1. Modeling the Extended Structure of Dwarf Spheroidals (Carina, Leo I)
Ricardo Muñoz (University of Virginia)
In collaboration with:
Steven Majewski (University of Virginia)
Kathryn Johnston (Columbia University)

2. Goal of this talk
Readdress the question (one more time) to what extent Galactic tides may be affecting dSph galaxies:
Carina in particular, most compelling case for tidal stripping besides Sgr.
More specifically:
Are one-component, mass-follows-light models really inappropriate?
Have they really been ruled out in a tidal interaction scenario?
Under what circumstances (if any) can they reproduce the salient properties of Carina?
Goals of the talk.

3. Motivation
MW-satellite interactions have been modeled (many times) to try and understand how they would affect the internal kinematics of dSphs.
It’s generally agreed that:
If satellite is destroyed or near destruction, then artificial “inflation” of M/L is observed (e.g., Kroupa 1997).
If satellite retains a significantly bound core, the central velocity dispersion does reflect the instantaneous mass content (e.g., Oh, Lin & Aarseth 1995, Piatek & Pryor 1995).

4. Motivation rlim Carina Sculptor Draco Ursa Minor Leo I Sag.
Muñoz et al., 2006
Carina
Sculptor
Westfall et al. 2006
Draco
Muñoz et al. 2005
Ursa Minor
Muñoz et al. 2005
Leo I
Sohn et al. 2007
Sag.
Majewski et al. in prep.
Ibata et al. (1997).
rlim

5. Motivation
Not what it is expected from one-component, mass-follows-light model in equilibrium!
Gilmore et al. 2007

6. Motivation Problem with flat velocity dispersion profiles?:
Tidal stripping can cause them
Piatek & Pryor 1995
Velocity Dispersion Profiles
Mayer et al. 2001

7. Motivation Problem with flat velocity dispersion profiles?:
Tidal stripping can cause them, but:
Apparently no clear signs of tidal stripping in dSphs? For example: regular shapes, no tidal tails, lack of rotation
then need second mechanism.
Solve Jeans’ equations and get underlying mass distribution using some assumption for anisotropy
extended dark matter halos.

8. The case of Carina
Over the last years there has been significant effort to measure RVs of stars at large radii.
To date Carina is system with most extended radial coverage (both photometric and spectroscopic) and observations indicate some degree of tidal stripping.

9. Carina
Muñoz et al. 2006

10. Our Simulations:
-Milky Way: Miyamoto-Nagai 1975 disk, Hernquist spheroid and logarithmic halo. Parameters from Law, Johnston & Majewski 2005
-Satellite: 105 particles. Single-component (mass-follows-light), Plummer distribution.

11. ~250 Simulations for Carina, ~100 for Leo I
Our Simulations:
Wide exploration of parameter space:
Mass: 1 x 106 to 3 x 108 Mo
Scale length: 90, 194, 280 and 480 pc
Orbit: Nearly Circular to 0.9 eccentricity
Satellite is required to have current RV of
Carina and be at same distance and position.
~250 Simulations for Carina,
~100 for Leo I

12. Results for Carina:
Muñoz, Majewski & Johnston, ApJ, submitted.

13. Results for Carina
-Best Models: Orbital parameters of best model match those found by Piatek et al. (2003) from proper motion measurements.

14. Results for Carina: - Rather eccentric orbit (apo:peri 100:15 kpc)
Best Model properties:
- Rather eccentric orbit
(apo:peri 100:15 kpc)
- Current mass: ~2 x 107 MSUN
- Mass Loss Rate ~ 10% orbit-1
M/L ~ 40 (M/L)SUN
In agreement with results
from Core-Fitting technique!!

15. Very distant dSph: ~250 kpc, but high radial velocity: VGSR ~200 km/s
Result for Leo I
Very distant dSph: ~250 kpc, but high radial velocity: VGSR ~200 km/s
Best Model properties:
- Very eccentric orbit:
(apo:peri 400:13 kpc)
- Current mass: ~ 4.0 x 107 MSUN
- Mass Loss Rate: ~ 2% Gyr-1
M/L ~ 5 (M/L)SUN
In agreement with results
from Core-Fitting technique!!
Sohn et al. 2007

16. Results for Leo I -Best Model Orbit: 2 perigalacticon model
favored but not required.
Only 10-15% of initial mass
in tidal tails.

17. Mass-follows-light?
Total density distribution
Mayer et al. 2001:
Multi-component Low Surface Brightness dwarf evolves roughly into MFL system through tidal stripping (broadly similar to Klimentowski et al. 2007)
Luminous density distribution

18. Mass-follows-light?
Johnston and Bullock simulations:
When DM halo is stripped to the point that stars are stripped, then system behaves like MFL.

19. Appearances can be deceiving
Other General Results
Appearances can be deceiving
25.5 mag/arcsec2
32 mag/arcsec2

20. Appearances can be deceiving
Other General Results
Appearances can be deceiving
32 mag/arcsec2

21. Conclusions/Future Work:
dSphs like Carina and Leo I are currently well described by simple, single-component, MFL models undergoing tidal stripping. This is not inconsistent with the satellites starting as multi-component systems.
Fraction of satellites currently being tidally disrupted can be used as another constrained in cosmological simulations.

22. Questions?

23. Result for Leo I

24. Result for Leo I