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Dynamic and Spatial Properties of Satellites
in Isolated Galactic Systems
Abel B. Diaz
Presentation Outline
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Rotation Curves: Probing the mass distribution
The Problem
Rotation Curves of Isolated Galaxy Systems
Stellar properties of Satellites
The Holmberg effect
2D Rotation Curve
Rotation Curves:
Probing the mass distribution
• Within Galaxy
– Well known
• External to Galaxy
– Not well known
Fritz Zwicky (1933)
Babcock (1939)&Vera Rubin (1970)
The Problem
• How does the mass distribution of galaxies
change with distance beyond the disk of
the galaxy?
What would this tell us?
• Learning more about the mass distribution
of isolated galaxies may provide insight
into galaxy
– formation
– evolution
– LSS
So how can this be done?
• Rotation Curves of Isolated Galaxy Systems
– Dominate source of gravitation
• The center-of-mass of the system is located at center
of “primary” galaxy
– Satellites relatively small compared to primary
• Maintains center-of-mass located at the center of
primary
Limits on Isolated Galaxies
1. Small number of detectable satellites
2. Line-of-sight velocity
3. Projected distance
Isolated Galaxy Ensembles
Interlopers
• Observed redshift = cosmological redshift + Doppler redshift
• The peculiar velocities of the satellites can be on the order of
400km/s
• Uncertainty of distance along the line-of-sight
Velocity Dispersions
McKay (2002), Prada et al (2003),
and Brainerd (2004)
The Data Sample
• New York University Value-Added Galaxy
Catalog (NYU-VAGC)
– Lowz (Sub Sample of ~50,000 galaxies)
Ensembles
Robust Analysis
Velocity Dispersion Curve
Prada et al (2003), and Brainerd (2004)
Galaxies Types
Early vs. Late
• Early type galaxies have
larger halos than late type
galaxies
• Conroy et al. (2007)
What These Results Tell Us
• Rotation curve (consistent with NFW)
– Supports hierarchical scenario
• Halo sizes
– Larger primordial dark matter halos for early
type galaxies than for late type galaxies
Stellar Properties
• How does the satellite stellar properties change
as a function of distance from the primary?
– Star formation from self gravity or tidal effects from
primary
Stellar properties of Satellites
What Does This Mean
• Primaries cause "tidal" effects on their
satellites
– Kosh and Grebal (2006)
• More pronounced in satellites with
primaries that have a larger mass (halo)
• Different distribution in Systems at larger z
(longer ago)
The Holmberg Effect
Holmberg (1969)
Modeling
• Check for Isotropy
– polar fraction ~0.70
– Mean f = 45 degrees
• Interloper check
– P/T >> 0.5
Results for Primary tilt < 30o
No Holmberg found in my data
f  45.5
o
Kolmogorov-Smirnov (KS) test
Results for Varying tilts angle
No Holmberg found in my data
Binned Results for Primary tilt < 30o
Brainerd (2005)
Sales & Lambas (2004), Koch & Grebel (2006)
Zaritsky et al. (1997)
Binned Results for Primary tilt > 60o
What does this tell us?
• Dark Matter halo
– Spherical
• Puts constraints on models
– Infall through fillaments
2D Velocity Dispersions
• Velocity Distribution
– Isotropic about primary
tilt ~ 45
• DM halo
– Spherical
2
R    f2 sin 2 i   z2 cos 2 i
 maj
2
R cos i    R2 sin 2 i   z2 cos 2 i
 min
tilt ~ 45
Conclusion
• The Dynamic Properties
– Dark Matter Halos
• Different sizes for different type of galaxies
• Consistent with NFW (hierarchical scenario)
• The Spatial Properties
– Satellites are isotropically distributed, and
have isotropic velocity distribution
• Spherical Dark Matter Halo
– Star formation depends on distance from their
primary
• Primaries effect their satellites