NGC 1399 globular cluster system is, on average,
significantly more metal rich than that of the Galaxy, as expected from
the relative parent galaxy luminosities. Approximately 10% of the
clusters exceed solar abundance, similar to the case for NGC 5128. The
signature of possible globular cluster formation in mergers, as
suggested by Ashman and Zepf [ApJ, 384, 50 (1992)], is found in the
distinct peaks in the metallicity distribution function. However,
their prediction (based on a simple theory designed only for
application to normal elliptical galaxies and not the more complicated
cD galaxies represented by NGC 1399) that the color difference between
the clusters and the background halo light monotonically increases with
radius is not borne out by the observations. The difference decreases
with radius from the center to approx. 2 arcmin; beyond this radius,
the difference does appear to increase, however. At all radii, the mean
globular cluster abundance is some 0.25-0.5 dex more metal poor than
that of the background halo.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3 64 420 Washington Photometry of globular cluster
candidates in NGC 1399
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Byte-by-byte Description of file: table3
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Bytes Format Units Label Explanations
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1 I1 --- n_ID [0/3]? Field identification
Central field = 0, north field = 1
south field = 2 and west field = 3
2- 5 I4 --- ID Running ID number
6- 13 F8.2 pix X X coordinate
14- 21 F8.2 pix Y Y coordinate
22- 28 F7.3 mag C-M C-M color
29- 35 F7.3 mag M-T1 M-T1 color
36- 43 F8.3 mag T1 T1 magnitude
44- 50 F7.3 mag e_C-M Error in C-M
51- 57 F7.3 mag e_M-T1 Error in M-T1
58- 64 F7.3 mag e_T1 Error in T1
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Origin: AAS CD-ROM series, Volume 1, 1993
(End) Patricia Bauer [CDS] 06-Jul-1994