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- ItemSimulating Globular Clusters in Dark Matter Subhalos(London : Institute of Physics Publ., 2022) Carlberg, Raymond G.; Keating, Laura C.A cosmological zoom-in simulation that develops into a Milky Way-like halo begins at redshift 7. The initial dark matter distribution is seeded with dense star clusters of median mass 5 × 105 M o˙, placed in the largest subhalos present, which have a median peak circular velocity of 25 km s-1. Three simulations are initialized using the same dark matter distribution with the star clusters starting on approximately circular orbits having initial median radii 6.8, 0.14 kpc, and, at the exact center of the subhalos. The simulations are evolved to the current epoch at which time the median galactic orbital radii of the three sets of clusters are 30, 5, and 16 kpc, with the clusters losing about 2%, 50%, and 15% of their mass, respectively. Clusters beginning at small orbital radii have so much tidal forcing that they are often not in equilibrium. Clusters that start at larger subhalo radii have a velocity dispersion that declines smoothly to ≃20% of the central value at ≃20 half-mass radii. The clusters that begin in the subhalo centers can show a rise in velocity dispersion beyond 3-5 half-mass radii. That is, the clusters that form without local dark matter always have stellar-mass-dominated kinematics at all radii, whereas about 25% of the clusters that begin in subhalo centers have remnant local dark matter.
- ItemDetection of a 100,000 M-circle dot black hole in M31's Most Massive Globular Cluster: A Tidally Stripped Nucleus(London : Institute of Physics Publ., 2022) Pechetti, Renuka; Seth, Anil; Kamann, Sebastian; Caldwell, Nelson; Strader, Jay; den Brok, Mark; Luetzgendorf, Nora; Neumayer, Nadine; Voggel, KarinaWe investigate the presence of a central black hole (BH) in B023-G078, M31's most massive globular cluster. We present high-resolution, adaptive-optics assisted, integral-field spectroscopic kinematics from Gemini/NIFS that show a strong rotation (∼20 km s-1) and a velocity dispersion rise toward the center (37 km s-1). We combine the kinematic data with a mass model based on a two-component fit to HST ACS/HRC data of the cluster to estimate the mass of a putative BH. Our dynamical modeling suggests a >3σ detection of a BH component of (1σ uncertainties). The inferred stellar mass of the cluster is , consistent with previous estimates, thus the BH makes up 1.5% of its mass. We examine whether the observed kinematics are caused by a collection of stellar mass BHs by modeling an extended dark mass as a Plummer profile. The upper limit on the size scale of the extended mass is 0.56 pc (95% confidence), which does not rule out an extended mass. There is compelling evidence that B023-G078 is the tidally stripped nucleus of a galaxy with a stellar mass >109 M o˙, including its high-mass, two-component luminosity profile, color, metallicity gradient, and spread in metallicity. Given the emerging evidence that the central BH occupation fraction of >109 M o˙ galaxies is high, the most plausible interpretation of the kinematic data is that B023-G078 hosts a central BH. This makes it the strongest BH detection in a lower-mass (<107 M o˙) stripped nucleus, and one of the few dynamically detected intermediate-mass BHs.
- ItemA Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. III. Discrete Multicomponent Population-dynamical Models Based on the Jeans Equations(London : Institute of Physics Publ., 2022) Kacharov, Nikolay; Alfaro-Cuello, Mayte; Neumayer, Nadine; Lützgendorf, Nora; Watkins, Laura L.; Mastrobuono-Battisti, Alessandra; Kamann, Sebastian; van de Ven, Glenn; Seth, Anil C.; Voggel, Karina T.; Georgiev, Iskren Y.; Leaman, Ryan; Bianchini, Paolo; Böker, Torsten; Mieske, SteffenWe present comprehensive multicomponent dynamical models of M54 (NGC 6715), the nuclear star cluster of the Sagittarius (Sgr) dwarf galaxy, which is undergoing a tidal disruption in the Milky Way halo. Previous papers in this series used a large MUSE mosaic data set to identify multiple stellar populations in the system and study their kinematic differences. Here, we use Jeans-based dynamical models that fit the population properties (mean age and metallicity), spatial distributions, and kinematics simultaneously. They provide a solid physical explanation for our previous findings. Population-dynamical models deliver a comprehensive view of the whole system, and allow us to disentangle the different stellar populations. We explore their dynamical interplay and confirm our previous findings about the build-up of Sgr’s nuclear cluster via contributions from globular cluster stars, Sgr inner field stars, and in situ star formation. We explore various parameterizations of the gravitational potential and show the importance of a radially varying mass-to-light ratio for the proper treatment of the mass profile. We find a total dynamical mass within M54's tidal radius (∼75 pc) of 1.60 ± 0.07 × 106 M ⊙ in excellent agreement with N-body simulations. Metal-poor globular cluster stars contribute about 65% of the total mass or 1.04 ± 0.05 × 106 M ⊙. Metal-rich stars can be further divided into young and intermediate-age populations, which contribute 0.32 ± 0.02 × 106 M ⊙ (20%) and 0.24 ± 0.02 × 106 M ⊙ (15%), respectively. Our population-dynamical models successfully distinguish the different stellar populations in Sgr’s nucleus because of their different spatial distributions, ages, metallicities, and kinematic features.
- ItemOn the Use of Field RR Lyrae as Galactic Probes. V. Optical and Radial Velocity Curve Templates(London : Institute of Physics Publ., 2021) Braga, V.F.; Crestani, J.; Fabrizio, M.; Bono, G.; Sneden, C.; Preston, G. W.; Storm, J.; Kamann, S.; Latour, M.; Lala, H.; Lemasle, B.; Prudil, Z.; Altavilla, G.; Chaboyer, B.; Dall’Ora, M.; Ferraro, I.; Gilligan, C. K.; Fiorentino, G.; Iannicola, G.; Inno, L.; Kwak, S.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martínez-Vázquez, C.E.; Monelli, M.; Mullen, J.P.; Matsunaga, N.; Neeley, J.; Stetson, P. B.; Valenti, E.; Zoccali, M.We collected the largest spectroscopic catalog of RR Lyrae (RRLs) including ≈20,000 high-, medium-, and low-resolution spectra for ≈10,000 RRLs. We provide the analytical forms of radial velocity curve (RVC) templates. These were built using 36 RRLs (31 fundamental - split into three period bins - and five first-overtone pulsators) with well-sampled RVCs based on three groups of metallic lines (Fe, Mg, Na) and four Balmer lines (H α , H β , H γ , H δ ). We tackled the long-standing problem of the reference epoch to anchor light-curve and RVC templates. For the V-band, we found that the residuals of the templates anchored to the phase of the mean magnitude along the rising branch are ∼35% to ∼45% smaller than those anchored to the phase of maximum light. For the RVC, we used two independent reference epochs for metallic and Balmer lines and we verified that the residuals of the RVC templates anchored to the phase of mean RV are from 30% (metallic lines) up to 45% (Balmer lines) smaller than those anchored to the phase of minimum RV. We validated our RVC templates by using both the single-point and the three phase point approaches. We found that barycentric velocities based on our RVC templates are two to three times more accurate than those available in the literature. We applied the current RVC templates to Balmer lines RVs of RRLs in the globular NGC 3201 collected with MUSE at VLT. We found the cluster barycentric RV of V γ = 496.89 ± 8.37(error) ± 3.43 (standard deviation) km s-1, which agrees well with literature estimates.