New insights into the Sagittarius stream EWASS, Turku July 8th, 2013 Martin C. Smith Shanghai Astronomical Observatory http://hubble.shao.ac.cn/~msmith/ Sagittarius dwarf spheroidal(ish) • Since its discovery in 1994, the Sagittarius dwarf spheroidal has been hugely important for understanding cosmology in our back yard Ibata et al (1994) Sagittarius dwarf spheroidal(ish) • Since its discovery in 1994, the Sagittarius dwarf spheroidal has been hugely important for understanding cosmology in our back yard • Its tidal tails have been traced around our entire galaxy Ibata et al (1994) 160 A. Helmi Southern Arc Sgr Core 45 Northern 0 Fluff -45 δ 45 0 Northern -45 Arm 180 90 0 270 180 90 0 270 180 LMC SMC Majewski et al (2003) α Fig. 6 2MASS revealing the streams from Sgr. Smoothed maps of the sky for point sources selected accord- ing to 11 Ks 12 and 1.00 < J Ks < 1.05 (top), and 12 Ks 13 and 1.05 < J Ks < 1.15 (bottom). Two≤ cycles≤ around the sky are− shown to demonstrate the≤ continuity≤ of features. (From− Majewski et al. 2003. Courtesy of Steve Majewski. Reproduced with permission of the AAS) database on the basis of their colors) were able to map the streams 360o around the sky as shown in Fig. 6. The vast extent of the Sgr dwarf streams has been used to con- strain the shape of the Galactic gravitational potential, albeit with conflicting results (Helmi 2004b; Johnston et al. 2005; Fellhauer et al. 2006). In the years to follow, many of the structures discovered in the halo would be linked to the Sgr debris (Newberg et al. 2002; Vivas et al. 2001; Martínez-Delgado et al. 2004). An exception to this is the Monoceros ring (Yanny et al. 2003; Ibata et al. 2003), a low-latitude stream towards the anticenter of the Galaxy, that spans about 100o in longitude at a nearly constant distance. It is somewhat of a semantic distinction to state that this structure is part of the stellar halo, or of the Galactic thin or thick disks. As yet, the nature of the feature and of the Canis Major over- density in a similar location at low Galactic latitude (Martin et al. 2004), are highly debated. Possible interpretations are that it is debris from an accreted satellite (e.g. Helmi et al. 2003; Martin et al. 2004; Peñarrubia et al. 2005; Martínez-Delgado et al. 2005), an overdensity associated to the Galactic warp (Momany et al. 2004, 2006), or even a projection effect caused by looking along the nearby Norma-Cygnus spiral arm (Moitinho et al. 2006). Recently, Grillmair (2006a) has mapped the structure of the Monoceros overdensity using SDSS, and showed that it consists, at least in part, of a set of very narrow low-latitude substructures (see Fig. 7), which can easily be explained by the models of Peñarrubia et al. (2005). It is worthwhile mentioning here that such a satellite may well perturb the Galactic disk, and induce departures from axial symmetry or overdensities such as e.g. Canis Major. Furthermore, the Sgr dwarf leading tail also appears to be crossing the Galactic plane at roughly the same location and distance as the ring (Newberg et al. 2007), and may well be responsible for some of the substructures observed. 123 Sagittarius dwarf spheroidal(ish) • Since its discovery in 1994, the Sagittarius dwarf spheroidal has been hugely important for understanding cosmology in our back yard • Its tidal tails have been traced around our entire galaxy Ibata et al (1994) 160 A. Helmi Southern Arc Sgr Core 45 Northern 0 Fluff -45 δ 45 0 Northern -45 Arm 180 90 0 270 180 90 0 270 180 LMC SMC Majewski et al (2003) α Fig. 6 2MASS revealing the streams from Sgr. Smoothed maps of the sky for point sources selected accord- ing to 11 Ks 12 and 1.00 < J Ks < 1.05 (top), and 12 Ks 13 and 1.05 < J Ks < 1.15 (bottom). Two≤ cycles≤ around the sky are− shown to demonstrate the≤ continuity≤ of features. (From− Majewski et al. 2003. Courtesy of Steve Majewski. Reproduced with permission of the AAS) database on the basis of their colors) were able to map the streams 360o around the sky as shown in Fig. 6. The vast extent of the Sgr dwarf streams has been used to con- strain the shape of the Galactic gravitational potential, albeit with conflicting results (Helmi 2004b; Johnston et al. 2005; Fellhauer et al. 2006). In the years to follow, many of the structures discovered in the halo would be linked to the Sgr debris (Newberg et al. 2002; Vivas et al. 2001; Martínez-Delgado et al. 2004). An exception to this is the Monoceros ring (Yanny et al. 2003; Ibata et al. 2003), a low-latitude stream towards the anticenter of the Galaxy, that spans about 100o in longitude at a nearly constant distance. It is somewhat of a semantic distinction to state that this structure is part of the stellar halo, or of the Galactic thin or thick disks. As yet, the nature of the feature and of the Canis Major over- density in a similar location at low Galactic latitude (Martin et al. 2004), are highly debated. Possible interpretations are that it is debris from an accreted satellite (e.g. Helmi et al. 2003; Martin et al. 2004; Peñarrubia et al. 2005; Martínez-Delgado et al. 2005), an overdensity associated to the Galactic warp (Momany et al. 2004, 2006), or even a projection effect caused by looking along the nearby Norma-Cygnus spiral arm (Moitinho et al. 2006). Recently, Grillmair (2006a) has mapped the structure of the Monoceros overdensity using SDSS, and showed that it consists, at least in part, of a set of very narrow low-latitude substructures (see Fig. 7), which can easily be explained by the models of Peñarrubia et al. (2005). It is worthwhile mentioning here that such a satellite may well perturb the Galactic disk, and induce departures from axial symmetry or overdensities such as e.g. Canis Major. Furthermore, the Sgr dwarf leading tail also appears to be crossing the Galactic plane at roughly the same location and distance as the ring (Newberg et al. 2007), and may well be responsible for some of the substructures observed. 123 Sagittarius dwarf spheroidal(ish) • Since its discovery in 1994, the Sagittarius dwarf spheroidal has been hugely important for understanding cosmology in our back yard • Its tidal tails have been traced around our entire galaxy • This is a wonderful probe of the Milky Way’s potential! Ibata et al (1994) 160 A. Helmi Southern Arc Sgr Core 45 Northern 0 Fluff -45 δ 45 0 Northern -45 Arm Law & Majewski (2010) 180 90 0 270 180 90 0 270 180 LMC SMC Majewski et al (2003) α Fig. 6 2MASS revealing the streams from Sgr. Smoothed maps of the sky for point sources selected accord- ing to 11 Ks 12 and 1.00 < J Ks < 1.05 (top), and 12 Ks 13 and 1.05 < J Ks < 1.15 (bottom). Two≤ cycles≤ around the sky are− shown to demonstrate the≤ continuity≤ of features. (From− Majewski et al. 2003. Courtesy of Steve Majewski. Reproduced with permission of the AAS) database on the basis of their colors) were able to map the streams 360o around the sky as shown in Fig. 6. The vast extent of the Sgr dwarf streams has been used to con- strain the shape of the Galactic gravitational potential, albeit with conflicting results (Helmi 2004b; Johnston et al. 2005; Fellhauer et al. 2006). In the years to follow, many of the structures discovered in the halo would be linked to the Sgr debris (Newberg et al. 2002; Vivas et al. 2001; Martínez-Delgado et al. 2004). An exception to this is the Monoceros ring (Yanny et al. 2003; Ibata et al. 2003), a low-latitude stream towards the anticenter of the Galaxy, that spans about 100o in longitude at a nearly constant distance. It is somewhat of a semantic distinction to state that this structure is part of the stellar halo, or of the Galactic thin or thick disks. As yet, the nature of the feature and of the Canis Major over- density in a similar location at low Galactic latitude (Martin et al. 2004), are highly debated. Possible interpretations are that it is debris from an accreted satellite (e.g. Helmi et al. 2003; Martin et al. 2004; Peñarrubia et al. 2005; Martínez-Delgado et al. 2005), an overdensity associated to the Galactic warp (Momany et al. 2004, 2006), or even a projection effect caused by looking along the nearby Norma-Cygnus spiral arm (Moitinho et al. 2006). Recently, Grillmair (2006a) has mapped the structure of the Monoceros overdensity using SDSS, and showed that it consists, at least in part, of a set of very narrow low-latitude substructures (see Fig. 7), which can easily be explained by the models of Peñarrubia et al. (2005). It is worthwhile mentioning here that such a satellite may well perturb the Galactic disk, and induce departures from axial symmetry or overdensities such as e.g. Canis Major. Furthermore, the Sgr dwarf leading tail also appears to be crossing the Galactic plane at roughly the same location and distance as the ring (Newberg et al. 2007), and may well be responsible for some of the substructures observed. 123 Along comes SDSS... • The most spectacular recent images have come from the Sloan Digital Sky Survey (SDSS), which traced the density of main-sequence turn-off stars in the halo Sagittarius Stream Belokurov et al.