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Alyson Brooks Fairchild Postdoctoral Fellow in Theoretical Astrophysics Caltech

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

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Alyson Brooks Fairchild Postdoctoral Fellow in Theoretical Astrophysics Caltech

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

  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 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 a) The Creation of a Bulgeless Disk Galaxy with a Dark Matter “Core” b) How to Create Large Disks despite Major Mergers

  6. N=1,000,000 100,000 30,000 x1019 atoms cm-2 20 kpc 20 kpc 20 kpc What is the role of resolution in forming realistic disk galaxies? Rd=30% smaller • Isolated (non-cosmological) galaxy simulation • MW mass halo after 5 Gyr Low resolution: disks heat and lose angular momentum to halo Kaufmann et al. (2007)

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

  8. “Zoom in” technique:high resolution halo surrounded by low resolution region Computationally Efficient Cosmic Infall and Torques correctly included 6 Mpc 100 Mpc 1 million particles 3 million particle simulation Katz & White (1993)

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

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

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

  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 a) The Creation of a Bulgeless Disk Galaxy with a Dark Matter “Core” b) How to Create Large Disks despite Major Mergers

  13. What is the role of feedback in forming realistic disk galaxies? No feedback feedback Zavala et al. (2008) Scannapieco et al. (2008)

  14. What is the role of feedback in forming realistic disk galaxies? 1) “Over-cooling” leads to loss of angular momentum similar to low resolution Maller & Dekel (2002)

  15. What is the role of feedback in forming realistic disk galaxies? • 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. Sub-grid physics & Blastwave Feedback Model • 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 LMC HI distribution (Stavely-Smith 2003) Stinson et al. (2006), Governato et al. (2007)

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

  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 a) The Creation of a Bulgeless Disk Galaxy with a Dark Matter “Core” b) How to Create Large Disks despite Major Mergers

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

  20. The Formation of a Bulgeless Dwarf Galaxy Mvir = 2x1010 M M* = 1.2x108 M 15 kpc on a side Green = gas Blue/Red = age/metallicity weighted stars

  21. Resolving Star Forming Complexes The effect of altering the SF density threshold 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. “Observed” Surface Brightness Profile 18 20 22 24 Mag/arsec2 Diffuse Star Formation 0 1 2 3 4 5 6 7 Radius (kpc) 22 24 26 28 “Resolved” Star Formation Mag/arsec2 0 1 2 3 4 Governato et al., 2009, Nature, accepted arXiv:0911.2237 Radius (kpc)

  24. Outflows Remove Low Angular Momentum Gas Gas removal from the galaxy center Hot gas perpendicular to disk plane: 100km/sec Cold Gas in shells = 30 km/sec Accreted material J At high z outflows remove low angular momentum gas at a rate 2-6 times SFR(t) Outflows Time 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. Clumpy Gas transfers orbital energy to DM via dynamical friction DM expands as gas is rapidly removed Diffuse SF: weak outflows Dark Matter with a Central Core 5 million particles DM Density 2 million particles SF in high density regions: strong outflows Log Radius (kpc) 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 a) The Creation of a Bulgeless Disk Galaxy with a Dark Matter “Core” b) How to Create Large Disks despite Major Mergers

  28. A case study: The Formation of a Large Galaxy Disk in a Low z Major Merger

  29. NO GAS 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 CDM  mergers Mergers or Smooth Gas Accretion?

  30. NO GAS ACCRETION NO GAS Mergers destroy or thicken disks Or do they? 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 (fgas > 50%) e.g., Toth & Ostriker 1992, Kazantzidis et al. 2007, Bullock et al. 2008, Purcell et al. 2008 Therefore, disk galaxies must grow rather quiescently CDM  mergers Mergers or Smooth Gas Accretion?

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

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

  33. What is the effect of cold flow gas accretion on the growth of galaxy disks?

  34. 3.4x1010 M 1.3x1011 M 1.1x1012 M 3.3x1012 M Gas Accretion Rates at the Virial Radius Brooks et al. (2009)

  35. Gas Accretion Rates Disk Star Formation Rates 3.4x1010 M 1.3x1011 M 1.1x1012 M 3.3x1012 M Brooks et al. (2009)

  36. z = 1 Historic Problem : Disk Growth After z=1, dramatic change in scale lengths since z=1 3.4x1010 M 1.3x1011 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) 1.1x1012 M 3.3x1012 M

  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)

  39. What is the effect of feedback on the growth of galaxy disks?

  40. 5 10 Age of Universe (Gyr) The Role of Feedback Develop a gas reservoir, yet fgas never > 25% Bulge SFR (M/yr) Brooks et al. (2009), Governato et al. (2009)

  41. SFR increases by ~2-3x in mergers 5 10 Age of Universe (Gyr) The Role of Feedback Bulge SFR (M/yr) 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 Young stellar disk, formed after last major merger (z < 0.8); 30% of z=0 disk mass (but dominates the light) ~30 % due to cold gas accreted prior to lmm; ~35% due to cold gas accreted after lmm; ~30% due to hot gas accretion Old stellar disk, formed prior to last major merger (z > 0.8); 70% of z=0 stellar disk mass Brightness not to scale!

  43. Disk Regrowth B/Di = 1.1 B/DM* = 1.2 M*disk = 2.07x1010 M B/Di = 0.49 B/DM* = 0.87 M*disk = 3.24x1010 M Sunrise: Jonsson (2006) www.ucolick.org/~patrik/sunrise/

  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

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