1. Alyson Brooks Fairchild Postdoctoral Fellow in Theoretical Astrophysics Caltech In collaboration with the University of Washington’s N-body Shop ™ makers of quality galaxies The Formation of Realistic Galaxy Disks

2. Outline I. Simulating Realistic Disk Galaxies is the Necessary Starting Point for Comparison to Observations a) The Effect of Resolution b) The Effect of Feedback II. What we Learn II. What we Learn a) The Creation of a Bulgeless Disk Galaxy with a Dark Matter “Core” b) How to Create Large Disks despite Major Mergers

3. Fully Cosmological, Parallel, N-body Tree Code, + smoothed particle hydrodynamics (SPH) Stadel (2001) Wadsley et al. (2004)

4. Galaxy Formation: Now with AMR!

5. Outline I. Simulating Realistic Disk Galaxies is the Necessary Starting Point for Comparison to Observations a) The Effect of Resolution b) The Effect of Feedback II. What we Learn II. What we Learn a) The Creation of a Bulgeless Disk Galaxy with a Dark Matter “Core” b) How to Create Large Disks despite Major Mergers

6. Low resolution: disks heat and lose angular momentum to halo Rd=30% smaller Kaufmann et al. (2007) 20 kpc x10 19 atoms cm -2 N=1,000,000 100,000 30,000 Isolated (non-cosmological) galaxy simulation MW mass halo after 5 Gyr

7. The CDM Angular Momentum Problem Navarro & Steinmetz (2000) Disks are too small at a given rotation speed Disks rotate too fast at a given luminosity Mass (dark and luminous) is too concentrated Log V rot MIMI catastrophe!

8. “Zoom in” technique: high resolution halo surrounded by low resolution region 3 million particle simulation 1 million particles Computationally Efficient Cosmic Infall and Torques correctly included 6 Mpc100 Mpc Katz & White (1993)

9. HI W20/2 velocity widths = V max Geha et al. (2006) Brooks et al., in prep Governato et al. (2008, 2009) baryonic Tully-Fisher relation (magnitudes from Sunrise)

10. Size - Luminosity Relation Brooks et al., in prep. Data from Graham & Worley, 2008 Simulated Galaxies Observed Sample

11. Naab et al. (2007) Mayer et al. (2008) As resolution increases, V peak decreases Same mass galaxies, but with and without feedback With feedback = Disk galaxies! Without feedback = Elliptical galaxies!

12. Outline I. Simulating Realistic Disk Galaxies is the Necessary Starting Point for Comparison to Observations a) The Effect of Resolution b) The Effect of Feedback II. What we Learn II. What we Learn a) The Creation of a Bulgeless Disk Galaxy with a Dark Matter “Core” b) How to Create Large Disks despite Major Mergers

13. No feedback Zavala et al. (2008) Scannapieco et al. (2008)

14. 1) “Over-cooling” leads to loss of angular momentum similar to low resolution Maller & Dekel (2002)

15. 1) “Over-cooling” leads to loss of angular momentum similar to low resolution 2) “Over-cooling” leads to ONLY elliptical galaxies! No feedback  Thermal  Disable Cooling  Blastwave  ?

16. Star Formation: reproduces the Kennicutt-Schmidt Law; each star particle a SSP with Kroupa IMF Energy from SNII deposited into the ISM as thermal energy based on McKee & Ostriker (1977) Radiative cooling disabled to describe adiabatic expansion phase of SNe (Sedov- Taylor phase); ~20Myr (blastwave model) Only Free Parameters: SN & Star Formation efficiencies Sub-grid physics & Blastwave Feedback Model Stinson et al. (2006), Governato et al. (2007) LMC HI distribution (Stavely-Smith 2003)

17. Brooks et al. (2007) Erb et al. (2006) Tremonti et al. (2004) Maiolino et al. (2008) Stellar Mass (M  ) 12+log(O/H) Stellar Mass (M  ) 12+log(O/H) The Regulation of Star Formation due to Feedback

18. Outline I. Simulating Realistic Disk Galaxies is the Necessary Starting Point for Comparison to Observations a) The Effect of Resolution b) The Effect of Feedback II. What we Learn II. What we Learn a) The Creation of a Bulgeless Disk Galaxy with a Dark Matter “Core” b) How to Create Large Disks despite Major Mergers

19. Moving Forward: “Resolving” Star Formation Regions Density X low SF threshold Density X high resolution + high SF threshold Feedback becomes more efficient. (more outflows per unit mass of stars formed)

20. The Formation of a Bulgeless Dwarf Galaxy M vir = 2x10 10 M  M * = 1.2x10 8 M  15 kpc on a side Green = gas Blue/Red = age/metallicity weighted stars

21. The effect of altering the SF density threshold Resolving Star Forming Complexes The effect of altering resolution Governato et al., 2009, Nature, accepted arXiv: 0911.2237

22. “Observed” Rotation Curve Governato et al., 2009, Nature, accepted arXiv: 0911.2237

23. Diffuse Star Formation “Observed” Surface Brightness Profile “Resolved” Star Formation Radius (kpc) 0123 4 5 6 7 18 20 22 24 Mag/arsec 2 0 1 23 4 Radius (kpc) 22 24 26 28 Mag/arsec 2 Governato et al., 2009, Nature, accepted arXiv: 0911.2237

24. At high z outflows remove low angular momentum gas at a rate 2-6 times SFR(t) Time J Accreted material Outflows Gas removal from the galaxy center Hot gas perpendicular to disk plane: 100km/sec Cold Gas in shells = 30 km/sec Outflows Remove Low Angular Momentum Gas See also: van den Bosch (2002), Maller & Dekel (2002), Bullock et al. (2001)

25. Angular Momentum of Stellar Disk vs DM halo van den Bosch et al. (2001) The Angular Momentum Distribution of baryons must be altered to match observed galaxies

26. Dark Matter with a Central Core Diffuse SF: weak outflows 5 million particles 2 million particles SF in high density regions: strong outflows DM Density Log Radius (kpc) Clumpy Gas transfers orbital energy to DM via dynamical friction DM expands as gas is rapidly removed e.g., Mashchenko et al. (2007, 2008); El-Zant et al. (2004); Navarro et al. (1996); Mo & Mao (2004); Tonini et al. (2006)

27. Outline I. Simulating Realistic Disk Galaxies is the Necessary Starting Point for Comparison to Observations a) The Effect of Resolution b) The Effect of Feedback II. What we Learn II. What we Learn a) The Creation of a Bulgeless Disk Galaxy with a Dark Matter “Core” b) How to Create Large Disks despite Major Mergers

29. Mergers or Smooth Gas Accretion? Mergers destroy or thicken disks e.g., Toth & Ostriker 1992, Kazantzidis et al. 2007, Bullock et al. 2008, Purcell et al. 2008 Therefore, disk galaxies must grow rather quiescently NO GAS CDM  mergers

30. Mergers or Smooth Gas Accretion? CDM  mergers Mergers destroy or thicken disks e.g., Toth & Ostriker 1992, Kazantzidis et al. 2007, Bullock et al. 2008, Purcell et al. 2008 Therefore, disk galaxies must grow rather quiescently Baugh et al. 1996, Steinmetz & Navarro 2002, Robertson et al. 2006, Hopkins et al. 2008, Robertson & Bullock 2008 Not if the disks are gas rich (f gas > 50%) Or do they? NO GAS NO GAS ACCRETION

31. e.g., Peebles (1969), Rees & Ostriker (1977), Silk (1977), Binney (1977), White & Rees (1978), Fall & Efstathiou (1980), Somerville & Primack (1999) How Do Galaxies Get Their Gas? Dark Matter Halo + Hot Gas Cold Disk Infalling Gas

32. Not all gas is shock heated! Fraction of shocked gas is a strong function of galaxy mass Cold flow gas accretion due to both: 1.Mass threshold for stable shock 2.Even after shock develops, there can be cold gas accretion at high z in dense filaments Keres et al. (2005), Dekel & Birnboim (2006), Ocvirk et al. (2008), Agertz et al. (2009), Dekel et al. (2009) Case 1 Standard Case 2 This is already in the SAMs. This is not.

34. Gas Accretion Rates at the Virial Radius 3.4x10 10 M  1.3x10 11 M  1.1x10 12 M  3.3x10 12 M  Brooks et al. (2009)

35. Gas Accretion Rates Disk Star Formation Rates 3.4x10 10 M  1.3x10 11 M  1.1x10 12 M  3.3x10 12 M  Brooks et al. (2009)

36. 1.3x10 11 M  z = 1 3.4x10 10 M  1.1x10 12 M  3.3x10 12 M  Massive Disks at z=1: Vogt et al. (1996); Roche et al. (1998); Lilly et al. (1998); Simard et al. (1999); Labbe et al. (2003); Ravindranath et al. (2004); Ferguson et al. (2004); Trujillo & Aguerri (2004); Barden et al. (2005); Sargent et al. (2007); Melbourne et al. (2007); Kanwar et al. (2008); Forster-Shreiber et al. (2006); Shapiro et al. (2008); Genzel et al. (2008); Stark et al (2008); Wright et al. (2008); Law et al. (2009) Historic Problem : Disk Growth After z=1, dramatic change in scale lengths since z=1

37. The Formation of a Milky Way-Mass Galaxy to z=0 30 kpc on a side Green = gas Blue/Red = age/metallicity weighted stars

38. The Role of Cold Flows Disk growth prior to z=1 due to cold flows Brooks et al. (2009), Governato et al. (2009) Keres et al. (2008), Ocvirk et al. (2008), Agertz et al. (2009), Dekel et al. (2009), Bournaud & Elmegreen (2009)

40. The Role of Feedback Bulge SFR (M  /yr) Develop a gas reservoir, yet f gas never > 25% Age of Universe (Gyr) 510 Brooks et al. (2009), Governato et al. (2009)

41. The Role of Feedback Bulge SFR (M  /yr) SFR increases by ~2-3x in mergers Age of Universe (Gyr) 510 Heiderman et al. (2009), Jogee et al. (2008), Stewart et al. (2008), di Matteo et al. (2008), Hopkins et al. (2008), Cox et al. (2008), Daddi et al. (2007), Bell et al. (2005), Bergvall et al. (2003), Georgakakis et al. (2000)

42. Disk Regrowth ~30 % due to cold gas accreted prior to lmm; ~35% due to cold gas accreted after lmm; ~30% due to hot gas accretion Young stellar disk, formed after last major merger (z < 0.8); 30% of z=0 disk mass (but dominates the light) Old stellar disk, formed prior to last major merger (z > 0.8); 70% of z=0 stellar disk mass Brightness not to scale!

43. Sunrise : Jonsson (2006) www.ucolick.org/~patrik/sunrise/ Disk Regrowth B/D i = 1.1 B/D M* = 1.2 M* disk = 2.07x10 10 M  B/D i = 0.49 B/D M* = 0.87 M* disk = 3.24x10 10 M 

44. Conclusions Simulations are improving! (due to resolution and feedback) Bulgeless galaxies with shallow DM cores are compatible with a CDM cosmology Strong gas outflows can selectively remove low angular momentum gas (but force resolution < 100pc is required) Although mergers are expected to be common in CDM, this is not at odds with the existence of disks Filamentary gas accretion leads to the building of disks at higher z than predicted by standard models Feedback regulates SFR in galaxies, building a gas reservoir and limiting gas consumption in mergers