J/ApJ/483/745 NGC 4478 globular clusters (Neilsen+ 1997)
The surface brightness fluctuations and globular cluster population of NGC 4478.
Neilsen E.H., Tsvetanov Z.I., Ford H.C.
<Astrophys. J. 483, 745 (1997)>
=1997ApJ...483..745N 1997ApJ...483..745N (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Photometry
Keywords: galaxies: distances - galaxies: individual (NGC 4478) -
galaxies: star clusters
Abstract:
We calculate the distance to NGC 4478, a neighbor of the giant Virgo
elliptical M87, using the surface brightness fluctuations method on
parallel data from the HST WFPC2 camera. The exposures considered were
taken through the F814W filter, which approximates the Johnson I, and
through the F606W filter, which is effectively a broad V filter. We
describe the use of Fourier methods for separation of the fluctuations
due to statistical variations in the projected number of stars per
pixel (used to determine the distance) from fluctuations from other
sources, which include photon noise, foreground stars, cosmic rays,
and the variations due to the overall structure of the galaxy. The
mean apparent magnitude of stars responsible for the measured
fluctuations is mI{bar}=29.78±0.03, with an additional systematic
uncertainty of 0.05mag. Using the latest calibration of Tonry
(1997ApJ...475..399T 1997ApJ...475..399T), we obtain a distance of 15.6±1.0Mpc, which is
consistent with the distance determined through the use of this method
in the infrared K band by Pahre & Mould (1994ApJ...433..567P 1994ApJ...433..567P). We
discuss the globular cluster (GC) luminosity function and color
distribution, based on the ∼130 candidates identified in the field. We
find a roughly Gaussian luminosity function centered at
mv=23.82±0.38 with σ=1.16±0.21. The GC color distribution
is also roughly Gaussian, centered at V-I=0.91±0.03, with
σ=0.20±0.03, and it is coincident to within the error bars
with the blue peak of the bimodal color distribution found in M87.
Comparing our data with recent evaluations of the GC color
distribution at two different locations in M87 we find a trend of the
red peak disappearing with radial distance. We speculate that this
could be understood if the blue portion of the M87 GC population were
acquired from its smaller companions. The specific frequency of
globular clusters is among the lowest for elliptical galaxies,
comparable only to the value found in M32. In both cases this may be a
result of tidal truncation by a giant neighbor. This further indicates
that clusters have been stripped from NGC 4478 by M87 and likely now
are part of its globular cluster population.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 39 132 Globular cluster candidate catalog
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- NTF97 [1/132]+ Sequential number
5- 6 I2 h RAh Right ascension (J2000)
8- 9 I2 min RAm Right ascension (J2000)
11- 15 F5.2 s RAs Right ascension (J2000)
17 A1 --- DE- Declination sign
18- 19 I2 deg DEd Declination (J2000)
21- 22 I2 arcmin DEm Declination (J2000)
24- 28 F5.2 arcsec DEs Declination (J2000)
30- 34 F5.2 mag Vmag V magnitude
36- 39 F4.2 mag V-I V-I colour index
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History: Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 12-May-1998