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
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:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
1- 4 I04 --- GC [5/441] Cluster identifier (G1) 6- 7 I2 h RAh  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)
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.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
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)
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.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
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)
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).
Global note: Note (G1): "GC NNNN" clusters are named <[WHB2007] GCNNNN> in Simbad.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Sep-2015
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