THE KINEMATICS OF THE LOCAL GROUP IN A COSMOLOGICAL CONTEXT

Journal Article · Wed Apr 10 04:00:00 EDT 2013 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/767/1/L5· OSTI ID:22130762

Forero-Romero, J. E. ^[1]; Hoffman, Y. ^[2]; Bustamante, S. ^[3]; Gottloeber, S. ^[4]

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1. Departamento de Fisica, Universidad de los Andes, Cra. 1 No. 18A-10, Edificio Ip, Bogota (Colombia)
2. Racah Institute of Physics, The Hebrew University of Jerusalem, 91904 Jerusalem (Israel)
3. Instituto de Fisica-FCEN, Universidad de Antioquia, Calle 67 No. 53-108, Medellin (Colombia)
4. Leibniz-Institut fuer Astrophysik, Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany)

Recent observations constrained the tangential velocity of M31 with respect to the Milky Way to be v{sub M31,tan} < 34.4 km s{sup -1}and the radial velocity to be in the range v{sub M31,rad} = -109 {+-} 4.4 km s{sup -1}. In this study we use a large volume high-resolution N-body cosmological simulation (Bolshoi) together with three constrained simulations to statistically study this kinematics in the context of the {Lambda} cold dark matter ({Lambda}CDM). The comparison of the ensembles of simulated pairs with the observed Local Group (LG) at the 1{sigma} level in the uncertainties has been done with respect to the radial and tangential velocities, the reduced orbital energy (e{sub tot}), angular momentum (l{sub orb}), and the dimensionless spin parameter, {lambda}. Our main results are (1) the preferred radial and tangential velocities for pairs in {Lambda}CDM are v{sub r} = -80 {+-} 20 km s{sup -1} and v{sub t} = 50 {+-} 10 km s{sup -1}, (2) pairs around that region are 3-13 times more common than pairs within the observational values, (3) 15%-24% of LG-like pairs in {Lambda}CDM have energy and angular momentum consistent with observations, while (4) 9%-13% of pairs in the same sample show similar values in the inferred dimensionless spin parameter. It follows that within current observational uncertainties the quasi-conserved quantities that characterize the orbit of the LG, i.e., e{sub tot}, l{sub orb}, and {lambda}, do not challenge the standard {Lambda}CDM model, but the model is in tension with regard to the actual values of the radial and tangential velocities. This might hint to a problem of the {Lambda}CDM model to reproduce the observed LG.

• OSTI ID: 22130762
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 767; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTROPHYSICS
COSMOLOGICAL MODELS
MILKY WAY
NONLUMINOUS MATTER
ORBITS
RADIAL VELOCITY
RESOLUTION
SIMULATION
SPIN