phys/astro 689: lecture 8abrooks/689/phys689_lecture8.pdf · phys/astro 689: lecture 8 angular...
Post on 21-Jun-2020
8 Views
Preview:
TRANSCRIPT
Phys/Astro 689: Lecture 8Angular Momentum & the Cusp/Core Problem
Summary to DateWe first learned how to construct the Power Spectrum with CDM+baryons.
Found CDM agrees with the observed Power Spectrum on large scales; now trying to test small scales
Must follow galaxies in the non-linear regime to test small scales. Have learned about the tools to do this: DM-only and DM+baryonic simulations
Angular Momentum in Halos
Linear Tidal Torque Theory: matter acquires angular momentum due to forces from external matter (up to large distances).
Linear Tidal Torque Theory, originally worked out in White (1984).
Angular Momentum in Halos
Principal axes of tidal and inertia tensors not generally aligned for non-spherical volume, so net angular momentum results.
J acquisition stops at turn-around.
Angular Momentum in Halos
In TTT, so J ~ t
ZAVALA ET AL. (2008)
Angular Momentum in HalosIn TTT, DM and gas should initially have same J distribution
van
den
Bosc
h et
al. (
2002
)
The Problem
The angular momentum profile in real galaxies does not match predictions
van den Bosch et al. (2001)
The Problem The angular momentum profile in real galaxies does not match predictions (even when uncertainties are considered)
e.g., stellar M/L ratios, asymmetric drift
van den Bosch et al. (2001)
Does reionization help?
No
van den Bosch et al. (2003)
Big bulges are rare, and sometimes there is no bulge
Introduce bulgeless disk galaxies
A large bulge
A “bulgeless” disk
Big bulges are rare, and sometimes there is no bulge
DUTTON (2009)
Sersic profiles describe galaxy light distribution
Big bulges are rare, and sometimes there is no bulge
The first bulgeless disk galaxy simulation
Jonsson (2006), Jonsson et al. (2010)
The Importance of Driving Outflows
Mvir ~ 1010 Msun “dwarf galaxy”
Edge on disk orientation
(arrows are velocity vectors)
Brook et al., (2011)
Outflows Remove Low Angular Momentum Gas
Add P(j) slide
HI +
All baryons ever in the galaxy
j/jtotvan den Bosch et al. (2001)Brook et al. (2011)
Outflows Remove Low Angular Momentum Gas
Brook et al. (2011)
Outflows Reduce the Inner Rotation Curve
see also: Governato et al., 2010, Nature, 463, 203, arXiv:0911.2237
No Feedback Feedback + Delayed Cooling
Teyssier et al. (2012)
High threshold Low threshold
See also: Saitoh et al. (2008), Ceverino & Klypin (2009)Robertson & Kravtsov (2008), Tasker & Bryan (2008)
This requires high resolution!
Outflows Reduce the Inner Rotation Curve
The effect of altering the SF density threshold
The effect of altering resolution
V circ%%=%
Governato et al., 2009, Nature, 463, 203, arXiv:0911.2237
!
Diffuse Star Formation
“Resolved” Star Formation
Radius (kpc) 0 1 2 3 4 5 6 7
18
Mag
/ars
ec2
Radius (kpc)
22
28 Mag
/ars
ec2
0 1 2 3 4
24!
26!
20!
22!
24!
“Observed” Surface Brightness Profile
The current state
Simulators can now make bulgeless disks
Realistic bulges up to a few 1011 in halo mass (Christensen et al. 2013)
Going to higher mass galaxies requires higher resolution. Realistic bulges in MW mass galaxies are yet to be achieved (but very close).
The Cusp/Core problem
All that low angular momentum material at the center of DM halos also leads to higher central densities than observed
It’s not just the normalization of the density, it’s also the distribution (slope of the density profile)
Best Test: Low Surface Brightness Galaxies
tend to be bulgless
have central surface brightnesses fainter than 23 mag/arcsec2
lie low on the mass-metallicity relation
dark matter dominated!
LSBs favor a constant density core
MOO
RE 19
94, N
ATUR
E
The Cusp/Core Problem
Parameterize density profile as !(r) ∝ r -"Simulations predict " ~ 1 (central cusp)
Observations show " ~ 0 (constant-density core)
But... your data sucks
Flores & Primack (1994)data: Carnignan & Freeman (1988),
Carnignan & Beulieu (1989)
van den Bosch et al. (2000)
Example degeneracyα = 1.30 α = 0.26 α = 0.80
SOLID: BEST FIT MODEL, INCLUDING RESOLUTION EFFECTSGREEN: STARS
BLUE: DM HALODOTTED: HI
THIN RED: TOTAL
Simon et al. (2005)
Enter the Era of Better Data
THINGS: The HI Nearby Galaxies Survey
resolution: 7”, 5km/s
Enter the Era of Better Data
OH ET AL. (2011)
Theorists counter with Non-‐Circular Motions
cold gas in a simulated dwarf galaxy
Valenzuela et al. (2006):
“true” rotation curve
“observed” HI rotation curve
Potential Core Creation Mechanisms: Dynamical Friction
(1) The effect of gravity causes light bodies in the parent halo to accelerate and gain momentum and kinetic energy. By conservation of energy and momentum, we may conclude that the heavier body will be slowed by an amount to compensate.
(2) Equivalently, the light bodies are attracted by gravity toward the larger body moving through the cloud, and therefore the density at that location increases (a gravitational wake). In the meantime, the object under consideration has moved forward. Therefore, the gravitational attraction of the wake pulls it backward and slows it down.
See also El-Zant (2001,2004), Tonini et al. (2006), Jardel & Sellwood (2009)
Potential Core Creation Mechanisms: Dynamical Friction
Perhaps the gas clumps are accelerated at the center of the galaxy rather than accreted (e.g., Mashchenko et al. 2006, 2008).
Potential Core Creation Mechanisms: Angular Momentum Arguments
DEL POPOLO (2009)
109 1014
J is transferred by resonance in bar pattern speed and orbits of DM in inner halo (see Weinberg & Katz, 2002)
But see Sellwood (2008)
HOLLEY-BOCKELMANN ET AL. (2005)
Potential Core Creation Mechanisms: Bars
What about outflows?
Galactic winds appear to be required to match the observed angular momentum distribution in galaxies.
Can they simultaneously solve the cusp/core problem?
Theorists accidentally made a DM core
•Bulgeless!•Exponential stellar disk, Rd ~ 1 kpc•Gas rich•Vc < 60 km/sec•bursty SFH•SFR ~ 0.01 Msun/yr
“typical” Qield dwarf
GOVERNATO ET AL. (2010)
Core creation due to rapid potential well fluctuations
How Are Cores Created?Bursty SF!
PONTZEN & GOVERNATO 2012
Outflows Flatten the DM Density Profile
Core Creation!
ρ ~ r-α
Galaxies in the THINGS survey have
average α~-0.3
Cores found by manyTeyssier et al. (2013), RAMSES (AMR) code
• Navarro et al.,1996, MNRAS, 283, L73• Read & Gilmore 2005, MNRAS, 356, 107• Mashchenko et al.,2006, Nature, 442, 539• Mashchenko et al., 2008, Science, 319, 174• PaseLo et al., 2010, A&A, 514, A47
• Ogiya & Mori 2012, arXiv:1206.5412• de Souza et al., 2011, MNRAS, 415, 2969• Cloet-‐Osselaer et al., 2012, MNRAS, 423, 735• Maccio et al., 2012, ApJ, 744, L9• Teyssier et al., 2013, MNRAS, 429, 3068
Galaxies in the THINGS survey
have average α~-0.3
Lower mass galaxies do not undergo repeated bursts of SF; retain
cusps
Core Creation varies with Mass! because SF varies with mass
Governato et al., 2012, MNRAS, 422, 1231
Core creation requires enough E in stellar feedback (young stars, SNe) to unbind the cuspy DM
Penarrubia et al. (2012)
Core Creation varies with Mass! because there’s not enough energy at low masses
But Do Cores Exist? Stellar vs Gas Kinematics
Adams et al. (2011)VIRUS-P
NGC 2976
poster child for a core using gas,
stars are consistent with a cusp
And what happens at higher masses?
NEWMAN ET AL. (2013)
The current stateGeneral question about whether stars have enough energy to create cores
Do cores exist at high masses?
Ongoing observational tests; LSB dwarfs seem to have cores, higher masses are under debate
DI CINTIO ET AL. (2013)
top related