arXiv subjects

A. Leveque

Publications and source records attributed to A. Leveque.

5 recordsLinked to original sources

arXiv2023

MOCCA-Survey Database: Extra Galactic Globular Clusters. III. The population of black holes in Milky Way and Andromeda-like galaxies

In this work, we investigate the black hole (BH) population of globular clusters (GCs) in Milky Way- (MW) and Andromeda- (M31) like galaxies. We combine the population synthesis code MASinGa and the MOCCA-Survey Database I to infer the properties of GCs harbouring a BH subsystem (BHS), an IMBH, or neither of those. We find that the typical number of GCs with a BHS, an IMBH, or none become comparable in the galactic outskirts, whilst the inner galactic regions are dominated by GCs without a significant dark component. Our models suggest that GCs harbouring a BHS are slightly heavier and with larger half-mass radii compared to the overall population. We retrieve the properties of binary BHs (BBHs) that have either merged in the last 3 Gyr or survived in their parent cluster until present-day. We find that around 80\% of the merging BBHs form due to dynamical interactions while the remaining originate from evolution of primordial binaries. We infer a merger rate for BBHs in the local Universe of $1.0-23\,\,\rm{yr^{-1}\,Gpc^{-3}}$, depending on the adopted assumptions. We find around 100-240 BBHs survive until present-day and are mostly concentrated in the inner few kpc of the galaxy. We estimate also the number of BHs transported into the galactic nucleus by infalling star clusters, finding around 1,000-3,000 BHs and 100-200 BBHs are transported over a time span of 12 Gyr. This enables us to constrains the total amount of BHs and BBHs binaries lurking in nuclear star cluster, i.e. $N_{BHs}=(1.4-2.2)\times10^4$ and $N_{BBHs}=700-1,100$.

astro-ph.GA↗

arXiv2022

MOCCA-Survey Database: Extra Galactic Globular Clusters. II. Milky Way and Andromeda

A comprehensive study of the co-evolution of globular cluster systems (GCS) in galaxies requires the ability to model both the large scale dynamics (0.01 - 10 kpc) regulating their orbital evolution, and the small scale dynamics (sub-pc - AU) regulating the internal dynamics of each globular cluster (GC). In this work we present a novel method that combine semi-analytic models of GCS with fully self-consistent Monte Carlo models to simultaneously evolve large GCSs. We use the population synthesis code MASinGa and the MOCCA-Survey Database I to create synthetic GC populations aimed at representing the observed features of GCs in the Milky Way (MW) and Andromeda (M31). Our procedure enables us to recover the spatial and mass distribution of GCs in such galaxies, and to constrain the amount of mass that GCs left either in the halo as dispersed debris, or in the galactic centre, where they can contribute to the formation of a nuclear star cluster (NSC) and can bring stellar and possibly intermediate mass black holes there. The final masses reported by our simulations are of a few order of magnitudes smaller than the observed values. These differences show that mass build-up of a NSC and central BHs in galaxies like MW and M31 cannot be solely explained by the infalling GC scenario. This build-up is likely to depend on the interplay between interactions and mergers of infalling GCs and gas. The latter can contribute to both in-situ star formation in the NSC and growth of the central BH.

astro-ph.GA↗

arXiv2022

A Monte Carlo study of early gas expulsion and evolution of star clusters: new simulations with the MOCCA code in the AMUSE framework

We introduce a new prescription for the evolution of globular clusters (GCs) during the initial embedded gas phase into a Monte Carlo method. With a simplified version of the Monte Carlo MOCCA code embedded in the AMUSE framework, we study the survival of GCs after the removal of primordial gas. We first test our code and show that our results for the evolution of mass and Lagrangian radii are in good agreement with those obtained with N-body simulations. The Monte Carlo code enables a more rapid exploration of the evolution of systems with a larger number of stars than N-body simulations. We have carried out a new survey of simulations to explore the evolution of globular clusters with up to $N = 500000$ stars for a range of different star formation efficiencies and half-mass radii. Our study shows the range of initial conditions leading to the clusters' dissolution and those for which the clusters can survive this early evolutionary phase.

astro-ph.GA↗

arXiv2021

Preparing the next gravitational million-body simulations: Evolution of single and binary stars in Nbody6++GPU, MOCCA and McLuster

We present the implementation of updated stellar evolution recipes in the codes \texttt{Nbody6++GPU, MOCCA} and \texttt{McLuster}. We test them through numerical simulations of star clusters containing $1.1\times 10^5$ stars (with $2.0\times 10^4$ in primordial hard binaries) performing high-resolution direct $N$-body (\texttt{Nbody6++GPU}) and Monte-Carlo (\texttt{MOCCA}) simulations to an age of 10~Gyr. We compare models implementing either delayed or core-collapse supernovae mechanisms, a different mass ratio distribution for binaries, and white dwarf natal kicks enabled/disabled. Compared to \texttt{Nbody6++GPU}, the \texttt{MOCCA} models appear to be denser, with a larger scatter in the remnant masses, and a lower binary fraction on average. The \texttt{MOCCA} models produce more black holes (BHs) and helium white dwarfs (WDs), whilst \texttt{Nbody6++GPU} models are characterised by a much larger amount of WD-WD binaries. The remnant kick velocity and escape speed distributions are similar for the BHs and neutron stars (NSs), and some NSs formed via electron-capture supernovae, accretion-induced collapse or merger-induced collapse escape the cluster in all simulations. The escape speed distributions for the WDs, on the other hand, are very dissimilar. We categorise the stellar evolution recipes available in \texttt{Nbody6++GPU}, \texttt{MOCCA} and \texttt{Mcluster} into four levels: the one implemented in previous \texttt{Nbody6++GPU} and \texttt{MOCCA} versions (\texttt{level A}), state-of-the-art prescriptions (\texttt{level B}), some in a testing phase (\texttt{level C}), and those that will be added in future versions of our codes.

astro-ph.GA↗

arXiv2015

NectarCAM : a camera for the medium size telescopes of the Cherenkov Telescope Array

NectarCAM is a camera proposed for the medium-sized telescopes of the Cherenkov Telescope Array (CTA) covering the central energy range of ~100 GeV to ~30 TeV. It has a modular design and is based on the NECTAr chip, at the heart of which is a GHz sampling Switched Capacitor Array and a 12-bit Analog to Digital converter. The camera will be equipped with 265 7-photomultiplier modules, covering a field of view of 8 degrees. Each module includes the photomultiplier bases, high voltage supply, pre-amplifier, trigger, readout and Ethernet transceiver. The recorded events last between a few nanoseconds and tens of nanoseconds. The camera trigger will be flexible so as to minimize the read-out dead-time of the NECTAr chips. NectarCAM is designed to sustain a data rate of more than 4 kHz with less than 5\% dead time. The camera concept, the design and tests of the various subcomponents and results of thermal and electrical prototypes are presented. The design includes the mechanical structure, cooling of the electronics, read-out, clock distribution, slow control, data-acquisition, triggering, monitoring and services.

astro-ph.IM↗