J/MNRAS/490/385 Massive star clusters NGC 419 and NGC 1846 (Song+, 2019)
Dynamical masses and mass-to-light ratios of resolved massive star clusters.
I. NGC 419 and NGC 1846.
Song Y.-Y., Mateo M., Mackey A.D., Olszewski E.W., Roederer I.U.,
Walker M.G., Bailey J.I.
<Mon. Not. R. Astron. Soc., 490, 385-407 (2019)>
=2019MNRAS.490..385S 2019MNRAS.490..385S (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Magellanic Clouds ; Radial velocities ;
Photometry, VRI ; Spectra, optical
Keywords: techniques: spectroscopic - stars: kinematics and dynamics -
stars: abundances - Magellanic Clouds -
galaxies: star clusters: individual: NGC 419 and NGC 1846
Abstract:
As an introduction of a kinematic survey of Magellanic Cloud (MC) star
clusters, we report on the dynamical masses and mass-to-light ratios
(M/L) of NGC 419 (Small Magellanic Cloud) and NGC 1846 (Large
Magellanic Cloud). We have obtained more than one hundred
high-resolution stellar spectra in and around each cluster using the
multi-object spectrograph M2FS on the Magellan/Clay Telescope.
Line-of-sight velocities and positions of the stars observed in each
cluster were used as input to an expectation-maximization algorithm
used to estimate cluster membership probabilities, resulting in
samples of 46 and 52 likely members (PM≥50 per cent) in NGC 419 and
NGC 1846, respectively. This process employed single-mass King models
constrained by the structural parameters of the clusters and provided
self-consistent dynamical mass estimates for both clusters. Our
best-fitting results show that NGC 419 has a projected central
velocity dispersion of 2.44+0.37-0.21km/s, corresponding to a
total mass of 7.6+2.5-1.3x104M☉ and V-band M/L ratio of
0.22+0.08-0.05 in solar units. For NGC 1846, the corresponding
results are 2.04+0.28-0.24km/s, 5.4+1.5-1.4x104M☉, and
0.32+0.11-0.11. The mean metallicities of NGC 419 and NGC 1846 are
found to be [Fe/H]=-0.84±0.19 and -0.70±0.08, respectively, based
on the spectra of likely cluster members. We find marginal statistical
evidence of rotation in both clusters, though in neither cluster does
rotation alter our mass estimates significantly. We critically compare
our findings with those of previous kinematic studies of these two
clusters in order to evaluate the consistency of our observational
results and analytic tools.
Description:
The clusters identified for use in the present papers and for all
future papers of our study were chosen from catalogues of Magellanic
Clouds clusters with good-quality age and metallicity estimates and
for which we could expect to obtain samples of about 50 stellar
members.
For NGC 419 and NGC 1846 we used the HST images from GO-10396 (NGC
419; PI: Gallagher) and from GO-10595 (NGC 1846; PI: Goudfrooij) to
identify stars in the cluster centres. Both programs obtained
relatively short exposures with the F555W and F814W filters (i.e. 40
and 20s for NGC 419, while 41 and 9s for NGC 1846). We photometered
all the images using the ACS modules from the DOLPHOT package (Dolphin
2000PASP..112.1383D 2000PASP..112.1383D), and the output magnitudes were automatically
transformed into the standard Johnson-Cousins VI system. The targets
were mainly selected from the RGB in the corresponding (V-I, V) CMDs.
For both clusters, the field stars were drawn from the Magellanic
Clouds Photometric Survey (MCPS) UBVI catalogue (Zaritsky et al.
2002AJ....123..855Z 2002AJ....123..855Z, Cat. J/AJ/123/855, 2004AJ....128.1606Z 2004AJ....128.1606Z, Cat.
J/AJ/128/1606).
The spectral data used in this paper has been obtained with the M2FS.
This instrument can deploy up to 256 optical fibers in a 29-arcmin
diameter field using aluminium plugplates pre-drilled for each target.
The spectrograph in M2FS (MSpec) consists of twin spectrographs
(denoted 'B' and 'R'), each capable of observing 128 targets
simultaneously over selected regions within the spectral range
3700-9500Å.
Objects:
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RA (ICRS) DE Designation(s)
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01 08 17.79 -72 53 02.7 NGC419 = Cl Kron 58 = Cl Lindsay 85 = LI-SMC 182
05 07 34.89 -67 27 32.4 NGC1846 = ESO 56-67 = KMHK 557 = OGLE-CL LMC 128
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File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table4.dat 79 111 M2FS Sample of NGC 419
table5.dat 85 196 Combined Sample of NGC 1846
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See also:
J/AJ/123/855 : Magellanic Clouds Photometric Survey: the SMC
(Zaritsky+, 2002)
J/AJ/128/1606 : Magellanic Clouds Photometric Survey: the LMC
(Zaritsky+, 2004)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Name Star name (N419-1-aNNN)
13- 14 I2 h RAh Right ascension (J2000)
16- 17 I2 min RAm Right ascension (J2000)
19- 23 F5.2 s RAs Right ascension (J2000)
25 A1 --- DE- Declination sign (J2000)
26- 27 I2 deg DEd Declination (J2000)
29- 30 I2 arcmin DEm Declination (J2000)
32- 35 F4.1 arcsec DEs Declination (J2000)
37- 42 F6.3 mag Vmag V-band magnitude
44- 48 F5.3 mag e_Vmag Error on Vmag
50- 54 F5.3 mag V-I V-I colour index
56- 60 F5.3 mag e_V-I Error on V-I
62- 67 F6.2 km/s vLOS Barycentric line of sight velocity
69- 72 F4.2 km/s e_vLOS Error on vLOS
74- 77 F4.2 --- PMi Normalized cluster-membership probability
79 A1 --- Sel [H/M] Photometric source (1)
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Note (1): Photometric source as follows:
H = Hubble Space Telescope (HST) photometry
M = Magellanic Clouds Photometric Survey (MCPS) photometry from
Zaritsky et al. (2002AJ....123..855Z 2002AJ....123..855Z, Cat. J/AJ/123/855)
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Name Star name (ACS-NNN-A, MCPS-NNN,
N1846-1-bNNN or N1846-1-rNNN)
14- 15 I2 h RAh Right ascension (J2000)
17- 18 I2 min RAm Right ascension (J2000)
20- 24 F5.2 s RAs Right ascension (J2000)
26 A1 --- DE- Declination sign (J2000)
27- 28 I2 deg DEd Declination (J2000)
30- 31 I2 arcmin DEm Declination (J2000)
33- 36 F4.1 arcsec DEs Declination (J2000)
38- 43 F6.3 mag Vmag ? V-band magnitude
45- 49 F5.3 mag e_Vmag ? Error on Vmag
51- 55 F5.3 mag V-I ? V-I colour index
57- 61 F5.3 mag e_V-I ? Error on V-I
63- 68 F6.2 km/s vLOS Barycentric line of sight velocity
70- 73 F4.2 km/s e_vLOS Error on vLOS
75- 78 F4.2 --- PMi Normalized cluster-membership probability
80 A1 --- Sel [H/M] Photometric source (1)
82- 85 A4 --- Spec Spectroscopic source of the LOS velocity (2)
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Note (1): Photometric source as follows:
H = Hubble Space Telescope (HST) photometry
M = Magellanic Clouds Photometric Survey (MCPS) photometry from
Zaritsky et al. (2004AJ....128.1606Z 2004AJ....128.1606Z, Cat. J/AJ/128/1606)
Note (2): Spectroscopic source as follows:
M2FS = M2FS observations from this work
M13 = Mackey et al. (2013ApJ...762...65M 2013ApJ...762...65M), data obtained using the MOS FLAMES
mounted at the ESO Very Large Telescope
COMB = Combined
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 24-Jan-2023