Understanding the central kinematics of globular clusters with simulated integrated-light IFU observations

Abstract

The detection of intermediate mass black holes in the centres of globular clusters is highly controversial, as complementary observational methods often deliver significantly different results. In order to understand these discrepancies, we develop a procedure to simulate integral field unit (IFU) observations of globular clusters: Simulating IFU Star Cluster Observations (SISCO). The input of our software are realistic dynamical models of globular clusters that are then converted in a spectral data cube. We apply SISCO to Monte Carlo cluster simulations from Downing et al. (2010), with a realistic number of stars and concentrations. Using independent realisations of a given simulation we are able to quantify the stochasticity intrinsic to the problem of observing a partially resolved stellar population with integrated-light spectroscopy. We show that the luminosity-weighted IFU observations can be strongly biased by the presence of a few bright stars that introduce a scatter in the velocity dispersion measurements up to $\simeq$40% around the expected value, preventing any sound assessment of the central kinematic and a sensible interpretation of the presence/absence of an intermediate mass black hole. Moreover, we illustrate that, in our mock IFU observations, the average kinematic tracer has a mass of $\simeq$0.75 solar masses, only slightly lower than the mass of the typical stars examined in studies of resolved line-of-sight velocities of giant stars. Finally, in order to recover unbiased kinematic measurements we test different masking techniques that allow us to remove the spaxels dominated by bright stars, bringing the scatter down to a level of only a few percent. The application of SISCO will allow to investigate state-of-the-art simulations as realistic observations.

13 pages, 9 figures, 1 table. Accepted for publication in MNRAS

References in corpus (9)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• GALEV evolutionary synthesis models - I. Code, input physics and web-interface
• Hubble Space Telescope Proper Motion (HSTPROMO) Catalogs of Galactic Globular Clusters. I. Sample Selection, Data Reduction and NGC 7078 Results
• Hubble Space Telescope proper motion (HSTPROMO) catalogs of Galactic globular clusters. II. Kinematic profiles and maps
• Central rotations of Milky Way Globular Clusters
• The Gaia-ESO Survey: Kinematics of seven Galactic globular clusters
• Radio observations of NGC 2808 and other globular clusters: constraints on intermediate mass black holes
• A study of rotating globular clusters - the case of the old, metal-poor globular cluster NGC 4372
• The central dynamics of M3, M13, and M92: Stringent limits on the masses of intermediate-mass black holes

Cited by in corpus (16)

• MOCCA Code for Star Cluster Simulations - IV. A new Scenario for Intermediate Mass Black Hole Formation in Globular Clusters
• Unification of the Fundamental Plane and Super-Massive Black Holes Masses
• Intermediate mass black holes from stellar mergers in young star clusters
• Triaxial orbit-based modelling of the Milky Way Nuclear Star Cluster
• Radial anisotropy in omega Cen limiting the room for an intermediate-mass black hole
• On the black hole content and initial mass function of 47 Tuc
• A re-evaluation of the central velocity-dispersion profile in NGC 6388
• Dynamical analysis of the dark matter and central black hole mass in the dwarf spheroidal Leo I
• MOCCA-SURVEY Database I: Is NGC 6535 a Dark Star Cluster Harboring an IMBH?
• Dynamical modelling of globular clusters: challenges for the robust determination of IMBH candidates
• SimSpin -- Constructing mock IFS kinematic data cubes
• Prospects for detection of intermediate-mass black holes in globular clusters using integrated-light spectroscopy
• Central kinematics of the Galactic globular cluster M80
• COCOA Code for Creating Mock Observations of Star Cluster Models
• The Lost Dwarfs of Centaurus A and the Formation of its Dark Globular Clusters
• Predicting Images for the Dynamics Of stellar Clusters (π-DOC): a deep learning framework to predict mass, distance and age of globular clusters