scholarly journals Hunting for intermediate-mass black holes in globular clusters: an astrometric study of NGC 6441

2021 ◽  
Vol 503 (1) ◽  
pp. 1490-1506
Author(s):  
Maximilian Häberle ◽  
Mattia Libralato ◽  
Andrea Bellini ◽  
Laura L Watkins ◽  
Jörg-Uwe Pott ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Velocity Dispersion ◽  
Angular Resolution ◽  
Hubble Space Telescope ◽  
High Mass ◽  
High Angular Resolution ◽  
Stellar Kinematics ◽  
Intermediate Mass ◽  
The Core ◽  
Large Telescopes

ABSTRACT We present an astrometric study of the proper motions (PMs) in the core of the globular cluster NGC 6441. The core of this cluster has a high density and observations with current instrumentation are very challenging. We combine ground-based, high-angular-resolution NACO@VLT images with Hubble Space Telescope ACS/HRC data and measure PMs with a temporal baseline of 15 yr for about 1400 stars in the centremost 15 arcsec of the cluster. We reach a PM precision of ∼30 µas yr−1 for bright, well-measured stars. Our results for the velocity dispersion are in good agreement with other studies and extend already existing analyses of the stellar kinematics of NGC 6441 to its centremost region never probed before. In the innermost arcsecond of the cluster, we measure a velocity dispersion of (19.1 ± 2.0) km s−1 for evolved stars. Because of its high mass, NGC 6441 is a promising candidate for harbouring an intermediate-mass black hole (IMBH). We combine our measurements with additional data from the literature and compute dynamical models of the cluster. We find an upper limit of $M_{\rm IMBH} \lt 1.32 \times 10^4\, \textrm{M}_\odot$ but we can neither confirm nor rule out its presence. We also refine the dynamical distance of the cluster to $12.74^{+0.16}_{-0.15}$ kpc. Although the hunt for an IMBH in NGC 6441 is not yet concluded, our results show how future observations with extremely large telescopes will benefit from the long temporal baseline offered by existing high-angular-resolution data.

scholarly journals AGBs, Post-AGBs and the Shaping of Planetary Nebulae

Galaxies ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 99 ◽  
Author(s):  
Eric Lagadec
Keyword(s):  
Angular Resolution ◽  
Hubble Space Telescope ◽  
Planetary Nebulae ◽  
High Angular Resolution ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Shaping Process ◽  
Huge Variety ◽  
Isotropic Radiation

During the last decades, observations, mostly with the Hubble Space Telescope, have revealed that round Planetary Nebulae were the exception rather than rule. A huge variety of features are observed, such as jets, discs, tori, showing that the ejection of material is not due to isotropic radiation pressure on a spherical shell and that more physics is involved. This shaping process certainly occur early in the evolution of these low and intermediate mass stars and must leave imprints in the evolutionary stages prior the PN phase. Thanks to news instruments on the most advanced telescopes (e.g., the VLTI, SPHERE/VLT and ALMA), high angular resolution observations are revolutionising our view of the ejection of gas and dust during the AGB and post-AGB phases. In this review I will present the newest results concerning the mass loss from AGB stars, post-AGB stars and related objects.

scholarly journals Simulations of HST Observations of Globular Clusters

1988 ◽  
Vol 126 ◽  
pp. 455-464
Author(s):  
John N. Bahcall ◽  
Donald P. Schneider
Keyword(s):  
Globular Clusters ◽  
Angular Resolution ◽  
Hubble Space Telescope ◽  
High Angular Resolution ◽  
Space Telescope ◽  
Science Institute ◽  
Galactic Globular Clusters ◽  
Space Telescope Science Institute

The high angular resolution of the Hubble Space Telescope will provide opportunities for many fundamental observations of globular clusters, most of which have been extensively discussed in the literature. We have therefore chosen to devote our time (and pages) to a presentation of what HST observations may reveal about some aspects of galactic globular clusters. To avoid infringing upon programs that others may propose, we have limited ourselves to simulations of observations that are part of our Guaranteed Time Observations. [The complete catalog of GTO observations has published by the Space Telescope Science Institute and is available upon request.]

scholarly journals New insights into star cluster evolution towards energy equipartition

2021 ◽  
Vol 504 (1) ◽  
pp. L12-L16
Author(s):  
Václav Pavlík ◽  
Enrico Vesperini
Keyword(s):  
Radial Velocity ◽  
Globular Clusters ◽  
Velocity Dispersion ◽  
Tangential Velocity ◽  
Star Cluster ◽  
High Mass ◽  
Stellar Kinematics ◽  
Low Mass Stars ◽  
Velocity Anisotropy ◽  
Energy Equipartition

ABSTRACT We present the results of a study aimed at exploring the evolution towards energy equipartition in star cluster models with different initial degrees of anisotropy in the velocity distribution. Our study reveals a number of novel aspects of the cluster dynamics and shows that the rate of evolution towards energy equipartition (i) depends on the initial degree of radial velocity anisotropy – it is more rapid for more radially anisotropic systems; and (ii) differs for the radial and the tangential components of the velocity dispersion. (iii) The outermost regions of the initially isotropic system evolve towards a state of ‘inverted’ energy equipartition in which high-mass stars have a larger velocity dispersion than low-mass stars – this inversion originates from the mass dependence of the tangential velocity dispersion whereas the radial velocity dispersion shows no anomaly. Our results add new fundamental elements to the theoretical framework needed to interpret the wealth of recent and upcoming observational studies of stellar kinematics in globular clusters, and shed further light on the link between the clusters’ internal kinematics, their formation, and evolutionary history.

scholarly journals Kinematics of the outskirts of S0 galaxies from PNe and GCs

2016 ◽  
Vol 11 (S321) ◽  
pp. 290-290
Author(s):  
A. Cortesi ◽  
C. Mendes de Oliveira
Keyword(s):  
Galaxy Formation ◽  
Globular Clusters ◽  
Velocity Dispersion ◽  
Spiral Galaxies ◽  
Formation Mechanisms ◽  
Stellar Kinematics ◽  
Lenticular Galaxies ◽  
Star Forming ◽  
Flat Rotation Curves ◽  
S0 Galaxies

AbstractThe stellar kinematics of the discs of S0 galaxies (as obtained using planetary nebulae, PNe, and integrated stellar light data) is comparable to that of spiral galaxies, with similar flat rotation curves and falling velocity dispersion profiles, but they present a larger amount of random motions. The only other tracer available to probe the kinematics of individual early-type galaxies are globular clusters (GCs). GCs’ formation is intimately connected to a galaxy major star forming event(s) and GCs are, therefore, good proofs of galaxy formation histories. We directly compare a sample of PNe, GCs, and stellar velocities out to 4 effective radii, in the S0 galaxies NGC 2768 and NGC 1023. In particular, we test a new method for studying GC properties and we find that these two lenticular galaxies are consistent with being formed through different formation mechanisms.

scholarly journals Constraining VLBI−optical offsets in high redshift galaxies using strong gravitational lensing

2020 ◽  
Vol 494 (2) ◽  
pp. 2312-2326 ◽  
Author(s):  
Cristiana Spingola ◽  
Anna Barnacka
Keyword(s):  
Gravitational Lensing ◽  
Angular Resolution ◽  
Hubble Space Telescope ◽  
High Redshift ◽  
Monte Carlo Sampling ◽  
High Angular Resolution ◽  
Radio Emissions ◽  
High Redshift Galaxies ◽  
Long Baseline ◽  
Redshift Galaxies

ABSTRACT We present a multiwavelength analysis of two highly magnified strong gravitationally lensed galaxies, CLASS B0712+472 and CLASS B1608+656, at redshifts 1.34 and 1.394, respectively, using new VLBI (very long baseline interferometry) and archival Hubble Space Telescope observations. We reconstruct the positions of the radio and optical emissions with their uncertainties using Monte Carlo sampling. We find that in CLASS B0712+472 the optical and radio emissions are co-spatial within 2 ± 5 mas (17 ± 42 pc at redshift of 1.34). But, in CLASS B1608+656, we reconstruct an optical–radio offset of 25 ± 16 mas (214 ± 137 pc at redshift of 1.394), among the smallest offsets measured for an AGN (active galactic nucleus) at such high redshift. The spectral features indicate that CLASS B1608+656 is a post-merger galaxy, which, in combination with the optical–VLBI offset reported here, makes CLASS B1608+656 a promising candidate for a high- z offset–AGN. Furthermore, the milliarcsecond angular resolution of the VLBI observations combined with the precise lens models allow us to spatially locate the radio emission at 0.05 mas precision (0.4 pc) in CLASS B0712+472, and 0.009 mas precision (0.08 pc) in CLASS B1608+656. The search for optical–radio offsets in high redshift galaxies will be eased by the upcoming synoptic all-sky surveys, including Extremely Large Telescope and Square Kilometre Array, which are expected to find ∼105 strongly lensed galaxies, opening an era of large strong lensing samples observed at high angular resolution.

scholarly journals No evidence for intermediate-mass black holes in the globular clusters ω Cen and NGC 6624

2019 ◽  
Vol 488 (4) ◽  
pp. 5340-5351 ◽  
Author(s):  
H Baumgardt ◽  
C He ◽  
S M Sweet ◽  
M Drinkwater ◽  
A Sollima ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Globular Clusters ◽  
Surface Brightness ◽  
Velocity Dispersion ◽  
Stellar Mass ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Measured Velocity ◽  
Large Grid

ABSTRACT We compare the results of a large grid of N-body simulations with the surface brightness and velocity dispersion profiles of the globular clusters ω Cen and NGC 6624. Our models include clusters with varying stellar-mass black hole retention fractions and varying masses of a central intermediate-mass black hole (IMBH). We find that an $\sim 45\, 000$ M⊙ IMBH, whose presence has been suggested based on the measured velocity dispersion profile of ω Cen, predicts the existence of about 20 fast-moving, m > 0.5 M⊙, main-sequence stars with a (1D) velocity v > 60 km s−1 in the central 20 arcsec of ω Cen. However, no such star is present in the HST/ACS proper motion catalogue of Bellini et al. (2017), strongly ruling out the presence of a massive IMBH in the core of ω Cen. Instead, we find that all available data can be fitted by a model that contains 4.6 per cent of the mass of ω Cen in a centrally concentrated cluster of stellar-mass black holes. We show that this mass fraction in stellar-mass BHs is compatible with the predictions of stellar evolution models of massive stars. We also compare our grid of N-body simulations with NGC 6624, a cluster recently claimed to harbour a 20 000 M⊙ black hole based on timing observations of millisecond pulsars. However, we find that models with MIMBH > 1000 M⊙ IMBHs are incompatible with the observed velocity dispersion and surface brightness profile of NGC 6624, ruling out the presence of a massive IMBH in this cluster. Models without an IMBH provide again an excellent fit to NGC 6624.

scholarly journals HIGH-ANGULAR-RESOLUTION OBSERVATIONS AT 7 MM OF THE CORE OF THE QUADRUPOLAR HH 111/121 OUTFLOW

2008 ◽  
Vol 136 (5) ◽  
pp. 1852-1856 ◽  
Author(s):  
Luis F. Rodríguez ◽  
José M. Torrelles ◽  
Guillem Anglada ◽  
Bo Reipurth
Keyword(s):  
Angular Resolution ◽  
High Angular Resolution ◽  
The Core

scholarly journals High-angular resolution observations towards OMC-2 FIR 4: Dissecting an intermediate-mass protocluster

2013 ◽  
Vol 556 ◽  
pp. A62 ◽  
Author(s):  
A. López-Sepulcre ◽  
V. Taquet ◽  
Á. Sánchez-Monge ◽  
C. Ceccarelli ◽  
C. Dominik ◽  
...  
Keyword(s):  
Angular Resolution ◽  
High Angular Resolution ◽  
Intermediate Mass

scholarly journals On the Age of Galactic Bulge CSPNe: Too Young and Complicated?

Galaxies ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 51
Author(s):  
Foteini Lykou ◽  
Albert Zijlstra ◽  
Quentin A. Parker
Keyword(s):  
Angular Resolution ◽  
Hubble Space Telescope ◽  
Planetary Nebulae ◽  
Small Sample ◽  
Mixed Population ◽  
High Angular Resolution ◽  
Galactic Bulge ◽  
Current Analysis ◽  
Stellar Masses ◽  
Central Stars

We present preliminary results of our study of a small sample of planetary nebulae in the Galactic Bulge for which high-angular resolution Hubble Space Telescope imaging is available. From this and from archival spectroscopy, we were able to calculate temperatures and luminosities for their central stars. These were then correlated to up-to-date evolutionary tracks found in the literature to help us estimate stellar masses and therefore ages for the central stars. Our current analysis indicates that our sample appears to represent a somewhat mixed population of planetary nebulae central stars, while at least one of the nebulae might have been formed by a more massive progenitor (i.e., M ZAMS ∼ 4 M ⊙ ).

scholarly journals Fragmentation and dynamics in Massive Dense Cores in Cygnus-X

2010 ◽  
Vol 6 (S270) ◽  
pp. 53-56 ◽  
Author(s):  
T. Csengeri ◽  
S. Bontemps ◽  
N. Schneider ◽  
F. Motte
Keyword(s):  
Angular Resolution ◽  
High Density ◽  
High Mass ◽  
High Angular Resolution ◽  
Low Mass Stars ◽  
Dense Cores ◽  
Evolutionary Scenario ◽  
Low Mass ◽  
Molecular Tracers ◽  
Resolution Study

AbstractA systematic, high angular-resolution study of IR-quiet Massive Dense Cores (MDCs) of Cygnus-X in continuum and high-density molecular tracers is presented. The results are compared with the quasi-static and the dynamical evolutionary scenario. We find that the fragmentation properties are not compatible with the quasi-static, monolithic collapse scenario, nor are they entirely compatible with the formation of a cluster of mostly low-mass stars. The kinematics of MDCs shows individual velocity components appearing as coherent flows, which indicate important dynamical processes at the scale of the mass reservoir around high-mass protostars.

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