Phys/Astro 689: Lecture 8. Angular Momentum & the Cusp/Core Problem

Transcription

1 Phys/Astro 689: Lecture 8 Angular Momentum & the Cusp/Core Problem

2 Summary to Date We 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

3 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).

4 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.

5 Angular Momentum in Halos ZAVALA ET AL. (2008) In TTT, so J ~ t

6 Angular Momentum in Halos In TTT, DM and gas should initially have same J distribution van den Bosch et al. (2002)

7 The Problem The angular momentum profile in real galaxies does not match predictions van den Bosch et al. (2001)

8 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)

9 Does reionization help? No van den Bosch et al. (2003)

10 Big bulges are rare, and sometimes there is no bulge A large bulge Introduce bulgeless disk galaxies A bulgeless disk

11 Big bulges are rare, and sometimes there is no bulge Sersic profiles describe galaxy light distribution DUTTON (2009)

12 The first bulgeless disk galaxy simulation Jonsson (2006), Jonsson et al. (2010)

13 The Importance of Driving Outflows Mvir ~ 1010 Msun dwarf galaxy Edge on disk orientation (arrows are velocity vectors) Brook et al., (2011)

14 Outflows Remove Low Angular Momentum Gas HI + All baryons ever in the galaxy Add P(j) slide Brook et al. (2011) j/j tot van den Bosch et al. (2001)

15 Outflows Remove Low Angular Momentum Gas Brook et al. (2011)

16 Outflows Reduce the Inner Rotation Curve Teyssier et al. (2012) No Feedback Feedback + Delayed Cooling see also: Governato et al., 2010, Nature, 463, 203, arxiv:

17 This requires high resolution! High threshold Low threshold See also: Saitoh et al. (2008), Ceverino & Klypin (2009) Robertson & Kravtsov (2008), Tasker & Bryan (2008)

18 Outflows Reduce the Inner Rotation Curve The effect of altering the SF density threshold V circ%% =% The effect of altering resolution Governato et al., 2009, Nature, 463, 203, arxiv:

19 Observed Surface Brightness Profile Mag/arsec ! 22! 24! Diffuse Star Formation Radius (kpc) Mag/arsec 2 24! 26! 28! Resolved Star Formation Radius (kpc)

20 The current state Simulators can now make bulgeless disks Realistic bulges up to a few 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).

21 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)

22 Best Test: Low Surface Brightness Galaxies tend to be bulgless have central surface brightnesses fainter than 23 mag/arcsec 2 lie low on the mass-metallicity relation dark matter dominated!

23 LSBs favor a constant density core MOORE 1994, NATURE

24 The Cusp/Core Problem Parameterize density profile as!(r) r -" Simulations predict " ~ 1 (central cusp) Observations show " ~ 0 (constant-density core)

25 But... your data sucks van den Bosch et al. (2000) Flores & Primack (1994) data: Carnignan & Freeman (1988), Carnignan & Beulieu (1989)

26 Example degeneracy α = 1.30 α = 0.26 α = 0.80 SOLID: BEST FIT MODEL, INCLUDING RESOLUTION EFFECTS GREEN: STARS BLUE: DM HALO DOTTED: HI THIN RED: TOTAL

27 Simon et al. (2005) Enter the Era of Better Data

28 OH ET AL. (2011) Enter the Era of Better Data THINGS: The HI Nearby Galaxies Survey resolution: 7, 5km/s

29 Theorists counter with Non- Circular Motions Valenzuela et al. (2006): observed HI rotation curve true rotation curve cold gas in a simulated dwarf galaxy

30 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)

31 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).

32 Potential Core Creation Mechanisms: Angular Momentum Arguments DEL POPOLO (2009)

33 Potential Core Creation Mechanisms: Bars 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)

34 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?

35 Theorists accidentally made a DM core typical Qield dwarf Bulgeless! Exponential stellar disk, Rd ~ 1 kpc Gas rich Vc < 60 km/sec bursty SFH SFR ~ 0.01 Msun/yr GOVERNATO ET AL. (2010)

36 How Are Cores Created? Bursty SF! Core creation due to rapid potential well fluctuations PONTZEN & GOVERNATO 2012

37 Outflows Flatten the DM Density Profile Core Creation!

38 ρ ~ r -α Galaxies in the THINGS survey have average α~-0.3

39 Cores found by many Teyssier 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: 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

40 Core Creation varies with Mass! because SF varies with mass Galaxies in the THINGS survey have average α~-0.3 Governato et al., 2012, MNRAS, 422, 1231 Lower mass galaxies do not undergo repeated bursts of SF; retain cusps

41 Core Creation varies with Mass! because there s not enough energy at low masses Penarrubia et al. (2012) Core creation requires enough E in stellar feedback (young stars, SNe) to unbind the cuspy DM

42 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

43 And what happens at higher masses? NEWMAN ET AL. (2013)

44 The current state General 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)