Tidal Streams in the Milky Way (and M31) Jorge Peñarrubia (University of Victoria, Canada) & David Martinez Delgado (IAC, Spain) 22th of June 2006 Valencia

1-Tidal streams Tidal streams result from the disruption of stellar systems They provide information on: 1. The Milky Way potential on large distance scales ( kpc) 2. The mass and orbit of the progenitor 3. The stellar evolution within the progenitor 4. The formation of spiral galaxies Tidal streams represent a powerful tool to test cosmological predictions

2- The Sgr stream. Status The Sgr stream was the first major evidence that the MW may have formed through hierarchical infall of smaller systems Current theoretical picture

SDSS data q h =0.8 q h =1.4 Y Z R The Sgr stream may be passing close (<5 kpc) to the solar neighbourhood. An unvaluble target for RAVE (Radial Velocity survey) Future experiments aiming to detect dark matter emission The Virgo over-density Martinez-Delgado, Peñarrubia et al. (in prep.)

3- The Monoceros Stream In contrast to the Sgr stream, the Mon stream appears to be located on low latitudes. First detected by Newberg et al. (2002) with SDSS data. By collecting all available observational data, Peñarrubia et al. (2005) constrained the progenitor orbit: e=0.10  0.05 ; i=25±5 deg. Theoretical models predict a stream age < 3 Gyr

4- M31 … twin sister of the Milky Way? M31 has a mass and structure similar to the Milky Way. Did M31 follow a similar formation process? M31 also suffered a recent merger of a massive, highly eccentric satellite galaxy moving on an eccentric orbit, visible today in form of the Giant Stream Sgr model

Recently, Ibata et al. (2005) detected a giant extended disc (R<80 kpc) which might be the remants of a low-latitude, low-eccentricity merger (similar to the Mon stream’s progenitor) Peñarrubia, McConnachie & Babul (2006) Mon stream model