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RevMexAA (Serie de Conferencias), 50, 17–18 (2018)

BIFURCATION IN TIDAL STREAMS OF SAGITTARIUS DWARF GALAXY:

NUMERICAL SIMULATIONS

Y. Camargo Camargo1 and R. Casas-Miranda2

RESUMEN

Se realizan simulaciones de N-cuerpos entre la galaxia enana Sagitario y la Vıa Lactea. La galaxia Sagitariose modela con dos componetes: halo de materia oscura y disco estelar. La Vıa Lactea se modela con trescomponentes: halo de materia oscura, disco estelar y bulbo. El objetivo de este trabajo es reproducir lasbifurcaciones en las corrientes de marea y las propiededes fısicas de la galaxia enana Sagitario. Para ello sesimula la interaccion del progenitor de esta galaxia con la Vıa Lactea. Aunque se reprodujeron las bifurcaciones,la posicion y propiedades fısicas del remanente de Sagitario no se puedieron reproducir simultaneamente.

ABSTRACT

We performed N-body simulations between Sagittarius dwarf galaxy and the Milky Way. The Sagittarius galaxyis modeled with two components: dark matter halo and stellar disc. The Milky Way is modeled with threecomponents: dark matter halo, stellar disc and bulge. The goal of this work is to reproduce the bifurcations inthe tidal tails and the physical properties of the Sagittarius dwarf galaxy. For it, we simulated the interactionof the progenitor of this galaxy with the Milky Way. Although bifurcations could be reproduced, the positionand physical properties of Sagittarius remnant could not be obtained simultaneously.

Key Words: galaxies: individual (Sagittarius)

1. INTRODUCTION

Sagittarius dwarf galaxy (Sgr) was discovered byIbata et al. (1995). Located near to the Galacticplane, it has been disrupted under gravitational tidalforces that have produced tidal streams, showing bi-furcations in the north tidal stream (Fellhauer et al.2006). It is accepted that Sgr is a spheroidal galaxy,however Penarrubia et al. (2010) consider its pro-genitor as a disc galaxy in order to reproduce thebifurcations located in the north tidal stream.In this work the progenitor of Sgr is modeled as astellar disc ( Lokas et al. 2013) within a Navarro,Frenk & White (NFW) dark matter halo, with avirial mass of 1×108M⊙ and 6.0×105 particles. TheMilky Way is simulated with stellar disc and bulgecomponents within a NFW dark matter halo with avirial mass of 95.21×1010M⊙ and 3.0×105 particles.The initial structures were constructed using GalIC

and the gravitational interaction was simulated withGADGET-2 for seven different angles (θ) betweenthe angular momenta of the orbit and of the stellardisc. The initial orbit of Sgr has a pericenter of 11.35kpc and an apocenter of 67.85 kpc. The initial radialand tangential velocity components were 171 km/sand −295 km/s, respectively. To achieve the theo-

1Universidad de Cundinamarca (ydcamargoc,racasasm@unal.edu.co).

2Universidad Nacional de Colombia.

retical calculation of the physical properties we usedthe method shown by Kroupa (1997) and Klessen etal. (1998).

2. RESULTS AND CONCLUSIONS

Figure 1 shows the tidal tails obtained in oursimulations. We found bifurcations similar to thereported by Belokurov et al. (2006). The simulatedbifurcations appear at almost the same position ofthe observed ones, but the remnants of the progen-itors do not reproduce the current position or thephysical properties observed. The closest simulatedbifurcation to the observed corresponds to θ = 130◦

at 5.0Gyr (see Figure 1). In contrast, Penarrubiaet al. (2010) found bifurcations at −20◦. This anglecorresponds in our simulations to θ = 160o. Table 1shows equatorial coordinates, distance and physicalproperties of the simulated remnant at θ = 130o. At5.0Gyr, we found that the mass-luminosity relationand σ0 have close values to those observed. Bifurca-tions in the north tidal tail are present, although thesimulated remnant is not found in the current posi-tion. At 6.2Gyr none bifurcation is detected and thedistance obtained in our simulations is the shortest,far away to the actual distance of the remnant.

Our results do not reproduce the position andphysical properties of Sgr simultaneously. The rem-nant mass of Sgr obtained in our simulations is oneorder of magnitude less than the estimated mass.

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18 CAMARGO CAMARGO & CASAS-MIRANDA

Fig. 1. Tidal tails obtained for different angles (θ) be-tween angular momenta of the orbit and of the stellardisc of Sgr.

TABLE 1

t (Gyr) Remnant position Physical properties

RA, dec

D(kpc)

5.0 224.07◦, 11.06◦ µ0 = 10.52 × 104 L⊙/kpc2

49.67 M/L = 70.48M⊙/L⊙

r1/2 = 3.08 kpc

σ0 = 8.23 km/s

6.2 282.82◦, −31.62◦ µ0 = 23.07 × 104 L⊙/kpc2

72.20 M/L = 193.15M⊙/L⊙

r1/2 = 0.62 kpc

σ0 = 9.08 km/s

REFERENCES

Belokurov, V. et al. 2006, ApJL, 642, L137Fellhauer, M. et al. 2006, ApJ, 651, 167Ibata, R. A., Gilmore, G. & Irwin, M. J. 1995, MNRAS,

277, 781Klessen, R. S. & Kroupa, P., 1998, ApJ, 498, 143Kroupa, P., 1997, NewA, 2, 139 Lokas, E. L., Gajda, G. & Kazantzidis, S., 2013, MNRAS,

433, 878Penarrubia, J. et al. 2010, MNRAS, 408, L26