EDP Sciences
Free access
Issue
A&A
Volume 421, Number 2, July II 2004
Page(s) L29 - L32
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040183


A&A 421, L29-L32 (2004)
DOI: 10.1051/0004-6361:20040183

Letter

Probing the Canis Major stellar over-density as due to the Galactic warp

Y. Momany1, S. R. Zaggia2, P. Bonifacio2, G. Piotto1, F. De Angeli1, L. R. Bedin1 and G. Carraro1

1  Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
    e-mail: [momany;piotto;carraro;deangeli;bedin]@pd.astro.it
2  INAF - Osservatrio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy
    e-mail: [zaggia;bonifacio]@ts.astro.it

(Received 20 April 2004 / Accepted 25 May 2004 )

Abstract
Proper-motion, star counts and photometric catalog simulations are used to explain the detected stellar over-density in the region of Canis Major, claimed to be the core of a disrupted dwarf galaxy (CMa, Martin et al. 2004, MNRAS, 348, 12; Bellazzini et al. 2004, [arXiv:astro-ph/0311119]), as due to the Galactic warp and flare in the external disk. We compare the kinematics of CMa M-giant selected sample with surrounding Galactic disk stars in the UCAC2 catalog and find no peculiar proper motion signature: CMa stars mimic thick disk kinematics. Moreover, when taking into account the Galactic warp and flare of the disk, 2MASS star count profiles reproduce the CMa stellar over-density. This star count analysis is confirmed by direct comparison with synthetic color-magnitude diagrams simulated with the Besançon models (Robin et al. 2003, A&A, 409, 523) that include the warp and flare of the disk. The presented evidence casts doubt on the identification of the CMa over-density as the core of a disrupted Milky Way satellite. This however does not make clear the origin of over-densities responsible for the ring structure in the anticenter direction of the Galactic halo (Newberg et al. 2002, ApJ, 569, 245; Yanny et al. 2003, ApJ, 588, 824).


Key words: astrometry -- Galaxy: structure -- Galaxy: formation -- Galaxies: interactions

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