Title: Modeling the Extended Structure of the Carina Dwarf Spheroidal
1Modeling the Extended Structure of the Carina
Dwarf Spheroidal
Ricardo Muñoz (University of Virginia)
- In collaboration with
- Steven Majewski (University of Virginia)
- Kathryn Johnston (Wesleyan University)
2Goal 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?
- Under what circumstances (if any) can they
reproduce the salient properties of Carina?
3Motivation
- MW-satellite interactions have been modeled (many
times) to try and understand how they would
affect the internal kinematics of dSphs.
- Weve learned that
- If satellite is destroyed or near destruction,
then artificial inflation of M/L is observed
(Kroupa 1997).
- If satellite retains a significantly bound core,
the central velocity dispersion does reflect the
instantaneous mass content (Oh, Lin Aarseth
1995, Piatek Pryor 1995).
- Velocity gradient (apparent rotation) is main
indicator of tidal stripping (e.g., Piatek
Pryor 1995, Read et al. 2006)
4Motivation
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, ApJ, in press
Sag.
Majewski et al. in prep. Ibata et al. (1997).
rlim
5Motivation
- Not what it is expected from one-component,
mass-follows-light model not being tidally
disrupted!
Gilmore et al. 2007
6Motivation
- 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.
7The 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.
8Carina
Muñoz et al. 2006
9Our 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.
10Our 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.
200 Simulations for Carina, 100 for Leo I
11Results for Carina
Muñoz, Majewski Johnston, in prep.
12Results for Carina
-Best Models Orbital parameters similar to the
ones found by Piatek et al. (2003) from proper
motion measurements.
13Results for Carina
- Best Model properties
- - Rather eccentric orbit
- (apoperi 10015 kpc)
- - Initial mass 3.8 x 107 MSUN
- - Mass Loss Rate 10 orbit-1
M/L 40 (M/L)SUN In agreement with result
s
from Core-Fitting technique!!
14Very little stripping can cause flat/rising
velocity dispersion profile
Result for Leo I
- Best Model properties
- - Very eccentric orbit
- (apoperi 40013 kpc)
- - Current mass 4.0 x 107 MSUN
- - Mass Loss Rate 2 Gyr-1
M/L 5 (M/L)SUN In agreement with resu
lts
from Core-Fitting technique!!
Sohn et al. 2007, ApJ, in press
15- Johnston and Bullock simulations
When DM halo is stripped to the point that
stars are stripped, then system behaves like MFL.
16Lack of rotation can be deceiving
Other General Results
No velocity gradient?
17Lack of rotation can be deceiving
Other General Results
18Lack of rotation can be deceiving
Other General Results
19 and appearances can be deceiving
Other General Results
20 and appearances can be deceiving
Other General Results
21- A dark matter-dominated, MFL system undergoing
tidal stripping provides a very good match to all
the observed properties of Carina (and Leo I).
Premature to rule out MFL
- Very little tidal stripping can greatly affect
velocity dispersion profile. Remove outliers
(Klimentowski et al. 2006)
- Apparent rotation not convenient as a tidal
disruption indicator (if limited to King radius)
- Sensitivity of current photometric and
spectroscopic surveys may not be enough to find
signatures of tidal stripping. MORE
DATA
22