. Genomics for Universal Healthcare in Thailand1,2

Séguin, Béatrice; Hardy, Billie-Jo; Сингер, Петер; Daar, Abdallah S.

doi:10.1093/med/9780195374759.003.0060

Cited by 3 publications

(6 citation statements)

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“…However, simulations with different spherical potentials by showed that the shell radii depend only on the potential of the primary and probably on where the secondary disrupts. In addition, departures from a radial collision can change the dynamical friction effect and modify our analysis (Seguin & Dupraz 1996). Additionally, in modeling the gravity of the host galaxy, we used simplified assumptions.…”

Section: Discussionmentioning

confidence: 99%

“…The oscillations continue until the dwarf loses all its mass or completely merges with the host and the centers of density coincide. Multi-generation shell structures, caused by mul-tiple crossings, commonly form in self-consistent simulations (Seguin & Dupraz 1996;Bartošková et al 2011;Cooper et al 2011). It has been shown in test-particle simulations (Dupraz & Combes 1986;Ebrova et al 2012;Bílek et al 2013) that for a minor merger model, the observed wide range of shell radii requires the shell system to be formed in several generations.…”

Section: Dwarf Motionmentioning

confidence: 99%

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Type I Shell Galaxies as a Test of Gravity Models

Vakili

Kroupa

Rahvar

2017

ApJ

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Shell galaxies are understood to form through the collision of a dwarf galaxy with an elliptical galaxy. Shell structures and kinematics have been noted to be independent tools to measure the gravitational potential of the shell galaxies. We compare theoretically the formation of shells in Type I shell galaxies in different gravity theories in this work because this is so far missing in the literature. We include Newtonian plus dark halo gravity, and two non-Newtonian gravity models, MOG and MOND, in identical initial systems. We investigate the effect of dynamical friction, which by slowing down the dwarf galaxy in the dark halo models limits the range of shell radii to low values. Under the same initial conditions, shells appear on a shorter timescale and over a smaller range of distances in the presence of dark matter than in the corresponding non-Newtonian gravity models. If galaxies are embedded in a dark matter halo, then the merging time may be too rapid to allow multi-generation shell formation as required by observed systems because of the large dynamical friction effect. Starting from the same initial state, in the dark halo model the observation of small bright shells should be accompanied by large faint ones, while for the case of MOG, the next shell generation patterns iterate with a specific time delay. The first shell generation pattern shows a degeneracy with the age of the shells and in different theories, but the relative distance of the shells and the shell expansion velocity can break this degeneracy.

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Section: Discussionmentioning

confidence: 99%

Section: Dwarf Motionmentioning

confidence: 99%

Type I Shell Galaxies as a Test of Gravity Models

Vakili

Kroupa

Rahvar

2017

ApJ

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“…Quinn (1984) was the first to suggest that shells could be remnants of a small galaxy accreted by a much more massive primary host. Many of the simulations and semi-analytical models that followed have focused on idealized minor mergers, with satellites initialized on purely or nearly radial infall trajectories (e.g., Dupraz & Combes 1986;Hernquist & Quinn 1987b, 1988, 1989Seguin & Dupraz 1996;Weil & Hernquist 1993;Sanderson & Bertschinger 2010;Bartošková et al 2011;Ebrová et al 2012;Ebrova 2013). Moreover, in most cases, these set-ups correspond to direct hits where the satellite is initialized with ∼zero impact parameter.…”

Section: Progenitors Of Shellsmentioning

confidence: 99%

“…To reach this conclusion, Dupraz & Combes (1987) required the cores of the accreted satellites to survive several pericenter approaches, in order to explain observations of inner shells (e.g., Wilkinson et al 1987). It is expected that new generations of shells are produced as more and more stars are stripped from the companion at each successive passage near the central galaxy (Seguin & Dupraz 1996;Bartošková et al 2011;Cooper et al 2011;Ebrova 2013). This is in agreement with shell galaxies in Illustris, with studies of the satellites' trajectories indicating that the disruption of the companion happens over several pericentric approaches (see Figure A1).…”

Section: Progenitors Of Shellsmentioning

confidence: 99%

“…Therefore, just like streams and other low surface brightness features, shells are the outcome of the process of hierarchical assembly, and they have also been seen in the context of ΛCDM cosmological simulations (see, e.g., Cooper et al 2010Cooper et al , 2011. However, most of the previous studies investigating the formation of shells have focused on idealized, isolated minor mergers, involving satellites on radial infall trajectories (e.g., Dupraz & Combes 1986;Hernquist & Quinn 1987b, 1988, 1989Seguin & Dupraz 1996;Sanderson & Bertschinger 2010;Bartošková et al 2011;Ebrová et al 2012). The present study aims to test the statistically dominant shell formation mechanism by using for the first time a systematic, large sample of 220 massive galaxies from the cosmological gravity+hydrodynamics Illustris simulation.…”

Section: Introductionmentioning

confidence: 99%

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Formation and incidence of shell galaxies in the Illustris simulation

Pop

Pillepich

Amorisco

et al. 2018

Monthly Notices of the Royal Astronomical Society

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Shells are low surface brightness tidal debris that appear as interleaved caustics with large opening angles, often situated on both sides of the galaxy center. In this paper, we study the incidence and formation processes of shell galaxies in the cosmological gravity+hydrodynamics Illustris simulation. We identify shells at redshift z=0 using stellar surface density maps, and we use stellar history catalogs to trace the birth, trajectory and progenitors of each individual star particle contributing to the tidal feature. Out of a sample of the 220 most massive galaxies in Illustris (M 200crit > 6 × 10 12 M ), 18%±3% of the galaxies exhibit shells. This fraction increases with increasing mass cut: higher mass galaxies are more likely to have stellar shells. Furthermore, the fraction of massive galaxies that exhibit shells decreases with increasing redshift. We find that shell galaxies observed at redshift z = 0 form preferentially through relatively major mergers ( 1:10 in stellar mass ratio). Progenitors are accreted on low angular momentum orbits, in a preferred time-window between ∼4 and 8 Gyrs ago. Our study indicates that, due to dynamical friction, more massive satellites are allowed to probe a wider range of impact parameters at accretion time, while small companions need almost purely radial infall trajectories in order to produce shells. We also find a number of special cases, as a consequence of the additional complexity introduced by the cosmological setting. These include galaxies with multiple shellforming progenitors, satellite-of-satellites also forming shells, or satellites that fail to produce shells due to multiple major mergers happening in quick succession.

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Chandrasekhar's dynamical friction and non-extensive statistics

Silva¹,

Lima²,

Souza³

et al. 2016

J. Cosmol. Astropart. Phys.

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Abstract. The motion of a point like object of mass M passing through the background potential of massive collisionless particles (m << M ) suffers a steady deceleration named dynamical friction. In his classical work, Chandrasekhar assumed a Maxwellian velocity distribution in the halo and neglected the self gravity of the wake induced by the gravitational focusing of the mass M . In this paper, by relaxing the validity of the Maxwellian distribution due to the presence of long range forces, we derive an analytical formula for the dynamical friction in the context of the q-nonextensive kinetic theory. In the extensive limiting case (q = 1), the classical Gaussian Chandrasekhar result is recovered. As an application, the dynamical friction timescale for Globular Clusters spiraling to the galactic center is explicitly obtained. Our results suggest that the problem concerning the large timescale as derived by numerical N -body simulations or semi-analytical models can be understood as a departure from the standard extensive Maxwellian regime as measured by the Tsallis nonextensive q-parameter.

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. Genomics for Universal Healthcare in Thailand1,2

Cited by 3 publications

References 0 publications

Type I Shell Galaxies as a Test of Gravity Models

Type I Shell Galaxies as a Test of Gravity Models

Formation and incidence of shell galaxies in the Illustris simulation

Chandrasekhar's dynamical friction and non-extensive statistics

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