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)

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.

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).

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

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

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

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.

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.

Carina Muñoz et al. 2006

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.

~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

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

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

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!!

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

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

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

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

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

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

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.

Questions?

Result for Leo I

Result for Leo I