TY - JOUR
T1 - Dynamical masses and mass-to-light ratios of resolved massive star clusters – I. NGC 419 and NGC 1846
AU - Song, Ying Yi
AU - Mateo, Mario
AU - Mackey, A. D.
AU - Olszewski, Edward W.
AU - Roederer, Ian U.
AU - Walker, Matthew G.
AU - Bailey, John I.
N1 - Funding Information:
We thank the anonymous referee for helpful comments. MM and Y-YS are supported by National Science Foundation (NSF) grants AST-1312997 and AST-1815403. EO is partially supported by NSF grant AST-1815767. IUR acknowledges support from NSF grants AST-1613536, AST-1815403, and PHY 14-30152 (Physics Frontier Center/JINA-CEE). MGW is partially supported by NSF grant AST-1813881. We thank Jeff Crane, Steve Shectman, and Ian Thompson for invaluable contributions to the design, construction, and support of M2FS. We thank the M2FS Team for obtaining the spectroscopic data at the Magellan/Clay telescope, especially Anthony Kremin and Meghin Spencer for the data of NGC 419, and Daniela Barrientos, Valentino Gonzalez, and Terese Hansen for the data of NGC 1846. This paper includes data gathered with the 6.5-metre Magellan Telescopes located at Las Campanas Observatory, Chile.
Publisher Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2019/11/21
Y1 - 2019/11/21
N2 - 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 singlemass 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 −0.21 km s−1, corresponding to a total mass of 7.6+2.5 −1.3 × 104 M 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 −0.24 km s−1, 5.4+1.5 −1.4 × 104 M, 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..
AB - 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 singlemass 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 −0.21 km s−1, corresponding to a total mass of 7.6+2.5 −1.3 × 104 M 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 −0.24 km s−1, 5.4+1.5 −1.4 × 104 M, 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..
KW - Galaxies: star clusters: individual: NGC 419 and NGC 1846
KW - Magellanic Clouds
KW - Stars: abundances
KW - Stars: kinematics and dynamics
KW - Techniques: spectroscopic
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U2 - 10.1093/mnras/stz2502
DO - 10.1093/mnras/stz2502
M3 - Article
AN - SCOPUS:85075243536
SN - 0035-8711
VL - 490
SP - 385
EP - 407
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 1
ER -