J/MNRAS/417/1823 Sombrero galaxy globular clusters (Alves-Brito+, 2011)
Spectra of globular clusters in the Sombrero galaxy:
evidence for spectroscopic metallicity bimodality.
Alves-Brito A., Hau G.K.T., Forbes D.A., Spitler L.R., Strader J.,
Brodie J.P., Rhode K.L.
<Mon. Not. R. Astron. Soc., 417, 1823-1838 (2011)>
=2011MNRAS.417.1823A 2011MNRAS.417.1823A (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Radial velocities ; Photometry, UBVRI ;
Abundances, [Fe/H] ; Morphology
Keywords: globular clusters: general -
galaxies: individual: Sombrero (M104, NGC 4594) -
galaxies: star clusters: general
Abstract:
We present a large sample of over 200 integrated-light spectra of
confirmed globular clusters (GCs) associated with the Sombrero (M104)
galaxy taken with the Deep Imaging Multi-Object Spectrograph (DEIMOS)
instrument on the Keck telescope. A significant fraction of the
spectra have signal-to-noise ratio levels high enough to allow
measurements of GC metallicities using the method of Brodie & Huchra.
We find a distribution of spectroscopic metallicities in the range
-2.2<[Fe/H]<+0.1 that is bimodal, with peaks at [Fe/H]~-1.4 and -0.6.
Thus, the GC system of the Sombrero galaxy, like a few other galaxies
now studied in detail, reveals a bimodal spectroscopic metallicity
distribution supporting the long-held belief that colour bimodality
reflects two metallicity subpopulations. This further suggests that
the transformation from optical colour to metallicity for old stellar
populations, such as GCs, is not strongly non-linear. We also explore
the radial and magnitude distribution with metallicity for GC
subpopulations but small number statistics prevent any clear trends in
these distributions.
Description:
GC candidates were selected from two published photometric studies. In
the inner regions we used the BVR Hubble Space Telescope
(HST)/Advanced Camera for Surveys (ACS) mosaic of Spitler et al.
(2006, Cat. J/AJ/132/1593), which covers approximately the central
10x7-arcmin2 of the galaxy with minimal contamination. Beyond this
area, we used the ground-based BVR catalogue of Rhode & Zepf
(2004AJ....127..302R 2004AJ....127..302R). This latter catalogue has higher contamination
but extends to the apparent edge of the GC system at a projected
radius of 19 arcmin and so is necessary to complement the wide field
of view (16x5arcmin2) of the DEIMOS spectrograph. The central dust
lane of NGC 4594 was excluded from our target selection.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 68 259 IDs, positions and velocities for the sample.
tableb1.dat 119 250 IDs, magnitudes, colours, indices and
metallicities for the GC candidate sample
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See also:
J/AJ/132/1593 : BVR photometry of NGC 4594 globular clusters (Spitler+, 2006)
J/ApJ/658/980 : New velocities for 62 M104 globular clusters (Bridges+, 2007)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- ID Name (RZNNNN or SNNN),
[RZ2004] GCl NNNN or [SLS2006] NNN in Simbab
8- 11 A4 --- OName Alternative ID (SNNN)
13 I1 --- Mask [1/4] Mask number
15- 16 I2 h RAh Right ascension (J2000)
18- 19 I2 min RAm Right ascension (J2000)
21- 25 F5.2 s RAs Right ascension (J2000)
27 A1 --- DE- Declination sign (J2000)
28- 29 I2 deg DEd Declination (J2000)
31- 32 I2 arcmin DEm Declination (J2000)
34- 38 F5.2 arcsec DEs Declination (J2000)
40- 45 F6.3 arcmin Maj Major axis
47- 52 F6.3 arcmin Min Major axis
54- 59 F6.3 arcmin Rp Projected distance from the centre of the galaxy
61- 64 I4 km/s RV Radial velocity
66- 68 I3 km/s e_RV rms uncertainty on RV
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Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- ID Name (RZNNNN or SNNN)
8- 11 A4 --- OName Alternative ID (SNNN)
13- 17 F5.2 mag Vmag V magnitude
19- 22 F4.2 mag B-R B-R colour index
24- 29 F6.3 --- CH CH index
31- 35 F5.3 --- e_CH ?=- rms uncertainty on CH
38- 43 F6.3 [-] [Fe/H]CH ? Metallicity [Fe/H] from CH index
45- 49 F5.3 [-] e_[Fe/H]CH ?=- rms uncertainty on [Fe/H]CH
52- 57 F6.3 --- Mgb ?=- Mgb index
59- 63 F5.3 --- e_Mgb ?=- rms uncertainty on Mgb
66- 71 F6.3 [-] [Fe/H]Mgb ?=- Metallicity [Fe/H] from Mgb index
73- 77 F5.3 [-] e_[Fe/H]Mgb ?=- rms uncertainty on [Fe/H]Mgb
80- 85 F6.3 --- Fe5270 ? Fe5270 index
87- 91 F5.3 --- e_Fe5270 ?=- rms uncertainty on Fe5270
94- 99 F6.3 [-] [Fe/H]Fe5270 ? Metallicity [Fe/H] from Fe5270 index
101-105 F5.3 [-] e_[Fe/H]Fe5270 ?=- rms uncertainty on [Fe/H]Fe5270
108-113 F6.3 [-] [Fe/H] ? Final metallicity [Fe/H]
115-119 F5.3 [-] e_[Fe/H] ?=- rms uncertainty on [Fe/H]
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 29-Jan-2018