J/ApJ/805/65 FLAMES observations of NGC 5128's globular clusters (Taylor+, 2015)
Observational evidence for a dark side to NGC 5128's globular cluster system.
Taylor M.A., Puzia T.H., Gomez M., Woodley K.A.
<Astrophys. J., 805, 65 (2015)>
=2015ApJ...805...65T 2015ApJ...805...65T
ADC_Keywords: Clusters, globular ; Galaxies, nearby ; Spectroscopy ;
Radial velocities ; Velocity dispersion
Keywords: galaxies: individual: NGC 5128; galaxies: star clusters: general
Abstract:
We present a study of the dynamical properties of 125 compact stellar
systems (CSSs) in the nearby giant elliptical galaxy NGC 5128, using
high-resolution spectra (R∼26000) obtained with Very Large
Telescope/FLAMES. Our results provide evidence for a new type of star
cluster, based on the CSS dynamical mass scaling relations. All radial
velocity (vr) and line-of-sight velocity dispersion (σlos)
measurements are performed with the penalized pixel fitting (ppxf)
technique, which provided σppxf estimates for 115 targets. The
σppxf estimates are corrected to the 2D projected half-light
radii, σ1/2, as well as the cluster cores, σ0,
accounting for observational/aperture effects and are combined with
structural parameters, from high spatial resolution imaging, in order
to derive total dynamical masses (Mdyn) for 112 members of NGC5128's
star cluster system. In total, 89 CSSs have dynamical masses measured
for the first time along with the corresponding dynamical
mass-to-light ratios (σ1/2). We find two distinct sequences in
the γdynV-Mdyn plane, which are well approximated by power
laws of the forms γdynV∝Mdyn0.33±0.04 and
γdynV∝Mdyn0.79±0.04. The shallower sequence
corresponds to the very bright tail of the globular cluster luminosity
function (GCLF), while the steeper relation appears to be populated by
a distinct group of objects that require significant dark gravitating
components such as central massive black holes and/or exotically
concentrated dark matter distributions. This result would suggest that
the formation and evolution of these CSSs are markedly different from
the "classical" globular clusters in NGC 5128 and the Local Group,
despite the fact that these clusters have luminosities similar to the
GCLF turnover magnitude. We include a thorough discussion of myriad
factors potentially influencing our measurements.
Description:
During five nights in 2008 June/July, 123 of the brightest GCs around
NGC 5128 were observed using the Fiber Large Array Multi-Element
Spectrograph (FLAMES) instrument at the Very Large Telescope on Cerro
Paranal, Chile.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 60 140 Star cluster observations
table2.dat 138 140 Star cluster kinematics
table3.dat 125 140 Star cluster structural parameters
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See also:
J/ApJ/773/L36 : NGC 5128 globular cluster abundances (Colucci+, 2013)
J/AJ/143/84 : New candidate globular clusters in NGC 5128 (Harris+, 2012)
J/ApJS/197/22 : The Carnegie-Irvine Galaxy Survey (GGS). II. (Li+, 2011)
J/ApJS/192/10 : Chandra ACIS survey in 383 nearby galaxies. I. (Liu, 2011)
J/ApJ/726/108 : Dispersion-supported stellar systems (Tollerud+, 2011)
J/AJ/140/2101 : NGC 5128 globular clusters photometry (Sinnott+, 2010)
J/AJ/139/1871 : Kinematics of globulars in NGC 5128 (Woodley+, 2010)
J/ApJ/708/1335 : Spectroscopy of globulars in NGC 5128 (Woodley+, 2010)
J/ApJ/681/197 : ACS Virgo Cluster Survey. XV (Peng+, 2008)
J/MNRAS/386/1443 : 2dF study of globular clusters in NGC 5128 (Beasley+, 2008)
J/AJ/134/494 : NGC 5128 GCs UBVRICMT1 phot. + RV (Woodley+, 2007)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I04 --- GC [5/441] Cluster identifier (G1)
6- 7 I2 h RAh [13] Hour of Right Ascension (J2000)
9- 10 I2 min RAm [23/26] Minute of Right Ascension (J2000)
12- 17 F6.3 s RAs Second of Right Ascension (J2000)
19 A1 --- DE- [-] Sign of the Declination (J2000)
20- 21 I2 deg DEd [42/43] Degree of Declination (J2000)
23- 24 I2 arcmin DEm Arcminute of Declination (J2000)
26- 30 F5.2 arcsec DEs Arcsecond of Declination (J2000)
32- 36 F5.2 mag Rmag [17/20.5] Apparent R band magnitude (1)
38- 42 F5.2 mag Vmag [16.8/20.7] Dereddened apparent V band
magnitude (2)
44- 47 F4.2 mag e_Vmag [0.01/0.2] Uncertainty in Vmag
49- 53 I5 s Exp [1200/26400] Total integration time
55- 60 F6.2 --- S/N [0.2/11]?=-99 Signal-to-Noise ratio (3)
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Note (1): Used for target acquisition.
Note (2): Or r'-band magnitudes. Most of our sample objects have apparent
V-band magnitudes provided in the Woodley et al. (2007, J/AJ/134/494)
catalog (see also references therein). Where V-band magnitudes are
not available, we list de-reddened r'-band magnitudes from
Sinnott et al. (2010, J/AJ/140/2101). See section 3.6.
Note (3): See Section 2.2 for a definition. A "-99." indicates the S/N
could not be estimated because no radial velocity was able
to be obtained from the literature or our data.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I04 --- GC [5/441] Cluster identifier (G1)
6- 10 F5.2 arcmin Rgc [1/21.5] Galacto-centric angular radius
12- 14 I3 km/s RVlt [146/890]?=-99 Literature radial velocity
16- 18 I3 km/s e_RVlt [1/202]?=-99 Uncertainty in RVlt
20- 22 I3 km/s RV [19/836]?=-99 Penalized pixel fitting technique
radial velocity
24- 29 F6.2 km/s e_RV [0.3/31]?=-99 Uncertainty in RV
31- 36 F6.2 km/s sigma [1/68]?=-99 Penalized pixel fitting technique
velocity dispersion σ
38- 43 F6.2 km/s e_sigma [0.3/52]?=-99 Uncertainty in sigma
45- 51 F7.3 km/s sig.ap [3.6/68]?=-99 Model aperture corrected
velocity dispersion σap (4)
53- 59 F7.3 km/s E_sig.ap ?=-99 Upper uncertainty in sig.ap
61- 67 F7.3 km/s e_sig.ap ?=-99 Lower uncertainty in sig.ap
69- 75 F7.3 km/s sig.gl [3.5/62]?=-99 Global aperture corrected
velocity dispersion σgl
77- 83 F7.3 km/s E_sig.gl [0.02/18]?=-99 Upper uncertainty in sig.gl
85- 91 F7.3 km/s e_sig.gl [0.07/18]?=-99 Lower uncertainty in sig.gl
93- 98 F6.2 km/s sig.0 [4/69.2]?=-99 Cluster core aperture corrected
velocity dispersion σ0
100-106 F7.3 km/s E_sig.0 ?=-99 Upper uncertainty in sig.0
108-113 F6.2 km/s e_sig.0 ?=-99 Lower uncertainty in sig.0
115-120 F6.2 km/s sig.hl [3.9/66]?=-99 Aperature corrected 2D projected
half-light radius velocity dispersion
σ1/2
122-127 F6.2 km/s E_sig.hl ?=-99 Upper uncertainty in sig.hl
129-134 F6.2 km/s e_sig.hl ?=-99 Lower uncertainty in sig.hl
136-138 I3 --- r_RVlt [1/5]?=-99 Reference code for RVlt (5)
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Note (4): The model velocity dispersion corresponding to the FLAMES aperture.
Note (5): Reference as follows:
1 = Woodley et al. (2010, J/AJ/139/1871);
2 = Woodley et al. (2007, J/AJ/134/494), their mean;
3 = Woodley et al. (2007, J/AJ/134/494), LDSS2;
4 = Woodley et al. (2007, J/AJ/134/494), VIMOS;
5 = Woodley et al. (2007, J/AJ/134/494), Hydra.
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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- 4 I04 --- GC [5/441] Cluster identifier (G1)
6- 13 F8.4 Msun Mhm [0.03/7.5]?=-99 The 'half-mass' M1/2 (6)
15- 22 F8.4 Msun E_Mhm ?=-99 Upper limit uncertainty in Mhm
24- 31 F8.4 Msun e_Mhm ?=-99 Lower limit uncertainty in Mhm
33- 40 F8.4 Msun Mdyn [0.07/15.4]?=-99 Dynamical mass
42- 49 F8.4 Msun E_Mdyn ?=-99 Upper limit uncertainty in Mdyn
51- 58 F8.4 Msun e_Mdyn ?=-99 Lower limit uncertainty in Mdyn
60- 65 F6.2 Msun/Lsun M/Lhm [0.4/64.5]?=-99 The 'half-mass'
mass-to-light ratio
67- 72 F6.2 Msun/Lsun E_M/Lhm ?=-99 Upper limit uncertainty in M/Lhm
74- 79 F6.2 Msun/Lsun e_M/Lhm ?=-99 Lower limit uncertainty in M/Lhm
81- 86 F6.2 Msun/Lsun M/Ldyn [0.5/66.7]?=-99 Dynamic mass-to-light ratio
88- 93 F6.2 Msun/Lsun E_M/Ldyn ?=-99 Upper limit uncertainty in M/Ldyn
95-100 F6.2 Msun/Lsun e_M/Ldyn ?=-99 Lower limit uncertainty in M/Ldyn
102-107 F6.2 pc rh [0.2/23]?=-99 Half light radius
109-114 F6.2 pc e_rh ?=-99 Uncertainty in rh
116-121 F6.2 --- c [0.8/2.5]?=-99 Concentration parameter
123-125 I3 --- r_rh ?=-99 Reference for rh (7)
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Note (6): In other words the dynamical mass corresponding to that contained
within the 2D projected half-light radius.
Note (7): Reference as follows:
1 = Gomez et al. (2015, in prep.);
2 = Jordan et al. (2015, in prep.);
3 = Harris et al. (2002AJ....124.1435H 2002AJ....124.1435H).
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Global note:
Note (G1): "GC NNNN" clusters are named <[WHB2007] GCNNNN> in Simbad.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Sep-2015