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

Bianchini, P.; Norris, Mark A.; Ven, Glenn van de; Schinnerer, E.

doi:10.1093/mnras/stv1651

Cited by 24 publications

(23 citation statements)

References 40 publications

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“…However, the simulations of the innermost bin result in a very large scatter and an uncertainty of more than 20%. Similar results have also been reported by Bianchini et al (2015). The highest values for σ also show a slight trend toward lower values, but are still consistent with the input velocity dispersion when taking the large uncertainties into account.…”

Section: Discussion Of the Biassupporting

confidence: 90%

Re-evaluation of the central velocity-dispersion profile in NGC 6388

Lützgendorf

Gebhardt

Baumgardt

et al. 2015

A&A

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Context. The globular cluster NGC 6388 is one of the most massive clusters in our Milky Way and has been the subject of many studies. Recently, two independent groups found very different results when measuring its central velocity-dispersion profile with different methods. While we found a rising profile and a high central velocity dispersion (23.3 km s −1 ), measurements obtained by Lanzoni et al. (2013, ApJ, 769, 107) showed a value lower by 40%. The value of the central velocity dispersion has a serious effect on the mass and possible presence of an intermediate-mass black hole at the center of NGC 6388. Aims. The goal of this paper is to quantify the biases arising from measuring velocity dispersions from individual extracted stellar velocities versus the line broadening measurements of the integrated light using new tools to simulate realistic observations made with integral field units (IFU). Methods. We used a photometric catalog of NGC 6388 to extract the positions and magnitudes from the brightest stars in the central three arcseconds of NGC 6388 and created a simulated SINFONI and ARGUS dataset. The IFU data cube was constructed with different observing conditions (i.e., Strehl ratios and seeing) reproducing the conditions reported for the original observations as closely as possible. In addition, we produced an N-body realization of a ∼10 6 M stellar cluster with the same photometric properties as NGC 6388 to account for unresolved stars. Results. We find that the individual radial velocities, that is, the measurements from the simulated SINFONI data, are systematically biased towards lower velocity dispersions. The reason is that the velocities become biased toward the mean cluster velocity as a result of the wings in the point spread function of adaptive optics (AO) corrected data sets. This study shows that even with AO supported observations, individual radial velocities in crowded fields do not reproduce the true velocity distribution. The ARGUS observations do not show this kind of bias, but they were found to have larger uncertainties than previously obtained. We find a bias toward higher velocity dispersions in the ARGUS pointing when fixing the extreme velocities of the three brightest stars, but these variations are within the determined uncertainties. We reran Jeans models and fit them to the kinematic profile with the new uncertainties. This yielded a black-hole mass of M • = (2.8 ± 0.4) × 10 4 M and M/L ratio M/L = (1.6 ± 0.1) M /L , consistent with our previous results.

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Section: Discussion Of the Biassupporting

confidence: 90%

Re-evaluation of the central velocity-dispersion profile in NGC 6388

Lützgendorf

Gebhardt

Baumgardt

et al. 2015

A&A

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“…Observational limitations and biases (e.g. van den Bosch & de Zeeuw 2010;Bianchini et al 2015) have prevented the confirmation of central intermediate-mass BHs (IMBHs) in Local Group GCs (e.g. Sun et al 2013;Kamann et al 2014;Lützgendorf et al 2015;Cseh et al 2015;Wrobel et al 2015).…”

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confidence: 99%

The Lost Dwarfs of Centaurus a and the Formation of Its Dark Globular Clusters

Bovill

Puzia

Ricotti

et al. 2016

ApJ

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We present theoretical constraints for the formation of the newly discovered dark star clusters (DSCs) with high mass-to-light (M/L) ratios, from Taylor et al (2015). These compact stellar systems photometrically resemble globular clusters (GCs) but have dynamical M/L ratios of ∼ 10−100, closer to the expectations for dwarf galaxies. The baryonic properties of the dark star clusters (DSCs) suggest their host dark matter halos likely virialized at high redshift with M > 10 8 M . We use a new set of high-resolution N-body simulations of Centaurus A to determine if there is a set of z = 0 subhalos whose properties are in line with these observations. While we find such a set of subhalos, when we extrapolate the dark matter density profiles into the inner 20 pc, no dark matter halo associated with Centaurus A in our simulations, at any redshift, can replicate the extremely high central mass densities of the DSCs. Among the most likely options for explaining 10 5 −10 7 M within 10 pc diameter subhalos is the presence of a central massive black hole. We, therefore, propose that the DSCs are remnant cusps of stellar systems surrounding the central black holes of dwarf galaxies which have been almost completely destroyed by interactions with Centaurus A.

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“…cocoa has been used to check whether such dark star clusters are observed in the Galaxy. In Askar et al (2017a) a comparison for the observed photometric properties of a simulation model was carried out using cocoa which together with mock kinematic observations from sisco (Bianchini et al 2015) helped to identify NGC 6535 as a possible candidate for harbouring an IMBH.…”

Section: Discussionmentioning

confidence: 99%

COCOA Code for Creating Mock Observations of Star Cluster Models

Askar

Giersz

Pych

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We introduce and present results from the cocoa (Cluster simulatiOn Comparison with ObservAtions) code that has been developed to create idealized mock photometric observations using results from numerical simulations of star cluster evolution. cocoa is able to present the output of realistic numerical simulations of star clusters carried out using Monte Carlo or N -body codes in a way that is useful for direct comparison with photometric observations. In this paper, we describe the cocoa code and demonstrate its different applications by utilizing globular cluster (GC) models simulated with the mocca (MOnte Carlo Cluster simulAtor) code. cocoa is used to synthetically observe these different GC models with optical telescopes, perform PSF photometry and subsequently produce observed colour magnitude diagrams. We also use cocoa to compare the results from synthetic observations of a cluster model that has the same age and metallicity as the Galactic GC NGC 2808 with observations of the same cluster carried out with a 2.2 meter optical telescope. We find that cocoa can effectively simulate realistic observations and recover photometric data. cocoa has numerous scientific applications that maybe be helpful for both theoreticians and observers that work on star clusters. Plans for further improving and developing the code are also discussed in this paper.

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

Cited by 24 publications

References 40 publications

Re-evaluation of the central velocity-dispersion profile in NGC 6388

Re-evaluation of the central velocity-dispersion profile in NGC 6388

The Lost Dwarfs of Centaurus a and the Formation of Its Dark Globular Clusters

COCOA Code for Creating Mock Observations of Star Cluster Models

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