arXiv subjects

T. Panamarev

Publications and source records attributed to T. Panamarev.

4 recordsLinked to original sources

arXiv2026

The contribution to Galactic Centre {\gamma}-ray excess from cluster-born millisecond pulsars. Constraints from direct N-body simulations

The Galactic Centre {\gamma}-ray excess (GCE), observed by Fermi-LAT around Sgr A*, exceeds expectations from standard cosmic-ray models and is commonly attributed either to dark matter annihilation or to unresolved millisecond pulsars (MSPs). We revisit the MSP scenario within a fully dynamical framework by tracking neutron stars (NSs) formed in globular clusters (GCs) and deposited into the central kiloparsec. Using high-resolution direct N-body simulations of GCs evolving in a time-dependent Milky Way potential, we model both present-day clusters and an early population of disrupted systems. From the simulated NS distributions, we infer the MSP population via an empirically calibrated MSP-to-NS ratio and construct mock {\gamma}-ray flux profiles assuming representative pulsar luminosities. MSPs associated with surviving clusters already produce a substantial {\gamma}-ray contribution, while disrupted clusters enhance both the amplitude and central concentration of the signal. Under reasonable assumptions, the combined MSP population reproduces the observed GCE properties, favouring an astrophysical origin over dark matter interpretations.

astro-ph.HE↗

arXiv2026

How our proto-nuclear star cluster formed and grew due to early globular cluster disruption. I. Case of low masses

We investigate the accretion of globular cluster stars on early cosmological timescales through detailed N-body simulations of theoretical GC models to assess the role of this mechanism in Milky Way-like galaxies. For the dynamical modelling, we used the updated parallel N-body code phi-GPU, including stellar evolution. We prepared three sets of GC models with different half-mass radii (r_hm), each consisting of 50 full N-body GC models, and integrated these models in an external, time-variable MW-like potential taken from the cosmological database IllustrisTNG-100. The simulations cover the time interval from -10 Gyr to -5 Gyr, enabling us to assess the rate of early stellar accretion onto the proto-NSC. We find that GC models with average orbital eccentricities of 0.4-0.5 and orbits oriented perpendicular to the galactic disc contribute most significantly to the mass of the proto-NSC formation. Accretion is especially efficient in the first billion years and in compact GC models with r_hm = 1 pc. In all sets, the dominant accreted stellar population consists of low-mass stars (~0.33 Msun). However, the accreted mass alone is insufficient to fully account for the current NSC mass. Based on our extended set of numerical simulations, we obtained an average lower limit of mass contribution (~6 percent) to the NSC from investigated GCs. The fraction of mass contribution from individual disrupted GCs can significantly vary from 0.1 percent up to 90 percent. Generally, we conclude that the GC stellar accretion channel alone might not be sufficient to ensure the present-day MW galaxy NSC mass budget.

astro-ph.GA↗

arXiv2024

Dynamical evolution of Milky Way globular clusters on the cosmological timescale I. Mass loss and interaction with the nuclear star cluster

Context. Based on the Gaia DR3, we reconstructed the orbital evolution of the known Milky Way globular clusters and found that six objects, NGC 6681, NGC 6981, Palomar 6, NGC 6642, HP 1, and NGC 1904, very likely interact closely with the nuclear star cluster. Aims. We study the dynamical evolution of selected Milky Way globular clusters and their interactions with the Galactic centre over cosmological timescales. We examine the global dynamical mass loss of these globular cluster systems, their close interactions with the Galactic centre, and the potential capture of stars by the Milky Way nuclear star cluster. Methods. For the dynamical modelling of the clusters, we used the parallel N-body code phi-GPU, which allows star-by-star simulations of the systems. Our current code also enabled us to follow the stellar evolution of individual particles, including the formation of high-mass remnants. The modelling was carried out in a Milky Way-like, time-variable potential (with a dynamically changing mass and scale length), obtained from the IllustrisTNG-100 database, with a full integration time of eight billion years. Results. Based on extensive numerical modelling and analysis, we estimated the mass loss and the global and inner structures of the selected six clusters. Over an evolution of eight billion years, the clusters lost 80% of their initial mass. We analysed the phase-space evolution of the individual unbound stars NGC 6681, NGC 6642, HP 1, and NGC 1904. We found that only NGC 6642 could potentially have been a source for populating the Milky Way nuclear star cluster in the past.

astro-ph.GA↗

arXiv2021

The bound mass of Dehnen models with centrally peaked star formation efficiency

Understanding the formation of star clusters with low star-formation efficiency (SFE) is very important to know about the star-formation history. In N-body models of star cluster evolution after gas expulsion, the Plummer model with outer power law density profile has been used massively. We study the impact of the density profile slopes on the survivability of the low-SFE star clusters after instantaneous gas expulsion. We compare cases when stellar cluster has Plummer profile and Dehnen profiles with cusp of different slopes at the time of formation. We determine the corresponding density profile of the residual gas for a given global SFE, assuming that our model clusters formed with a constant efficiency per free-fall time and hence have shallower density profile of gas than that of stars. We perform direct $N$-body simulations of evolution of clusters initially in virial equilibrium within gas potential after gas removal. We find that the violent relaxation lasts no longer than 20~Myr independently of the density profile power law slopes. Dehnen model clusters survive after violent relaxation with significantly lower SFEs when the global SFE measured within the Jacobi radius or within a half-mass radius. Dehnen $γ=0$ model clusters show similar final bound fraction with the Plummer model clusters if global SFE is measured within 10 scale radii. The final bound fraction increases with $γ$ values for a given global SFE. We conclude that Dehnen clusters better resist the consequences of the violent relaxation followed the instantaneous gas expulsion than the Plummer clusters. Thus the shallower the outer density slope of the low-SFE clusters, the better for their survivability after gas expulsion. Among Dehnen clusters we find that the steeper the inner slope (cusp) the higher the bound mass fraction is retained after violent relaxation for a given global SFE.

astro-ph.GA↗