J/ApJ/929/147 Luminous globular clusters in NGC 5128 (Dumont+, 2022)
A population of luminous globular clusters and stripped nuclei with elevated
mass to light ratios around NGC 5128.
Dumont A., Seth A.C., Strader J., Voggel K., Sand D.J., Hughes A.K.,
Caldwell N., Crnojevic D., Mateo M., Bailey J.I., Forbes D.A.
<Astrophys. J., 929, 147 (2022)>
=2022ApJ...929..147D 2022ApJ...929..147D
ADC_Keywords: Clusters, globular; Radial velocities; Spectra, optical;
Photometry, ugriz; Velocity dispersion; Black holes;
Magnitudes, absolute
Keywords: Ultracompact dwarf galaxies ; Globular star clusters ;
Mass-to-light ratio ; Galaxy nuclei ; Stellar kinematics ;
Stellar dynamics
Abstract:
The dense central regions of tidally disrupted galaxies can survive as
ultracompact dwarfs (UCDs) that hide among the luminous globular
clusters (GCs) in the halo of massive galaxies. An exciting
confirmation of this model is the detection of overmassive black holes
in the centers of some UCDs, which also lead to elevated dynamical
mass-to-light ratios (M/Ldyn). Here we present new high-resolution
spectroscopic observations of 321 luminous GC candidates in the
massive galaxy NGC 5128/Centaurus A. Using these data we confirm
27 new luminous GCs, and measure velocity dispersions for 57 luminous
GCs (with g-band luminosities between 2.5x105 and
2.5x107L☉), of which 48 are new measurements. Combining these
data with size measurements from Gaia, we determine the M/Ldyn for
all 57 luminous GCs. We see a clear bimodality in the M/Ldyn
distribution, with a population of normal GCs with mean
M/Ldyn=1.51±0.31, and a second population of ∼20 GCs with elevated
mean M/Ldyn=2.68±0.22. We show that black holes with masses
∼4%-18% of the luminous GCs can explain the elevated mass-to-light
ratios. Hence, it is plausible that the NGC 5128 sources with elevated
M/Ldyn are mostly stripped galaxy nuclei that contain massive
central black holes, though future high spatial resolution
observations are necessary to confirm this hypothesis for individual
sources. We also present a detailed discussion of an extreme outlier,
VHH81-01, one of the largest and most massive GC in NGC 5128, making
it an exceptionally strong candidate to be a tidally stripped nucleus.
Description:
The observations of 321 globular cluster (GC) candidates in Cen A were
taken over several observing runs between 2017 February and 2019 March
using the Michigan/Magellan Fiber System (M2FS) and the Magellan
Inamori Kyocera Echelle (MIKE) spectrograph at the 6.5m Magellan Clay
telescope at Las Campanas Observatory, Chile. M2FS is a fiber-fed
double spectrograph optimized to operate from 3700-9500Å (R∼25000).
MIKE is a single slit echelle, double arm spectrograph, delivering
full wavelength coverage from 3350-5000Å (blue) and 4900-9500Å
(red) (R∼22000). See Section 2.2.
Throughout this paper, we use photometry for our sources from the NOAO
DR2 source catalog (Nidever & Astro Data Lab team 2020ascl.soft12002N).
This photometry in ugriz is derived from DECam observations. We
present magnitudes corrected for galactic extinction using
Schlafly & Finkbeiner (2011ApJ...737..103S 2011ApJ...737..103S). See Section 2.1.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
13 25 27.61 -43 01 08.8 NGC 5128 = NAME Centaurus A
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 106 321 List of all observed luminous globular clusters
(GCs) candidates
table3.dat 122 57 List of 57 luminous GCs with visually verified
velocity dispersion
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See also:
II/371 : The Dark Energy Survey (DES): Data Release 2 (Abbott+, 2021)
J/A+AS/127/409 : New nearby dwarf galaxy candidates list (Karachentseva+ 1998)
J/A+AS/139/393 : Young Massive Star Clusters. II. (Larsen, 1999)
J/A+A/369/812 : UVKs phot. of globular clusters in NGC 5128 (Rejkuba, 2001)
J/A+A/407/1157 : UVES sky atlas (Hanuschik+, 2003)
J/AJ/128/723 : Washington Photometry in NGC 5128. II (Harris+, 2004)
J/ApJS/150/367 : Globular clusters in NGC 5128 (Peng+, 2004)
J/AJ/130/873 : Properties of BQS objects in the SDSS DR3 area (Jester+, 2005)
J/AJ/134/494 : NGC 5128 GCs UBVRICMT1 phot. & RV (Woodley+, 2007)
J/MNRAS/386/1443 : 2dF study of globular clusters in NGC 5128 (Beasley+, 2008)
J/MNRAS/392/879 : Globular clusters in nearby dwarf galaxies (Georgiev+, 2009)
J/ApJ/722/1373 : ω Centauri giants abundances (Johnson+, 2010)
J/ApJ/725/670 : Kinematics in the M32 nucleus (Seth, 2010)
J/AJ/139/1871 : Kinematics of globulars in NGC 5128 (Woodley+, 2010)
J/AJ/143/84 : New candidate globular clusters in NGC 5128 (Harris+, 2012)
J/ApJ/791/107 : Parameters of NGC 5139 SGBs stars (Villanova+, 2014)
J/ApJ/813/82 : z<0.06 broad-line AGN emission-line measures (Reines+, 2015)
J/ApJ/805/65 : FLAMES obs. of NGC 5128's globular clusters (Taylor+, 2015)
J/ApJ/850/15 : Mass-to-light ratios in early-type galaxies (Pechetti+, 2017)
J/MNRAS/469/3444 : Centaurus A's Baryonic Structures II. (Taylor+, 2017)
J/ApJ/858/102 : Gemini/NIFS and HST obs. of the galaxy M59-UCD3 (Ahn+, 2018)
J/ApJ/858/118 : Kinematic data of 3 nearby low-mass galaxies (Nguyen+, 2018)
J/ApJ/899/140 : 632 Gaia Ultracompact Dwarf galaxy candidates (Voggel+, 2020)
J/ApJ/914/16 : NGC 5128 GCs from PISCes, Gaia DR2 and NSC (Hughes+, 2021)
J/A+A/649/A3 : Gaia EDR3 photometric passbands (Riello+, 2021)
http://datalab.noirlab.edu/nscdr2 : NOIRLab Source Catalog (NSC) homepage
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 A17 --- ID Discovery identifier (G1)
19- 33 A15 --- r_ID Reference for ID (1)
35- 44 F10.6 deg RAdeg [198.28/203.54] Right Ascension (J2000)
46- 55 F10.6 deg DEdeg [-45.22/-41.3] Declination (J2000)
57- 61 F5.2 --- S/N [0.78/52.5]? Signal-to-Noise
63- 67 F5.2 mag g0mag [14.63/23.42]? Intrinsic NOAO DR2 g band AB
magnitude
69- 74 F6.1 km/s RVel [-147/903]? Heliocentric radial velocity
76- 80 F5.1 km/s e_RVel [2.4/158]? Uncertainty in RVel
82- 85 F4.2 [-] Z [0/2]? Derived luminosity-weighted metallicity
87- 90 F4.2 [-] e_Z [0.3/0.4]? Uncertainty in Z
92- 98 A7 --- setup Instrument and setup used (G2)
100 A1 --- Mm Candidate has RVel expected for Cen A GC? (2)
102-106 A5 --- Ref Literature source of candidate (G3)
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Note (1): Literature reference for the target ID as follows:
Beasley2008 = Beasley et al. 2008, J/MNRAS/386/1443
Berg1981 = van den Bergh et al. 1981AJ.....86...24V 1981AJ.....86...24V
Gomez2006 = Gomez et al. 2006A&A...447..877G 2006A&A...447..877G
Harris1992 = Harris et al. 1992AJ....104..613H 1992AJ....104..613H
Harris2004 = Harris et al. 2004, J/AJ/128/723
Harris2012 = Harris et al. 2012, J/AJ/143/84
Hesser1986 = Hesser et al. 1986ApJ...303L..51H 1986ApJ...303L..51H
Kraft2001 = Kraft et al. 2001, J/ApJ/560/675
Peng2004 = Peng et al. 2004, J/ApJS/150/367
Rejkuba2001 = Rejkuba M. 2001, J/A+A/369/812
Taylor2017 = Taylor et al. 2017, J/MNRAS/469/3444
Voggel2020 = Voggel et al. 2020, J/ApJ/899/140
Woodley2005 = Woodley et al. 2005AJ....129.2654W 2005AJ....129.2654W
Woodley2007 = Woodley et al. 2007, J/AJ/134/494
Woodley2010 = Woodley et al. 2010, J/AJ/139/1871
This Work = Dumont et al. 2022ApJ...929..147D 2022ApJ...929..147D (this catalog)
Note (2): Code as follows:
Y = Cen A object: is consistent with RVel>250km/s (see Figure 1;
78 occurrences)
N = radial velocity consistent with Milky Way foreground star
(141 occurrences).
For NULL values, we cannot reliably determine its radial velocity.
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- ID Discovery identifier (G1)
12 A1 --- f_ID [*] Flag on ID (1)
14- 18 F5.1 km/s RVel [280/903] Heliocentric radial velocity
20- 23 F4.2 km/s e_RVel [2.4/6.1] Uncertainty in RVel
25- 29 F5.2 km/s sigma [6.5/22] Derived velocity dispersion
31- 34 F4.2 km/s e_sigma [0.8/5] Uncertainty in sigma
36- 40 F5.2 km/s sigmaGl [5.8/21.5] Global velocity dispersion;
See Section 5
42- 48 A7 --- setup Instrument and setup used (G2)
50- 55 F6.4 arcsec rhm [0.13/1.8] Calculated half-mass radius
57- 67 A11 --- r_rhm Reference for rhm (2)
69- 74 F6.2 mag VMag [-11.1/-8.6] Absolute V band Vega magnitude (3)
76- 80 F5.3 mag E(B-V) [0.08/0.2] Color excess in (B-V) used for Vmag
82- 85 F4.2 Sun M/LV [0.8/7.2] V band mass-to-light ratio
87- 90 F4.2 Sun E_M/LV [0.2/1.2] Upper uncertainty in M/LV
92- 95 F4.2 Sun e_M/LV [0.18/1.1] Lower uncertainty in M/LV
97- 102 E6.2 Msun BHMass [76000/861000]? Predicted Black Hole mass (4)
104- 109 E6.2 Msun E_BHMass [90000/1030000]? Upper uncertainty in BHMass
111- 116 E6.2 Msun e_BHMass [12000/174000]? Lower uncertainty in BHMass
118- 122 A5 --- Ref Literature source of candidate (G3)
-------------------------------------------------------------------------------
Note (1): Flag as follows:
* = One of two luminous GCs with probably incorrect V-band
luminosity (See Section 4).
Note (2): With "Gaia" being the BRexcess-half-mass radii relation described
in Section 4, and M08/ACS and M08/STIS are sizes from
McLaughlin+ 2008MNRAS.384..563M 2008MNRAS.384..563M
Note (3): Extinction corrected and assuming a V band distance modulus
of (m-M)=27.91.
Note (4): Necessary for luminous GCs with M/LV≥2.3 to reproduce
the observed elevated M/LV .
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Global notes:
Note (G1): For 133 targets that were based on preliminary versions of
Voggel+ (2020, J/ApJ/899/140), Hughes+ (2021, J/ApJ/914/16) and do not
have literature names, we name them as GC_cand with numbers running
from 1 to 133.
Note (G2): with "ca" & "mg" being Calcium & Magnesium triplet respectively.
For targets observed with MIKE, only the Calcium Triplet measurements
are shown in this table.
Note (G3): Source as follows:
A = most likely Cen A GC from Voggel+ (2020, J/ApJ/899/140),
B = good candidate Cen A GC from Voggel+ (2020, J/ApJ/899/140),
C = candidate Cen A GC from Voggel+ (2020, J/ApJ/899/140)
RV = previous literature measured radial velocity from
Harris+ (2002AJ....124.1435H 2002AJ....124.1435H); Peng+ (2004, J/ApJS/150/367);
Martini & Ho (2004ApJ...610..233M 2004ApJ...610..233M); Rejkuba+ (2007A&A...469..147R 2007A&A...469..147R);
Taylor+ (2010ApJ...712.1191T 2010ApJ...712.1191T or 2015, J/ApJ/805/65)
Sigma = previous literature velocity dispersion measurement from
Harris+ (2002AJ....124.1435H 2002AJ....124.1435H); Peng+ (2004, J/ApJS/150/367);
Martini & Ho (2004ApJ...610..233M 2004ApJ...610..233M); Rejkuba+ (2007A&A...469..147R 2007A&A...469..147R);
Taylor+ (2010ApJ...712.1191T 2010ApJ...712.1191T or 2015, J/ApJ/805/65)
New = targets that are not in KV20 (Voggel+ 2020, J/ApJ/899/140) catalog,
and have no previous literature kinematic measurements
(123 occurrences)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 12-Mar-2024