J/MNRAS/446/369 Colour and spectral index from the SLUGGS survey (Usher+, 2015)
The SLUGGS survey: globular cluster stellar population trends from weak
absorption lines in stacked spectra.
Usher C., Forbes D.A., Brodie J.P., Romanowsky A.J., Strader J., Conroy C.,
Foster C., Pastorello N., Pota V., Arnold J.A.
<Mon. Not. R. Astron. Soc., 446, 369-390 (2015)>
=2015MNRAS.446..369U 2015MNRAS.446..369U (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Clusters, globular ; Populations, stellar ;
Colors ; Magnitudes, absolute ; Spectroscopy ; Surveys
Keywords: globular clusters: general - galaxies: abundances -
galaxies: star clusters: general - galaxies: stellar content
Abstract:
As part of the SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS)
survey, we stack 1137 Keck DEIMOS (Deep Imaging Multi-Object
Spectrograph) spectra of globular clusters from 10 galaxies to study
their stellar populations in detail. The stacked spectra have median
signal-to-noise ratios of ∼90 Å-1. Besides the calcium triplet, we
study weaker sodium, magnesium, titanium and iron lines as well as the
Hα and higher order Paschen hydrogen lines. In general, the
stacked spectra are consistent with old ages and a Milky Way-like
initial mass function. However, we see different metal line index
strengths at fixed colour and magnitude, and differences in the
calcium triplet-colour relation from galaxy to galaxy. We interpret
this as strong evidence for variations in the globular cluster
colour-metallicity relation between galaxies. Two possible
explanations for the colour-metallicity relation variations are that
the average ages of globular clusters vary from galaxy to galaxy or
that the average abundances of light elements (i.e. He, C, N and O)
differ between galaxies. Stacking spectra by magnitude, we see that
the colours become redder and metal line indices stronger with
brighter magnitudes. These trends are consistent with the previously
reported `blue tilts' being mass-metallicity relations.
Description:
The SLUGGS survey is an ongoing study of 25 massive, nearby,
early-type galaxies and their GC systems using Keck DEIMOS
spectroscopy and wide-field imaging from Suprime-Cam (Miyazaki et al.
2002, PASJ, 54, 833) on the Subaru telescope. The spectra were all
observed with DEIMOS in multislit mode between 2006 and 2013 with the
primary aim of measuring GC radial velocities. Exposure times averaged
two hours per slit mask. All observations used a central wavelength of
7800 Å, the 1200 line/mm grating and 1 arcsec slits. This setup
yields a resolution of Δλ∼1.5 Å and covers the Na I
doublet to CaT wavelength region. In roughly half of the slits, Hα
is also covered.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 58 10 Galaxy properties
tablea1.dat 201 45 Colour and spectral index measurements of
spectra stacked by colour for galaxies
tablea2.dat 201 20 Colour and spectral index measurements of
spectra stacked by colour for groups
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See also:
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/MNRAS/355/608 : NGC 4649 (M60) globular clusters (Forbes+, 2004)
J/A+A/455/453 : Globular Cluster System of NGC5846 (Chies-Santos+, 2006)
J/ApJ/655/144 : ACS Virgo Cluster Survey. XIII. (Mei+, 2007)
J/AJ/137/4956 : Globular clusters around NGC 1407 (Romanowsky+, 2009)
J/MNRAS/413/813 : ATLAS3D project. I. (Cappellari+, 2011)
J/MNRAS/420/37 : NGC 4365 globular clusters (Blom+, 2012)
J/MNRAS/426/1475 : CaT in 903 globular clusters (Usher+, 2012)
J/MNRAS/428/389 : SLUGGS globular clusters in early-type galaxies
(Pota+, 2013)
J/MNRAS/436/1172 : Globular Clusters of NGC 4278 in SLUGGS (Usher+, 2013)
J/AJ/148/32 : Globular cluster candidates in NGC 3115 (Jennings+, 2014)
J/MNRAS/452/2208 : NGC 4473 globular clusters (Alabi+, 2015)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- --- [NGC]
4- 7 I4 --- NGC [1407/5846] Host galaxy name
8 A1 --- n_NGC [a] Note on NGC (1)
10- 11 I2 h RAh Simbad Hour of Right Ascension (J2000)
13- 14 I2 min RAm Simbad Minute of Right Ascension (J2000)
16- 21 F6.3 s RAs Simbad Second of Right Ascension (J2000)
23 A1 --- DE- Simbad Sign of the Declination (J2000)
24- 25 I2 deg DEd Simbad Degree of Declination (J2000)
27- 28 I2 arcmin DEm Simbad Arcminute of Declination (J2000)
30- 34 F5.2 arcsec DEs Simbad Arcsecond of Declination (J2000)
36- 39 I4 km/s Vsys Systemic velocity from Cappellari et al.
(2011, J/MNRAS/413/813)
41- 44 F4.1 Mpc Dist Distance from Cappellari et al.
(2011, J/MNRAS/413/813) (2)
46- 50 F5.1 mag KMag K-band absolute magnitude from
Cappellari et al. (2011, J/MNRAS/413/813) (3)
52- 54 I3 --- Spectra Total number of GC spectra
56- 58 I3 --- GC Number of unique GCs with spectra
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Note (1): NGC 1407 and NGC 3115 are not part of the Cappellari et al.
(2011, J/MNRAS/413/813) sample so their radial velocities were taken
from NED while their distances are from Tonry et al.
(2001ApJ...546..681T 2001ApJ...546..681T) with the same -0.06 mag distance moduli offset
as Cappellari et al. (2011, J/MNRAS/413/813).
We assume that NGC 1400 and NGC 1407 are part of the same group and
use the mean of their distance moduli for NGC 1407. Their K-band
absolute magnitude is also calculated from the 2MASS total K apparent
magnitude and the distance in the same manner as Cappellari et al.
(2011, J/MNRAS/413/813).
Note (2): Based on surface brightness fluctuations (SBF) of Tonry et al.
(2001ApJ...546..681T 2001ApJ...546..681T). For NGC 4365, NGC 4473 and NGC 4649,
Cappellari et al. (2011, J/MNRAS/413/813) used the SBF distance of
Mei et al. (2007, J/ApJ/655/144).
Note (3): Calculated from the 2MASS (Skrutskie et al. 2006, Cat. VII/233) total
K-band apparent magnitude and the distance in the previous column,
corrected for foreground extinction.
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Byte-by-byte Description of file: tablea1.dat tablea2.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Group [faint bright] Galaxy group (1)
8- 10 A3 --- --- [NGC]
11- 14 I4 --- NGC [1407/5846]? Host galaxy name
16- 21 F6.4 mag g-i Subaru/Suprime-Cam (g-i) colour index
23- 28 F6.4 mag E_g-i Upper limit uncertainty in g-i
30- 35 F6.4 mag e_g-i Lower limit uncertainty in g-i
37- 43 F7.3 mag iMag Subaru/Suprime-Cam i-band absolute magnitude
45- 49 F5.3 mag E_iMag Upper limit uncertainty in iMag
51- 55 F5.3 mag e_iMag Lower limit uncertainty in iMag
57- 61 F5.3 0.1nm CaT Ca II triplet spectral index strength (Å)
63- 67 F5.3 0.1nm E_CaT Upper limit uncertainty in CaT
69- 73 F5.3 0.1nm e_CaT Lower limit uncertainty in CaT
75- 79 F5.3 0.1nm Fe86 Fe86 spectral index strength (Å)
81- 85 F5.3 0.1nm E_Fe86 Upper limit uncertainty in Fe86
87- 91 F5.3 0.1nm e_Fe86 Lower limit uncertainty in Fe86
93- 97 F5.3 0.1nm Mg88 Mg88 spectral index strength (Å)
99-103 F5.3 0.1nm E_Mg88 Upper limit uncertainty in Mg88
105-109 F5.3 0.1nm e_Mg88 Lower limit uncertainty in Mg88
111-116 F6.3 0.1nm Na82 Na82 spectral index strength (Å)
118-122 F5.3 0.1nm E_Na82 Upper limit uncertainty in Na82
124-128 F5.3 0.1nm e_Na82 Lower limit uncertainty in Na82
130-135 F6.4 --- TiO89 TiO89 spectral index strength
137-142 F6.4 --- E_TiO89 Upper limit uncertainty in TiO89
144-149 F6.4 --- e_TiO89 Lower limit uncertainty in TiO89
151-155 F5.3 0.1nm Halpha Hα spectral index strength (Å)
157-161 F5.3 0.1nm E_Halpha Upper limit uncertainty in Halpha
163-167 F5.3 0.1nm e_Halpha Lower limit uncertainty in Halpha
169-173 F5.3 0.1nm PaT Paschen line spectral index strength (Å)
175-179 F5.3 0.1nm E_PaT Upper limit uncertainty in PaT
181-185 F5.3 0.1nm e_PaT Lower limit uncertainty in PaT
187-191 F5.2 km/s sigma ? Velocity dispersion
193-196 F4.2 km/s E_sigma ? Upper limit uncertainty in sigma
198-201 F4.2 km/s e_sigma ? Lower limit uncertainty in sigma
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Note (1): NGC 1407, NGC 4278, NGC 4365 and NGC 4649 are in the bright group;
NGC 3115, NGC 3377, NGC 4473 and NGC 4494 are in the faint group.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 30-Oct-2017