1. The Virgo Stellar Stream
Third Chilean Advanced School in Astrophysics
The Virgo Stellar Stream
The Virgo Stellar Stream: a win- win
thesis project...
Sonia Duffau E.
Maria Teresa Ruiz, Robert Zinn, Kathy Vivas, Giovanni Carraro, René Méndez
Sonia Duffau E.

2. Third Chilean Advanced School in Astrophysics
Outline
Tidal tails and Dark matter
VSS, VOD or Sgr. ?
Martinez-Delgado views v/s our data
Discussion and work ahead
10 enero 2007
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Outline
Sonia Duffau E.

3. Tidal streams, Cosmology and DM Halo
Third Chilean Advanced School in Astrophysics
Tidal streams, Cosmology and DM Halo
-Ultimate goal: to infer the formation process of the Milky Way
from the properties of the present fossil records.
-Find (or not) the predicted merger remnants from the hierarchical
build-up view of our Galaxy.
10 enero 2007
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Intro to subject
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4. Tidal tails and Dark matter
Third Chilean Advanced School in Astrophysics
Tidal tails and Dark matter
Study of tidal tails by means of:
Observations
Comparison with models
Example model of Sgr. : Law’s models
Sonia Duffau E.

5. Third Chilean Advanced School in Astrophysics
Tidal Debris of the Sagittarius Dwarf Spheroidal
This webpage is intended to serve as a companion resource to the discoveries recently presented by Majewski and collaborators in the following suite of 6 papers:
A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy
Paper I: Morphology of the Sgr Core and Tidal Arms (Majewski et al. 2003, ApJ, 599, 1082)
Paper II: Swope Telescope Spectroscopy of M Giant Stars in the Dynamically Cold Sagittarius Tidal Stream (Majewski et al. 2004a, ApJ, 128, 245)
Paper III: Constraints on the Flattening of the Galactic Halo (Johnston, Law, & Majewski 2004, ApJ Submitted, astro-ph/)
Paper IV: Modeling the Sagittarius Tidal Tails (Law, Johnston, & Majewski 2004, ApJ Submitted, astro-ph/)
Paper V: Radial Velocities of Leading Debris (Majewski et al. 2004b, in preparation)
Paper VI: Globular Cluster Associations (Majewski et al. 2004c, in preparation)
Sep. 24 press release on Paper I
The following resources may be of interest to those who are interested in studying the Sgr dwarf and its tidal streams. These are all the work of David R. Law.:
A description of the Sgr longitudinal coordinate system (Paper I).
C++ code to convert from Galactic coordinates into the Sgr coordinate system.
Full spatial data for the best fit Sgr models (Paper IV).
3D "flyaround" movie of the best fit Sgr models.
Click!
Copyright Notice:
Please note that all papers are the copyright of the respective journals in which they are published. Any publications wishing to use data available on this website should acknowledge this website as the source for that data.
Sonia Duffau E.

6. Third Chilean Advanced School in Astrophysics
Best-fitting Sgr disruption models
Simulations are realized using 10^5 particles in a self-consistent field code (see Paper IV). These files have 16 columns of data as given below. All distances are in kpc, all velocities in km/s, and all angular measurements are in degrees.
Lambda_sun: orbital longitude.
Beta_sun: orbital latitude.
l: Galactic longitude.
b: Galactic latitude.
X_GC: Standard left-handed Galactocentric Cartesian coordinate.
Y_GC: Standard left-handed Galactocentric Cartesian coordinate.
Z_GC: Standard left-handed Galactocentric Cartesian coordinate.
X_sun: Right-handed heliocentric Cartesian coordinate in the Lambda_sun system.
Y_sun: Right-handed heliocentric Cartesian coordinate in the Lambda_sun system.
Z_sun: Right-handed heliocentric Cartesian coordinate in the Lambda_sun system.
U: Galactic U velocity (left-handed frame).
V: Galactic V velocity (left-handed frame).
W: Galactic W velocity (left-handed frame).
d: Heliocentric distance.
vgsr: Radial velocity relative to the Galactic Standard of Rest (NB: GSR, not LSR).
Pcol: "Color", or unbound era of simulated particle.
Data files are provided below for the three models discussed in Paper IV (oblate,spherical,
and prolate Galactic halo models).
Oblate (q=0.9) model.
Spherical (q=1.0) model.
Prolate (q=1.25) model. Up
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7. Third Chilean Advanced School in Astrophysics
A bit of history
VSS
Sgr
First discovered
in Carbon stars
by Ibata, 1994.
All sky view by
means of M
giants from the
2MASS survey
(Majewski et al.
2003)
Vivas´s thesis
finds it on QUEST
data,
VSS
QUEST detects
over-density in RR Lyrae towards Virgo (12.4 hr clump)
SDSS detects MS turnoff
(S )
QUEST/Yale/
Calan does first spectroscopic follow up (VSS)
SDSS constructs first density maps (VOD) towards Virgot
Sgr.
Radial distribution plot for all QUEST data
10 enero 2007
Third Chilean Advanced School in Astrophysics
Intro to VSS, VOD and Sgr.
Sonia Duffau E.

8. Spectrosocpy of QUEST RR Lyrae variables: The new Virgo Stellar Stream
Third Chilean Advanced School in Astrophysics
Spectrosocpy of QUEST RR Lyrae variables: The new Virgo Stellar Stream
Fig. 2
RRLy and BHBs in the area
Location of 12.4 hr clump
Fig. 1
Duffau et al. 2006, ApJ, 636, L97-L100
10 enero 2007
Third Chilean Advanced School in Astrophysics
Sonia Duffau E.

9. Third Chilean Advanced School in Astrophysics
Results
Metallicity
<[Fe/H]> = dex
σ = 0.4 dex
σ(int) = 0.08 dex
Radial velocity
<Vgsr> = 99.8 km/s
σ = 17.3 km/s
<Vgsr> = 83.2 km/s
σ = 24.5 km/s
σ(meas) = 18.8 km/s
Overdensity of RRLy
Non-gaussian velocity distribution
Suspect Stellar Stream from a disrupted Dwarf galaxy
Located in the direction of Virgo
New Virgo Stellar Stream (VSS)
More spectroscopic observations for january 2007!
10 enero 2007
Third Chilean Advanced School in Astrophysics
Sonia Duffau E.

10. SDSS density maps and the VOD
Third Chilean Advanced School in Astrophysics
Contrast with
Galaxy model
Virgo overdensity
Juric et al.,
astro-ph /
Astro-ph paper by SDSS identifying overdense extended feature in direction of Virgo
10 enero 2007
Third Chilean Advanced School in Astrophysics
Sonia Duffau E.

11. Sgr. falling down the plane?
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Sgr. falling down the plane?
10 enero 2007
Third Chilean Advanced School in Astrophysics
Intro to astro-ph
Sonia Duffau E.

12. Sgr. Debris towards Virgo the physical link
Third Chilean Advanced School in Astrophysics
Sgr. Debris towards Virgo the physical link
Oblate model by Law
Even older passages
Three orbits ago
Two orbits ago
Unbound durina the last orbit
Martinez-delgado et al. 2006, astro-ph/
Intro to M-D views
10 enero 2007
Third Chilean Advanced School in Astrophysics
Sonia Duffau E.

13. Martinez-Delgado oblate model
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Martinez-Delgado oblate model
Particles unbound only 2.5 Gyrs ago
VOD stars consistent with model
Sun
10 enero 2007
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M.D. astro-ph
Sonia Duffau E.

14. Third Chilean Advanced School in Astrophysics
Oblate
Prolate
3-D view Model
Low density=blue
High density = red
VSS in dark box
VOD in white box
Yellow point is the sun
10 enero 2007
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M.D astro-ph
Sonia Duffau E.

15. Artist’s view of the problem
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Artist’s view of the problem
Oblate
Prolate
10 enero 2007
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M. D. conference PPT
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16. Third Chilean Advanced School in Astrophysics
Is it all Sagittarius ?
Oblate
Prolate
VSS
Duffau et al. (2006)
Leading arm
Leading arm
Trailing arm
10 enero 2007
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M-D comparison
Sonia Duffau E.

17. Third Chilean Advanced School in Astrophysics
So what is it then ?
In the case of VOD it seems clear that it is unlikely unrelated to Sgr. but SDSS has no velocity info yet…
In the case of the VSS if it is related to Sgr. ,it is related to stars from an old passage of the satellite still undetected, if not, it is a completely new event!
Any of these cases makes this a great result, and valuable data for near field cosmology
10 enero 2007
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Discussion
Sonia Duffau E.

18. VLT results and Virgo paper
Third Chilean Advanced School in Astrophysics
VLT results and Virgo paper
For our latest results on Sagittarius and the Virgo paper please look for poster 14 on the panels !!!
VLT spectroscopy of RR Lyrae stars in the
Sagittarius northern tidal stream
S. Duffau (Universidad de Chile), M. T. Ruiz (Universidad de Chile), R. Zinn (Yale University) & A. K. Vivas (CIDA institute)
Abstract: We present VLT spectroscopy of 13 RR Lyrae variables from the QUEST survey that lie in the leading arm of the tidal stream from Sagittarius dSph galaxy. We observed these stars to measure their radial velocities and metal abundances and to complete a sample of stars from the overdensity detected by QUEST in this area of the sky. The full sample contains 42 stars, 29 observed with VLT and 13 observed with GEMINI, we report here the results from the VLT observations so far. We conclude that the new stars and stars reported before by Vivas, Zinn and Gallart, 2005, are consistent with belonging to Sgr. We discuss the importance of the final third of the sample, the GEMINI targets, which will provide important constrains on models of the Sgr streams that assume different dark matter halo shapes.
Sgr.
Introduction: A detailed study of the Sgr. tidal tails may help us understand Galaxy formation in many ways. Sgr is the prototypical case of the process of tidal disruption and galaxy merger, providing insight on a process that might be responsible for the formation of the luminous halos of galaxies like our own. The stellar populations along the tails might have evolved under the presence of the strong tidal forces, this can be revealed by comparing different stellar populations at different location on the streams. Finally the streams have been proposed as possibly powerful tools to study the shape of the Milky Way´s potential, which at large galactocentric distances (like the ones involved in this study), may be dominated by the shape of the dark matter halo (DM). Theoretical models of Sgr tidal disruption under assumptions of different DM halo shapes differ on small scales. The precisions that are necessary to distinguish between these small differences observationally are achieved with RR Lyrae stars because they are excellent standard candles providing their location in space very precisely, much more than with other tracers. The ultimate goal of this research is to test models of the streams that assume different shapes for the gravitational potential of the MW, using both the high positional accuracy of RR Lyrae stars and their radial velocities. For the moment we have studied two thirds of the intended sample using VLT. GEMINI data on the last third will follow.
Fig. 1: radial plot of RR Lyrae from QUEST
10 enero 2007
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Sonia Duffau E.

19. Third Chilean Advanced School in Astrophysics
10 enero 2007
Third Chilean Advanced School in Astrophysics

20. Spatial distribution of VSS
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LARIM 2005 Pucón
12-16 December
Spatial distribution of VSS
Region of sky with excess of stars with respect to control field
Mag interval ~19.5 < g < 20.5
Found in at least 106 deg2 of the searched area
Closer to the Sun
Searched
Zone 1
Zone 2
10 enero 2007
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Sonia Duffau E.

21. Extended Search of VSS using SDSS
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Extended Search of VSS using SDSS
Feature extends at least 106 deg2 on the sky
2σ Poisson excess threshold
Pal 5
Virgo
Central
region
Less
prominent
detection
10 enero 2007
Third Chilean Advanced School in Astrophysics
Sonia Duffau E.

22. Velocity distribution
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Velocity distribution
Central Region
Distribution is non-Gaussian
Main peak has <Vgsr> = 99.8 and σ = 17.3 km/s
Average error=18.8 km/s
Evidence for a New Stellar Stream, the VSS
Possibility of more than one group will be explored
Main
Peak
Outside
central
region
10 enero 2007
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Sonia Duffau E.

23. Sample Star distribution
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BHBs from Sirko et al. (2004) AJ 127, 899.
Sample Star distribution
Central region
Circles= QUEST RRLy
Triangles=BHBs
Small symbols have no spectral information
Dashed box=¨Central region¨
Solid=possible members of a new Stellar Stream
RRLy expected, 8 found!
10 enero 2007
Third Chilean Advanced School in Astrophysics
Sonia Duffau E.

24. QUEST RRLy survey and the 12.4 hr clump
Third Chilean Advanced School in Astrophysics
QUEST RRLy survey and the 12.4 hr clump
Plot showing the ¨12.4 hr clump¨ selected for spectroscopic follow-up
Also identified by Newberg et al
A. K. Vivas, PhD Thesis, Yale University, 2001
Newberg et al. 2002
ApJ 569, 245
Sgr
Pal 5
10 enero 2007
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RA vs. Heliocentric distance for QUEST RRLy zone 1 targets
Sonia Duffau E.